SteveL

Cross posting from benzworld R170 forum where a reader with a modified SLK32 discovered a problem with his diff when going to install a Kleemann LSD. I thought it was relevant to this forum as well. It would be interesting to know how common this problem is.

http://www.benzworld.org/forums/foru...id=26#M1787979

smgC32

That should happen to any open diff car that builds excessive heat due to extended happy driving!

Cory @ Kleemann

It has nothing to do with excessive heat- the root cause is big HP/TQ and too many smokey burn outs.

smgC32

Are you saying that this would never happen in a low hp/tq car doing smoking burnouts or constant drifting/power sliding? I believe the reference with the SLK owners has to do with powersliding more than burnouts. Ever see the posted vid with the SLK sliding around a constant radius? Or the other car (C or E Class) in a parking lot doing figure eights with light poles as obsticles? Once the car's rear end is hung out, the amount of hp/tq to hold it in a slide is not that great. In therory, if you could hold a slide for hours around a skid pad in a low hp/tq open diff car, the diff would fail, not because of power output, but due to excessive heat buildup. The stronger the diff assembly, the harder it is to break. The weak link I believe is the bushings that surround the shaft in question and that they can't take the heat. We really need to see the other components of that car's diff. Any pics?

Cory @ Kleemann

Again- has nothing to do with excessive heat buildup. The roll pin which retains the pinion shaft in the carrier sheared off, causing the pinion shaft to rotate with the planetary gears. Eventually, during high loading of the Diff- burn outs, drifting, etc., the pinion shaft will eventually start slamming against the carrier and elongate the bore in which the pinion shaft resides- there are no busings in the bore, as the pinion shaft was never meant rotate with the planetary gears.

When this problem is ignored, this is what will happen:

smgC32

I thought there was a bushing that seperated the gear and the shaft. If this was to fail, you would have wear on the shaft similar to what you would find on a crank after spinning a crank shaft bearing. In your pic, did the shaft extend far from its hole or just elongate it and the wear was at the point of insertion in the housing? The previous pics from the other forum show wear an inch or so from the ends where the gear fit onto. Does the gear fit onto the shaft metal to metal? Is that a pic of a SLK diff? It appears to be different than the C32's core. I have had my ECU shut down the car before due to high diff temps caused by excessive wheel spin with the open diff design. Any more pics of an SLK diff to compare to the C32's in order to varify compatibility?

Cory @ Kleemann

No bushings between the pinion shaft and the gears- I can guarantee you this. Keep in mind, ESP is designed to stop wheels spin, which also protects the Diff. By doing a big nasty burn out, one of the small planetary gears is basically spinning on the pinion shaft at very high speeds, which is what is causing the wear on the pinion shaft. If it was caused by excessive heat (don't get me wrong, there is always some amount of heat), there would be telltale signs on the pinion shaft and the gears (discoloration), which there wasn't. The pic I posted was right after I took the carrier out of the differential housing.

There is not any kind of temperature sensor, or any other sensor for that matter in the differential of MB cars, so how can your ECU possibly cut timing/throttle, etc. without at LEAST a temperature input signal from the Diff? The answer is simple- it can't. Are you talking about something other than an MB? Your car shutting down was not caused by Differential overheating. I can do big nasty burn outs in my CLK for hours on end without anything "shutting down"- sounds like you have some other issue if your talking about your C32. Probably excessive inlet temperatures, coupled with high intercooler water temps, due to virtually no airflow and high engine revs- just my .02

smgC32

You may me more knowledgable than me in this arena, and your experience with Kleemann's assembly observations surely show what goes wrong. I am curious how the gears are held together without a bushing and how they don't overheat, metal on metal.

If you are doing hours of burn outs, is this a picture of your diff that broke or is yours OK?

As for overheating and shuting down the ECU, I additionally have heat soak issues with the supercharger that probably can only be solved by manufacturing a custom intercooler that sits on top of the supercharger. The current location of the intercooler prevents heat dissapation at appropriate rates. I feel though that the stock exchanger in the front of the car is more than adequate and twice as large as the one offered by the other company that is getting so much press in another thread at this time.