Preparing BK02837 (M5 3.6) for another twenty years. - Page 2 - BMW M5 Forum and M6 Forums
E34 M5 Discussion 1988-1995 Sedan and Touring

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post #11 of 111 Old 6th April 2012, 09:17 AM
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Looking good so far!

The corrosion underneath is rather alarming, good that you're sorting it out. Is that normal for cars that age in the UK and US?
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post #12 of 111 Old 6th April 2012, 10:14 AM
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No, its actually very low on rust.

Many UK M5's have suffered from the brown devil extensively.

The e34 started to rust only a few years ago.. I had many many E34's and never any rust with any make or model, untill 2004/5/6 , I just saw it emerging on client and my own E34's.

Pretty strange.

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post #13 of 111 Old 6th April 2012, 10:41 AM
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Thanks Wout.

I too have seen shocking pics before. I guess I'm lucky being in the part of the word I am, there's not very much rust on my E34 and the rust on my other cars has been pretty minimal.

I must say that having just done a 98% suspension replacement (only thing not changed was SLS lines to the pump, the pump and the front struts (to which the inserts mount) it was well worth it!
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post #14 of 111 Old 5th May 2012, 10:13 PM Thread Starter
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Throughout March, I completed the preservation of the left front fender and its sandwich construction to the sills. About two weeks ago, it was time to remove the right front fender to do the same for the right side.

The front fender is in similar condition as the left example; there is some surface rust, but nothing that a good clean and a rust converter can’t solve.

I forgot to make a picture of the condition of the right-front jackstand prior to cleaning them, but just like on the front-left example, its protective coating got damaged throughout the years and as a result were slightly corroded. They were brushed with a few appropriate dremel-tools in order to remove the remnants of the coating and clean the cavities without removing any solid-metal (as is the case with plain sanding).

Before applying the primer coat, the surface was cleaned with a degreasing solvent and etching fluid from POR15; the etching fluid was given a few days of curing time before the final primer-coat was applied. I usually apply three thin coats, but the following picture shows the intermediate result of just two; the second layer was applied after the first layer dried enough to be in a tacky-state.

For some time, the rear wheels of BK02837 was a little too low. Although this filled the wheel-arches nicely, the ride was too harsh. This usually is caused by the pressure accumulators of the SLS-system. Each accumulator contains a membrane to regulate the pressure through the shock-absorbers. This membrane is made from rubber that is subject to wear and aging. At some point, the two chambers in the accumulators are connected due to which the shock-absorbers are subject to the full pressure of the SLS system that is fed by the PAS-pump at the front-left side of the engine.

The shock absorbers were replaced in 2006 at a considerable expense, but have been used for no more than 25k km since then so are still new. Besides, their retail price has increased to more than 700 Euro’s each; needless to say that I don’t want to take any risk of ruining them. Besides, I like the composed suspension of the E34 that despite using low-profile 17” tires isn’t overly harsh and thus offers some comfort on long distance trips without compromising on predictability. Next to originality, that was an important reason for me to stick to the OE suspension in July 2006.

The removal of the SLS-accumulators is rather straight forward. These are bolted to the body with three M6 bolts. The access to the rear-bolt is limited, especially on the left side where the exhaust limits space, but nothing that a few extension tools cannot solve. Care should be taken when disconnecting the ingoing and outgoing pressure lines. A simple half-open wrench won’t do as it doesn’t distribute the force evenly around the nut due to which it will just damage. Instead, I used a half-open hexagonal wrench, a much better tool for the job.

Since the pressure hoses between the SLS-accumulators and shock absorbers are replaced as well, I did not disconnect the outgoing connection directly on the accumulators, but on the shock absorbers instead. This requires two 17mm wrenches; one to secure the ingoing connector to the shock-absorber and the other two disconnect the nut from the pressure-hose. The right accumulator just drops out; the left one, requires lifting of the car to gain enough clearance between the exhaust and the drive-shaft.

After removal, the condition of the underlying body can be assessed, which apart from being a bit dirty is excellent. There is no rust and/or damage anywhere which is typical for a car that has never been used as a daily driver and also has never been subject to winter-usage.

Although not really necessary, I replaced the rubber mounts, bolts and nuts as well. The right accumulator is in place; the left one is still a to do item as well as the hoses.

Hopefully, this will solve the harsh ride, but I will know that for certain later this year. I would like to send the steering-box for a rebuild as well and since both systems are supplied with pressure by the same pump, I won’t fill the reservoir for the power-steering until-that is completed.

In between all this work, I found some time to fill the final drive with some new lubricant as well. On Limited slip differential’s such as used on the E34 M5, I prefer Castrol SAF-XJ which is rated with a viscosity of 75W140.

I used to buy this from the dealer, but at hefty price-tag of around 70Euro’s per litre. On ‘fleebay’, the same product is offered for just 12 Euro per liter, which is significantly less, but not always ‘fresh’ as being from recent production. Please note that Castrol recently relabeled SAF-XJ to
‘Limited Slip 75W140’. Despite the name-change, this is the same product.


