Planning for the First University-Level Teaching Position

“She made herself a wall and told the kids to overcome it. Students who do not hit that wall are inferior and weak to failure. Nowadays the kids do not take instructors seriously anymore because the instructors do not try to build that wall. […] They will be quick to forget me but they will never forget Akutsu-Sensei.”
(Namiki-Sensei about Akutsu-Sensei, じょおうのきょうしつ - The Queens Classroom EP11)

Fortune smiled at me this term. A key professor took a parental leave from the ECE department and they were looking for a new instructor. This course is relatively tough to teach. I suspect because none of the faculty was willing to jump in and previous sessional instructors were also unavailable, they actually considered getting in some foreign aid. Having assisted this course before, I was taken into consideration for the interview process.

The interview process was straightforward. It was a series of interviews focusing on the overall capabilities of an instructor. First they want to see you in person and assess that you are not a moron. Self presentation-, listening-, and observation skills get you through that. The next thing they focus on is teaching quality assurance. In my case the interview was targeted at a specific course. You should know what your course will be about and have a detailed plan how you would organize the lecture. That includes not only the content of the lecture but also managerial considerations as to where to allocate TAs and how many TAs you get / are expected to work with. Finally someone will be invited to assess your background knowledge about specific topics of the course. This one could eventually be your biggest thread. You should now your stuff well. Some interviewers might drop you like a hot dish: “How can this guy dare to teach , if he doesn’t even know ”. Other interviewers might be leaner and still think you are smart enough to prepare well for your assignment.

If you pass this stage they will ask you to perform a demo lecture about a sub-section of the course. Mine went well and I was notified that I got accepted.

So now you got the job and your schedule for the next term will be shot. I expect to have little time for anything else than teaching this term. Trust me, you should not do this for money as you will end up putting far more hours in it than “expected”. If you are really short on cash consider Teaching Assistantships. If you screw up as instructor, you not only have an angry mob of undergrads after you, but you also risk your reputation in the department. Since academic communities are usually small, next time you apply for a faculty or instructor position that will be considered. An angry mob of undergraduates cannot really hurt you as long as you obey university policies and master some martial arts skills ;), but they can be really annoying. To have your peace of mind and be able to look back on an effective term those issues should, however, be avoided in the first place.

The first thing I worried about is, what resources and additional man power I would be getting. The next thing is to get in touch who-ever was instructing and or supporting the course before. The more old material you can get, the less stuff you have to prepare next term. In my case I was very lucky to connect with the previous instructor and lab instructor of the course. Most of the materials were obtained, slides, past exams, quizzes, and lab materials.

Engineering the Wall

•••••••••••••••▼The Wall▼•••••••••••••••

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┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴

┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬

┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴┬┴
(by some unknown very geeky ASCII artist)

Since the students have to metaphorically overcome your wall, you need to engineer it in the first place. The design depends on your resources (strength), the students’ experiences (height) and their cultural background (slope & approach) and your objectives.
Most of the findings in this section are a team effort and arose from discussion and high commitment from lab instructor, previous course instructors and TAs.

Thoughts on Wall Strength

I was in the lucky opportunity to get three excellent TAs and an experienced lab instructor. We have three lab sessions of three hours each every other week and weekly tutorials. With the lab you can get the students a deep dive on operating systems and acquiring practical development skills.

Thoughts on Wall Height

Traditionally, and in our case, we let them develop a simple embedded operating system from scratch. Given that they only have less than four months to complete the assignment is (expectedly) challenging. They are software engineers and come with some background in embedded assembly programming and C/C++ programming. Since they are software engineers, I also have no reservations exposing them to the full breath and depth of the operating systems subject.

Learning operating systems is not a mentally challenging task. The algorithms are relatively simple (scheduling, I/O interaction, concurrency) and easy to grasp. Most of the technical material is closely tied to the advances in the hardware community and ends up a lot to learn but is not really mentally challenging.

What is, however, quite challenging is putting the learned material to use in the lab. Therefore, I the course was traditionally worked to make the students make focus a large part of their effort on the project. Given the short lab timeframe, only the basics are covered in the lab.

Passing the lab will not let the students pass the final exam and just learning for the final exam will hardly make them pass the course. Lately the department enforced a minimum 50% weight on the final exam. If it was according to me, I would put much more weight on the project because these skills will certainly pay most of the dividends in their later career. In the past, instructors tried to combine these two areas, to have them evaluate code samples in quizzes/exams as well, which generally dragged the exam average down.

Thoughts on Wall Slope and Approach

As I mentioned before designing this part is the most challenging and depends on your objectives, the environment, and also the cultural background of your students.

Let’s start with the cultural background (or better university culture). Going to a traditional German university for my undergraduate and graduates study (well I fought at the European Council to have my Diploma recognized as MSc…long story), you come from a very different end of university culture than you see in North America. Nowadays the system is changing in Germany, but when I was doing my degree, the five year study were divided into two parts. A section of four basic semesters (i.e., there were only two terms per year) and a section of four advanced semesters. At my time the tuition was bogus, I paid like 70 EUR per term, and the study was largely government financed. As a result the student had no economic stake in pursuing the study and “the system” had great interest in letting unfit students fail early. Therefore the students would usually be sent through hell and high waters during the first four terms to extinct anyone who is not fit or does not commit to their studies. Operating systems would potentially fall into this primary study. After these four terms all course marks would be merged to establish a mid-examination mark. During my years it was not unusual to barely pass this with about 4 out of 5 where 1 is best (that would account for about~55% - 60%, on a grading scheme that is usually tougher than Canada). After that your program grades are reset and you pursue advanced studies that are usually comprised of several electives. During the advanced studies, exams are usually carried out orally, which have their own flavour but are, from my perspective, easier. To have an idea about the practical implications: my course of studies started with about 50 students. After the mid-examination we were about 12, who barely made it. As of today, I know about 6 who eventually graduated.

Many of them now work as research engineers in German automotive companies, pursued PhDs in Germany (actually all of those guys finished already… time to hurry up for me), or entered the middle or higher management of software companies like SAP.

The courses at my school usually consist of a lecture and occasional labs or tutorials. The courses spanned sometimes multiple terms before you had an exam and were back loaded. That means there was only one single final exam, which you would only be allowed to write after you finished all terms of the course. In my case, I had to wait one year to be able to write my math exam. Exams usually spanned multiple hours. This math exam for instance took five hours. Labs, tutorials and assignments were usually not marked; there were a few exceptions for practical courses like Embedded Systems, which usually occurred at the advanced level. All that counted was the final exam. Procrastination or trying to learn everything 2 weeks before the exam was in almost all cases fatal. Most lecturers were also following the traditional Latin meaning of “study” = “studere” in German: “nach etwas streben, sich um etwas bemühen”: To pursue something yourself; to make an effort yourself. Therefore, it was not usual to ask for problems in the exam that were not covered in detail in the lecture or tutorial. Lecture and tutorial were used to “illustrate” the material not necessarily to cover it in enough depth for the exam. The student was expected to read the course text, optional materials and develop the necessary skills to survive the exam. Only then they’d be valued as an Engineer, or otherwise extinct and thrown out of the program early. This property actually provided you with several freedoms that are hard to recognize first. Only a few instructors cared if you attend the lecture, tutorials, or labs, as long as you survive the exam. This could actually buy you plenty of free time, if you were well organized and skilled. Unfortunately, thanks to EU, austerity, and the introduction of student fees this original tough system has lost much of its traditional flavour over the past 5 years.

Then you come to North America, specifically Waterloo, and see a very different picture for undergraduate studies.

First, students here are actually heavily financially invested into their studies and the university runs as business. Therefore, letting them fail early seems to be big taboo here. The university does not seem to want to disgruntle students. Also university evaluations are carried out in a very different manner. If you had a few very bright people graduating from your program in Germany, you have many people graduating in Canada, with a few being very bright and starting off businesses. The few very bright individuals in both instances would dominate the news and be the selling point of your university. On the other hand, you still have a large mass of students who do not end up becoming CEOs or top-managers in Canada. Out of those, it is quite surprising how many people in Canada actually end up doing things that are totally unrelated to their initial study. It is in so far a surprise to me, because they not only spend a lot of time on it, but they also blew a lot of cash on it. Actually, most of this money comes from student loans, enslaving them for years to debt (another “business model” from the Canadian government).

Second, this is something that I would call North-American culture that has also been analyzed in the (controversial) research community.
These are some ideas that apply to the emergent mass and not necessarily individuals, however, may become emergent for an entire course.
Canadians seem to have the highest level of individualism (IDV), a low level of uncertainty avoidance (UAE), a low long term outlook (LTO) and a low power distance (PDI) compared to other regions.

As a result of LTO and UAE, studies tend to be more applied here and focus on the short-term “market” instead of fundamental research. Also hard-core corporate research labs are found elsewhere than in Canada. Thus, the study is much more applied here and incorporates more labs than in Germany. Therefore, the students also prefer a higher level of practical guidance, instead of leaving them to themselves and punishing them hard if they get it wrong. They also seem to work more ad-hoc here.

That may make them very prone to procrastination (i.e. ignoring the course/lab). They will eventually focus their attention where the pressure/fun comes from (other courses, evening activities …). Other areas may not have this problem. An instructor of mine in Germany, was teaching university-level math courses 20 years ago in Japan… he had trouble setting the standards high enough not to bore the students. Unfortunately, their system also lost much of its flavour over the past 20 years.

Talking to people about this issue there are a couple options to mitigate procrastination and promote continuous participation...