==> MY90 E34 M5 3.6 <==
==> MY85 E28 M5 M88/3 <==

The E34 M5 Alps tour. Sixth edition: 14-17 September 2007

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post #15 of 111 Old 13th May 2012, 06:25 PM Thread Starter
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The removal of the left pressure accumulator is not as straightforward. It cannot be removed without lowering the exhaust system or lifting the rear-wheels. Lowering the exhaust gains the best access and the unit will simply drop out, but the exhaust system itself is very heavy and is a two-man job, a little too much for the replacement of the accumulators.

Warning : Do not try to do this on your own driveway without taking appropriate safety measures. After all, we are dealing with a car weighing in excess of 1700kg.

I always use high-quality tools. In this particular case, this applies to the half-open 11mm hexagonal wrench for loosening and tightening the nuts of the pipe-work to the accumulators. A simple half-open wrench will only damage the nuts, resulting in a much more difficult repair job.

Lifting the rear-suspension is most convenient, but even them there is only one way to maneuver the old accumulator out of the car. This is then only possible because of the increased space between the driveshaft and the bodywork, just enough for its removal through the gap between the driveshaft, the chassis and the rear-damper of the exhaust.

After removal, I inspected the bodywork which is in excellent condition. This also applies to the brake, fuel and SLS-lines. I might replace the two hoses from the SLS-feed and return lines, but to be honest that is only for cosmetic purposes. Before placing the new accumulators, I replaced the rubber suspension mounts as well. The protective cover was cleaned and reused; there was no need to buy a new one.

The most difficult part in the process is the bolt with which the left-accumulator is bolted to the chassis on its rear. The space is constrained and there is hardly any room for two hands. In fact, I had to turn in the bolt manually whilst aligning the accumulator to its fixing position on the chassis. It took four-or five attempts before the bolt finally turned in and that was with the car a proper hoist with enough working space underneath

With the left accumulator in place, the connections to the self-leveling system has to be established. At first, I reconnected the feeder lines. Just like the steel fuel and brake lines, these are in excellent condition and only need a mild-clean before applying the final protective coating of white-ML.

Since the hoses between the shock-absorber and the accumulators are twenty-two years of age during which they had to endure the hardship of driving most part of its 190k km in the Alps and some laps on the Nurburgring Nordschleife as well, these are replaced with new parts.

I started with the connection of the hoses to the shock-absorbers before connecting them to the accumulators.

The threaded nuts were turned in manually to avoid damage to the inserts on the accumulators and the expensive shock absorbers. Final tightening will be done with an half-open 15mm wrench (accumulators) and half-open 17mm wrench (shock-absorbers)

Remains the disposal of the old parts and the hydraulic oil that was drained. The hoses will be kept for future reference in the case that BMW might declare them NLA.

With both sides having new pressure accumulators, one can fill the hydraulic reservoir for the power steering, but as I intend to remove the steering-gearbox for a replacement or overhaul, this will be done afterwards.


==> MY90 E34 M5 3.6 <==
==> MY85 E28 M5 M88/3 <==

The E34 M5 Alps tour. Sixth edition: 14-17 September 2007

Last edited by raymondw; 13th May 2012 at 06:30 PM.
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post #16 of 111 Old 15th May 2012, 04:57 AM
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Fantastic thread. My car is going through a mini 20 year revival also so thanks for pointing out the areas of corrosion to look out for
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post #17 of 111 Old 15th May 2012, 12:20 PM
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Excellent thread! Hungry for more

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post #18 of 111 Old 15th May 2012, 10:02 PM Thread Starter
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The original plan was to start with the cosmetic overhaul including preserving the front jack-stands and lower sills. This includes some repainting as well. Whilst replacing the pressure accumulators for the self-leveling suspension, I started thinking about priorities. Originally, I wanted to complete the cosmetic project as soon as possible, for which I have to top-up the hydraulic reservoir with about one liter of Pentosin. As I want to rebuild the steering-gearbox as well, I have to drain the Pentosin again, which doesn’t make sense.

Therefore, I changed my planning. The next step will be the removal of the steering-gearbox. This will be a perfect opportunity to solve the sweating sump-gasket (still original)and the leaking front-crankshaft seal. Whilst the sump is off the car, I can replace the piston-rod bearings shells as well. I do not expect anything wrong with them, but considering its use during my ownership, it doesn’t hurt to replace them.

This requires changing the planning as follows:

1: Preservation of the lower sills and jack-stands => Q1 2012 (done)
2: Replacement of the SLS-system’s pressure accumulators => Q1 2012 (done)
3: Overhaul of the steering-gearbox => Q2 2012
4: Engine work => Q3/Q4 2012
5: Cosmetic work => Q1 2013
6: Engine tune-up and setup => Q2/2013


==> MY90 E34 M5 3.6 <==
==> MY85 E28 M5 M88/3 <==

The E34 M5 Alps tour. Sixth edition: 14-17 September 2007
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post #19 of 111 Old 19th May 2012, 05:58 PM
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Great post and pics as usual , Ray .

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post #20 of 111 Old 10th June 2012, 09:10 PM
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Bump, because this thread has really interesting information, since I am interested in keeping my M5 for a long time as well

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