One option is a front-loaded course where most of the efforts are spent on a mid-term examination. You communicate to them that they should focus their attention on the mid-term and that will get burned there regardless (say scores in the high 60s) and an easier final (say scores expected in the high 80s). On the lab side, you also force them to focus their efforts in getting the project design right very early. This was done in the past by having them deliver a comprehensive software design document about half-way through the project. This approach seems to be the favoured option for many instructors here; well some are leaner on the mid-terms and still burn the students on the finals. However, for the actual lesson this does not provide optimal value. At the time the students write the software design document they have little idea what they are going to implement. It was usually communicated to them during the marking, how good or bad their design was and how the real thing should look like. Another issue is, because many instructors follow this model in other courses as well, the students will experience load surges during the term. Here is a good one, try to get hold of a UW undergrad during mid-term periodJ.

Another option is an even workload. Instead of making them write a mid-term, you let them do multiple short quizzes. That way you enforce continuous participation and give them a bit more time during mid-terms. Because the main lab-take-home is acquiring the development skills, we skip the SDD and focus on code deliverables right from the start that are spread out in multiple milestones. Finally, they will include the written design and the lessons learned in a final report. This poses more workload on the TAs and lab instructors in terms of marking, but almost entirely avoids procrastination on the student side and over the long run provides them with more insight into the course material. The risk of course failures is therefore reduced because they are implicitly prepared for the final exam and final course deliverable if they follow through. If they do not, they will eventually feel the pain of low marks right from the start and need to react and presumably catch up with the workload.

We (my lab instructor and me) favour and will use the even workload option, even when this means that I need to share some of the TA workload myself. I want to provide these guys with a high-quality course and ensure that they actually acquire skills in the lab and remember some of the course materials.

Summary

Teaching a course is not going to be a walk in the park. It takes plenty of effort and a good team of TAs and lab instructors. If you teach a course, consider the crowd, their background, their skills, and the established university culture. Be sure to work for the students and not against them. If you are from a different background, noticing such deviations is sometimes hard.

Also thanks to the previous instructors and the current lab instructor for in-depth discussions and input on the subject.

We will see how well that plays out in my case. As Clausewitz once said: “No plan survives the first battle!” … we will see if they tear my wall down J

References

• Willmanns & Hehl, “Praxis und Paradoxa des Innovationsmanagements” (In German).
  This is a good book for innovation and research management in Germany. After reading it, you notice the imprint that you’re educational and cultural background makes on you and how to deal with it.
• Hofstede, Cultural Dimensions.
  He quantitatively tries to analyze different cultures. The measures should not be stereotyped on individuals but give a rough idea what to expect, when you travel to a different background. His research is however quite controversial.
• じょおうのきょうしつ - The Queens Classroom.
  This is a TV series that I came across on a trip to Japan. The teacher has a great interest to prepare the kids for the tough and terribly competitive world in Japan, where bullying and forced subordination are a constant. The methods applied are very traditional and hardly represent what’s actually happening today. It is also exposing how traditional values are now ridiculed over there. Such draconian methods would obviously fail in adult education, specifically in Canada. It’s however a very curious TV series.
• Pink Floyd – The Wall.
  A song of the late 70s. It deals with the abuse by teachers and the situation of schools in Britain at the time. The wall in this case is however used as a metaphor for isolation and not effort (as in the citation before).
• Various management adult education books.

Fixing a Vintage Mercedes Rear Axle and Turning Your Schedule into a Living Nightmare

"Haste Hammer, Zange, Draht kommste bis nach Leningrad."

Hammer, pliers, wire  is all you need to get to Leningrad (St. Petersburg today).
(Former East German car owner mantra)


Deutsche Reparaturanleitung, hier...

Before I moved to Canada from Germany, I was a very opinionated person when it came to the reliability of North American and Japanese cars. I would not believe that anything else would come close to the maintainability and reliability of old diesel Mercs, particularly the Mercedes W123, W124, W126 and W201 series. I was a proud and convinced driver of a 1989 Mercedes 190D 2.0 in Germany for several years, despite outrageous ownership and emission fees over there. Upon acceptance into the PhD program in Waterloo, I finally decided to take my car with me from Germany to Canada. The big advantage of driving a Mercedes is worldwide coverage of dealerships and the availability of parts for several decades old cars. They run a recession proof business as long as people in recession proof positions favour Mercs, including Yakuzza bosses, Chinese communist party officials, religious leaders, political leaders, dictators, and taxi drivers. This property results outstanding worldwide coverage of dealerships that no other car manufacturer can offer even in political unstable regions and Banana Republics. Even in Japanese media, you see bad guys driving Mercs. People that reject such cars usually end up in trouble as well. By coincidence the guys driving the Mercs in the media also seem to have a better handle on economics, particularly compound interest in this case. Ok enough for the esoteric part ...

The other advantage of old Diesel Mercs is their easy maintainability. Everything is mechanically controlled and can mostly be fixed and diagnosed with standard tools (if you know how!). So in short for the past four years I ended up driving the first and only Mercedes 190D 2.0 in Ontario. Although this car has an excellent track record, after 21 years of serving well, even serious parts fail due to wear and tear.

What was Broken

Over the past few months, I noticed a rumbling noise in the back of the car that was very dominant at low velocities (< 30 kph) and higher velocities (> 100 kph). When driving faster, it actually caused vibrations on the steering wheel. The alleged cause of the trouble was a combination of broken rear-axle bushings and a constant velocity joint of the rear axle shaft. Because the rods of the wheel attachment have not been touched in the past 21 years, I decided to fix the whole thing, which means replacing all rear axle rods, the hand-brake cables, the rear axle bushings, the wheel bearings, the wheel carrier bushings, the spring carrier bushings, the axle shafts, and do some major rust prevention.

Turning the Schedule Upside-Down

In addition to the large number of required parts, it takes substantial amounts of time to put everything in pieces and back together. A garage in Germany, usually quotes you 3-4 days for the repair. I have seen people doing it in Germany and briefly assisted in doing such repairs on other models. Most people, including hobbyists in Germany, will tell you that this is not a super big job. My naive estimate was around 4 days, borrowing special tools and doing everything myself … boy was I wrong, it ended up taking two weeks, made me sacrifice beloved other hobbies, put my research work at risk, and, finally, made me visit several machine shops despite of the original plan of doing everything myself. The last one was a lesson itself because specialized shops are not as easy to find in Canada as in Germany.

What really hurt me was being without a garage and, hence, being dependent on the weather. Thus, I had to give the repairs the priority to avoid the winter weather and…

• Had to give up beginner Kendo classes for the term. I really loved this sport, but I missed out several classes in a row. It would be really disrespectful to the dojo to come unprepared or running behind the other club mates. I really hope that they offer a beginner class next term.
• Was thrown behind 1.5 weeks on a course project. If you always context-switch between repairs and research you really loose efficiency. Particularly, when you constantly worry about tomorrows weather.
• Missed out on driving to Algonquin Park and enjoy the Indian summer. Actually this was the original motivation for getting the job done ASAP in the first place.

Disclaimer

The remainder of the article gives you the example, why you shouldn’t attempt such repairs yourself outside of Germany if you don’t have your own garage, or, if you do, how to do it yourself and come up with more realistic duration estimates.

As a disclaimer, although I screwed up the time estimate in the first place, I still consider myself a quite advanced hobbyist. If you are new to car repairs, this job is quite big and nothing for beginners. There is at times also a substantial risk of serious injuries. If you perform this or any related repair, you assume the full risk of your actions. The author of this blog, me, does not assume any liability for the actions done by the readers and their peers.

What You Need for the Job and Where to Get It

You need balls :D … a large set of tools and plenty of expensive spare parts. 

Required Parts

The first lesson that most many Diesel Merc hobbyists learn in Germany is to love original Mercedes spare parts like the devil loves holy water. The mark-up on genuine parts is so incredible that just obtaining genuine parts for this job will cost more than the residual value of your car. Being German and knowing the affordable German sources, I got most of the parts from Germany at a fraction of the dealership cost. The problem, you will have anywhere outside of Germany is that vintage Mercs are not so popular, so you will eventually be forced to buy genuine parts or invest a fraction of your repair budged into a German language course and use my sources. Please note that the part numbers used will certainly differ for North American or other Merc models. I can highly recommend the parts catalogue of the Mercedes-Benz club Russia (growing up in East Germany, having learned Russian as a second foreign language, actually pays off in this case). The catalogue itself is mostly in English.

Below you will find the schematic of the required parts and the part numbers for my Model (1989 Mercedes 190D Europe, model 201.122).

Qty	OEM Nr	Description	Source	Tot. Price
2	201 350 80 10	rear axle shaft	Ebay (USA)	463.98 USD
12	001 990 92 12	Screw, transaxle to axle shaft (*)	Mercedes	43.20 CAD
2	202 350 34 08	rear bushings subframe	Taxiteile Berlin, GER	10.00 EUR
2	124 350 03 41	front bushings subframe	Taxiteile Berlin, GER	10.00 EUR
2	201 990 03 04	Screw, rear bushing to body	Mercedes	6.00 CAD
2	914125 5012238	Screw, front bush. to body	Mercedes	6.00 CAD
1	000912 2010181	Screw, transaxle to subframe	Mercedes	3.00 CAD
1	910113 3010002	Nut, transaxle to subframe	Mercedes	3.00 CAD
4	201 990 10 01	Screw, transaxle to subframe	Mercedes	11.48 CAD
2	201 351 00 73	Lock, screws to subframe (not available anymore)	Build yourself (misuse washers)	0
2	202 980 00 16	Wheel bearing repair kit	MKG, Germany	17.47 EUR
2	220 352 02 27	Control arm joint on wheel carrier	MKG, Germany	28.56 EUR
2	124 350 67 06	Fastener kit, control arm	MKG, Germany	10.56 EUR
2	210 350 00 29	Trust arm	MKG, Germany	(**) 98.32 EUR
2	210 350 21 53	Tie rod kit	MKG, Germany	(**)
2	140 350 11 70	Tie rod fasteners to subframe	MKG, Germany	12.56 EUR
2	210 350 33 06	Struts	MKG, Germany	(**)
2	124 350 68 06	Strut fastener kit	MKG, Germany	7.14 EUR
2	210 350 34 06	Camber strut	MKG, Germany	(**)
4	124 350 65 06	Trust arm, camber struts fastener kit (***)	MKG, Germany	14.28 EUR
2	201 420 07 85	Brake cable	Mercedes	65.80 CAD
2	115 993 03 25	Lock Brake cable to body	Mercedes	12.18 CAD
1	126 993 02 10	Hand Brake Spring	Mercedes	9.45 CAD
3	124 990 37 01	Screws, propeller shaft to transaxle	Mercedes	10.80 CAD
3	124 990 14 51	Nuts, propeller shaft to transaxle	Mercedes	6.81 CAD

(*) Those screws come with the wheel bearing repair kit, unfortunately in my case in such a poor quality, that I had to get new ones.
(**) came as set.

Here the explosion diagram of the assemblies, the required parts are marked red.

Here is a good one: Go to Merc and get a quote on the whole list of parts. You end up paying multiples of your cars current value. 

But still for the fasteners, the Mercedes dealerships shave you. If you reuse the old screws, you always risk introducing rust nests or putting weak worn out screws back. After 21 years of serving some of them have reached the legal limit and should be replaced. The original Merc manual always states to use new screws. In addition most body shops I knew in Germany would always use new screws. In my case I actually forgot to buy some of the fasteners (***) from MKG and had to buy them for 8x the price from Mercedes.

Here are the links for my inside sources:

• MKG - Motor Teile Koeln (in German, intl. shipping upon request)
  If you have a genuine German car, they got all the parts… I mean you can get almost everything there. It is not necessarily the cheapest place in Germany, but probably the most versatile there. Unfortunately, you are out of luck if you do not speak German. Upon request, they may consider sending stuff outside the European Union. I usually order stuff locally when I visit and bring the parts to Canada myself.
• Taxiteile Berlin (in German, only ships within Europe)
  A taxi parts store. They offer all “consumables” for any Diesel Merc model that was used as Taxi (W123: 200D, 240D, 300D; W124: 200D, 250D; W201: 2.0D, 2.5D). Fortunately (and decidedly) my 190D is the equivalent of the German Taxi edition. So I can get most of the parts there. If you get a Mercedes part there, you can be almost assured that no one else worldwide can beat their price. Apart from the above parts, you also get excellent deals on various filters, alternators and other stuff. The first thing I do, after I land in Berlin Tegel to visit my family is to visit that store and stack the consumables for the next half year. If I forget something, my cousin usually gets it there and sends it internationally to Canada. Even then you can be assured to be cheaper with shipping than buying the genuine part from Mercedes in Canada.
• Race-Corner (my cousin in Germany, he is also supplier of affordable specialized tools... he got me the torque multiplier gear, that would probably cost outrageous amounts anywhere else). He can get everything that BGS manufactures. Ask him for a price list and international shipping. Some of you may also be interested in his supply of tuning and performance parts.

Local (North-American sources):

• eBay svauto
  US-based dealer of vintage Merc parts.
• Victoria Star Motors Kitchener (my Mercedes-Benz dealership)
  Loved (well it’s the local source of genuine parts) and hated (it’s damn expensive) local Mercedes-Benz dealership.

The parts are actually in many instances comparable to the genuine parts quality. In many instances you actually end up the same part that Mercedes would sell you, but in a different package. Most of these parts are actually still made in Germany.

Things that also could have been done, but weren’t done due to time constraints would be replacing the brake lines and fuel lines. With the sub frame removed, you will have excellent access to those ones. This will be another blog entry.

Tools

Basics (things you should usually have, when maintaining your car)

• Socket and Ratchet kit 3/8in 8 – 19mm
• Combination Socket set 8mm – 32mm
• Torque Wrench at least up to 200 NM
• Pry bar
• Solid Breaker Bar for 1/2in sockets. Something for the tough bolts. This should withstand substantial violence, since most of the screws will be super tight. In my case I also got an additional 1.5m copper tube that I stick on it to force stuff off.
• Hammer with assorted chisels
• Assorted pliers
• Impact Wrench (mine is electric) with at least 17mm, 19mm, and 22mm sockets
  I got the set and an additional 17mm socket from Canadian Tire. This one should output at least 300 – 400 NM of power to be effective (i.e., don’t get the cheap rechargeable ones from Canadian Tire)
• Angle Grinder with extra-thin cutting disks
  I got mine from Canadian Tire and I got extra thin Bosh Piranha cutting disks from Germany. Alternatively a metal saw will do.

Drill-Hammer with HSS- or titanium-coated drill bits and a metal brush to remove rust.

Specialty Tools

• Canadian Tires’ Ball- and U-Joint Set (25-6316-06)
  I (mis-)used that tool to get the rear axle bushings in.
• Torque multiplier gear or torque wrench up to 350 NM.
  I still had a torque multiplier gear from Germany that outputs about 1000 NM of torque and gets almost every tough nut loose or destroys related sockets (whatever is weaker).
• Optional: Coil spring compressor. Mine didn’t fit the rear wheel, so I ended up doing the unsafe removal described below. The original Mercedes compressor that actually fits the rear springs is also outrageously expensive.

If you want to replace the wheel bearings yourself, which I tried but failed to do:

• Wheel hub removal tool that specifically works for Mercedes.
  I got the wrong universal one from Canadian Tire and found that out only half-way through the job. What allegedly works best is the B90 from Sir Tools. Although this tool is very expensive, if you compare the cost of a Canadian Machine shop, you still gain by doing it yourself twice in a lifetime.
• Hydraulic press. To get the bearings back in. Allegedly, this is the easy part, but since I didn’t get the stuff out in the first place, I cannot comment on the repair.
• Mercedes Specialty Bushing tool: This one gets the rubber bushings out of the control arm and wheel carrier. Allegedly, this is a not so hard job as well, but I didn’t do it.

If things go really wrong and you cannot get critical screws out. Trust me; if you think everything is a breeze, fate will eventually hit you hard.

• So find some guy with an oxy-acetylene torch that you can call if things go wrong. This guy can also be used to burn the old rubber bushings out of the subframe. Trust me in my case a propane torch would not help.

Consumables

• Sand paper
• 5 cans of rust paint
• 3 cans of asphalt under body coating
• Fertan rust converter (or any brand of your flavour)
• WD40
• A can bearing grease (for the bearings, but also for the subframe bushings)

Day 1: Preparations

Before you jack up the car, you need to loosen the Axle nuts. Those nuts are wedged onto the axle. Use a chisel to remove the edge that prevents the nuts from turning. Now use a really really long extension or a torque multiplier gear (see picture) to turn the nut.

As shown below my torque gear actually managed to destroy a ½ adapter. So if nothing else helps, pure ignorance and violence will do it. In my case I finally drilled it out and had to re-sharpen the drill bits several times during the process. Those guys used some tough steel in 1989.

 Hours later: Yay! It is out; and nightfall ended day one of the repairs.

Day 2

Now you can finally jack-up your ride. Take off the rear wheels and soak the screws of the rear callipers in WD40. 

First take off the calliper, the two rear screws. Then take off the brake line. Put something to catch the residual brake fluid.

Now the brake disk is almost free. Take out the centering screw that still holds the disk in place and force it off. A few strikes with the hammer work best. Now take the handbrake assembly apart. Those springs will also keep you entertained for quite a while. To avoid further leakage and avoid anything getting inside the brake line, have it covered as shown in the picture. Nightfall again ended day two of the repairs.

Day 3: wasted

Precious time was wasted with the wrong hub-removal tool that would not get the hub off. If you would have the right tool (as stated above) you might have had more success.

Day 4

Now that you have removed the handbrake assembly, you can loosen the three screws that still hold the shield in place. This is very tricky because they are inverted hex and one of them in my case was worn out. Again, precious time was blown away trying to drill the screw out.

With some force and slight hammer strokes you can get that shield loose. Once it is loose, you can rotate it and easily access all the rod joints. I started with the stabilizer and then worked all my way around the rods. The track rod was tricky and would not come out of the wheel assembly, so I finally cut it off.

Day 5

Once you secured the spring or, as shown in my case, put a jack securely below the control arm, you can loosen the control arm joint.

As a side note, I tried to remove the driveshaft now. Unfortunately, the screws to the transaxle were so tight that I had to let them in and have that fixed later. Being under the car I started to remove the propeller-shaft screws already. Next you need to loosen the propeller shaft bearing assembly such that you can slightly compress the propeller shaft and push it out of the transaxle.

Using a puller, we pushed the axle out of the hub and finally took the wheel assembly off.

Once you removed the strut bolts, you can carefully lower the jack and take out the spring. This is the redneck variant. Any serious shop would usually secure the spring before doing it. If it goes wrong, the spring with all its force lands right in your face.

Day 6

After some thinking about how to take the axle frame out, I decided to use a three point connection. A large jack would be positioned under the transaxle and a two-by-four on two jacks would secure the front of the frame from falling down.

Now loosen the four subframe screws and triple-check that there is nothing else in the way of the subframe. You guys, who drive a 190E (the gas model) will eventually have to worry about the fuel pump and other stuff attached to the subframe. The whole exhaust has also been removed already.

Once the whole thing is down, you can use the trolley-jack and pull it out from under the car. Congratulations, you’re almost half-way there.

Day 7: Shopping day

Because my ½ in adapter from the torque multiplier was gone and the shape of the nuts drive-shaft to transaxle has changed from XZN to inverted TORX, I needed to get some specialty tools. In Germany, you would go to BGS or Hazet and be served right away. Here in Canada, finding a proper supplier became a little odyssey. The mainstream Canadian shops, like Canadian-Tire do not carry such sockets. Finally, we ended up getting the XZN Socket from Spaenaur, Kitchener, ON and the ½ - ¾ in adapter from Horsefall Auto parts. We also got some of the missing screws and brake cables from the local Merc dealership.

Day 8

We still had to get the old rear axle bushings out of the subframe and the tight bolts out that connected the axles to the transaxle. My friend knows a local Mechanic who usually works on classic cars, who offered to help with his acetylene troche and a pressure hammer. 

With ignorance, a torch and excessive force we were able to get the bolts out. If you actually try to dare that at home cool the connector wheel of the transaxle. If the heat goes inside the transaxle, all your transaxle seals will melt and you will have to pay LOTS $ for having the seals replaced and your transaxle play adjusted. Unfortunately, you have to put the entire transaxle into pieces to get to these seals (that is certainly not a hobbyist job). So far we were lucky and they have not appeared to be leaking.

After setting the bushings on fire and trying to wedge them out with a pressure hammer, we could get the remains out with a three-arm puller out of the subframe.

Allegedly, this is supposed to be an easy job and the bushings should slip out like a breeze… well experience proved this myth wrong. 120 CAD and 1.5h later the stuff was out. Fair price, considering us showing up on a weekend while he was currently allocated with building a new shop for his dog.

In addition we still had the wheel carriers with the rubber bushings, hubs and wheel bearings. That needed to go out. Unfortunately, Jim did not have a large enough press to get the stuff out, so we were looking somewhere else.
By the way, many thanks to Jim Struke in New Dundee for the help. Otherwise, I would have spend lots of fruitless effort in trying to get the stuff out.

Day 9

Outdoor mechanical work was suspended due to severe weather.  No one wants to lie in the mud in stormy weather. Instead the time was put to use to turn the storage room into a mess with spray paint. Having all the parts in pieces allows you to rustproof everything and conserve it for next few years. Using fire truck rust paint makes it also look like a racing suspension (yes, what a scam for a 75 hp Diesel Merc).

I was also investigating sandblasting as an option to clear the subframe. Some of the corners cannot be easily reached with a Dremel or angle grinder. However, such jobs seem to be outrageously expensive in this area and second the only guys who would have done that were booked out for the next few weeks. The guys who do this in Kitcherner Ontario were Chiefs Heavy Truck Collisions Centre and Reizels. Chiefs quoted about 200 CAD for just sanding the frame over the phone. Instead, I removed the rust as best as I could and soaked the remains in Fertan. Finally, I applied a thick coat of rust paint and after the paint was dry painted big stripes of bearing grease on the welds and corners where the grinder could not go in the first place.

No pictures: At the same day we also started a little Odyssey to find someone with a large enough hydraulic press and skill to get the bushings in the control arm, wheel carrier and the bearings replaced. We finally ended going to Heimpel Automotive in Kitchener. Those guys got everything fixed for 225 CAD in total. Adding up the individual cost, I am actually reflecting if buying the special tool and a hydraulic press could have saved money in the long run.

Day 10, 11, and 12: On-car rust proofing days

Having the subframe out gives easy access to all the rust spots under the car. First the whole rust was carefully with a rotating wire brush. Then the entire surface was “cold-galvanized” using Fertan rust converter. This stuff has to sit 24 hours to rust-proof the surface. 
The next day we removed the excessive Fertan and started soaking the remains in rust paint.

On the last day I applied a thick coat of rubberized asphalt under body coating. To make sure, that I do not have to worry about rust this area for the next 20 years.

Since some of the spacers and screws were actually reused, I also cleaned them while the underbody coating was getting dry.

Day 13 and 14

Now that everything was dry and prepared we could finally begin putting the subframe back together. The first task was to push in the new rubber bushings into the subframe. We (mis-)used a ball joint tool that was borrowed from Canadian Tire. To make it slip, bearing grease was applied.

Next we attached the transaxle back to the subframe. All the screws get tightened with a torque of 70 NM. Do not forget the spacer for the front bolt of the transaxle; otherwise, you have to worry about heavy vibrations while driving.

Now the same technique that we used to get the frame out in the first place, was used to put it back in. Then the frame was mounted up. These screws get a torque of approximately 80 - 100 NM as well.

Now gather all the required parts, screws and stuff to get the wheel assembly back together. 

First start by putting the control arm back into the frame (do not tighten the bolts yet). Now you can use the redneck trick again to get the spring in. Once you put in the bolt of the strut the assembly is more or less (redneck-) secure.

Now we got started on all the rods. Unfortunately, some of the new rods did not have the spacers, so we had to salvage some of the old rods’ spacers. Turns out that one of the rods did not fit the screw, so force needed to be used.

Now put in all the rods to the subframe.

With all the rods in place and loosely connected to the subframe, you can start working on the axle.

Once the axle is in place you can push the wheel carrier onto the axle and start assembling the rest. In our case the machine shop made a couple small dents into the hub edge (again a good indication that I should have probably got the tools and did the job myself. The job looked a bit sloppy for 225 CAD). So we had to use a rubber-hammer to force the wheel carrier onto the axle.

Now that everything is in place, loosely connect the rods to the carrier (do not tight it down) and also connect the carrier to the control arm (do not tight down).

The trick to have an almost aligned track is now to use the jack and jack up the control arm until the axle appears to be 100% horizontal. In this position tighten down all the bolts: 75 NM for all rod bolts, except track rod, the nut only gets on with 40 NM. The connections to the subframe are a tight mess. I could not wedge a torque wrench in there and just tightened the stuff down as much as I could. The big screws for the control arm get tightened down with 120 NM. The strut nuts are at 40 NM.

Once that is done, you can have fun with the handbrake assembly again. First tighten down those three bolds that hold the shield in place (25 NM). In addition, the shield may be deformed so a crow bar might be necessary to get it back into its original shape. Now have fun with the handbrake assembly.

The tick is to get the upper half of the handbrake shoes connected with the spring. Then wedge those two halves over the hub and try to get the other spring in. If you replace the handbrake cables, as we did, you may have to lock the cable in place first.

Once the handbrake is in place again, clean the hub throughout and apply heat-resistant grease (I used calliper lube) on the hub. That will prevent rusting the brake disk to the hub. If this happens, you are really fucked the next time you need to replace the disks.

Now stick the brake disk back on, put the callipers back. Since the entire wheel assembly was red, I also decided to put some calliper paint on. That will look nice in the spring again, when I have my Ronal Rims back on. Tighten the calliper bolts down with 70 NM.

Now things turned really late and I did not take further pictures. But here is what happens next.

With the handbrake in place you can now tighten down all the bolts that connect the transaxle.

First put in the bolts that connect the propeller shaft to the transaxle. They get tightened down at 40 NM. You will also have to put the drive shaft bearing back in place.

Next tighten down the bolts that connect the drive shafts to the transaxle, they get tightened down with 75 NM each. Because the axle will turn, you can always have some apply the handbrake first, then tighten the screw, remove the handbrake and then worry about the next screw. That will keep you busy for a while.

Now you can bleed the brakes and already put the beer in the fridge, because you are almost done.

Once this is done, put the wheels back on and lower the car. Now the final mess is to tighten the drive shaft bolts again. They require 350 + 20 NM. You will not find a standard torque wrench that big. In my case I still had the torque multiplier gear and could approximately match the torque. A redneck version would be to tighten the bolt with about 200 NM (i.e. standard torque wrench maximum) and then get a big extension. With that extension turn this screw again by about 45 degrees. To be really sure that this thing does not come off anymore, peen the edge of the nut down to match the spaces in the axle (see the first picture how the original one looked like).

Now get that beer, celebrate (!) and take your ride to an axle alignment for the next few days.

Conclusion

Well the axle is back together, the car goes straight and the noise has disappeared. It actually worked. The original schedule was way to optimistic for the repair and in addition to costing much more than anticipated this job also put some of my other projects at risk. This job was certainly not as easy as many people proclaimed it would be.

I would also like to use this opportunity to thank Hans for being able to use his driveway for the repairs and his excellent care when it came to hot beverages and supplying some of the required special tools. He also provided me with insight knowledge of the machine shops and helped me getting some of the parts and tools and helped out with transporting the stuff around. Without that help, the job would have been close to infeasible.

Most of the time wasted was spend on organization and commuting. Not having your own repair place will end up costing you significant amounts of time to commute to your repair location. If in addition to that, you forgot some of the required tools this will really mess up your schedule. The four day estimate given by fellow mechanics in Germany, assumes the availability of a specialized shops. Day one would be spent on disassembly. Day two and three would be spent rust-proofing, waiting for the paint/coating to get dry, and used for the machine shop works (bearings, bushings etc). Day four would be the entire assembly again and wheel alignment. In Germany specialized shops and Mercedes parts are also much easier and faster to get than Canada so even minor set backs could be accommodated in that timeframe. If you do not have that luxury to live in Germany and still want to do it yourself quadruple this estimate, because things will go wrong and getting help then will end up costing you lots of time. Especially if you are in my situation: are PhD student in Canada, do not have your own garage, have an ambitious ongoing course project, TA an operating systems course, have to attend two conferences, and spend 12 hours of martial arts training each week (6h Kendo and 6h of Karate in my case)… you will regret it!

Next time, I have to do that. The job will be well planned in advance. I hope by the time the subframe wears out again (maybe in 10 – 20 years); I will have my own full equipped garage and could do this job more efficiently. Here some impressions of the good old days...