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10-25-2002, 01:04 AM
Question was asked:
What are the possible reasons that BMW would put more play than normal into the M3 driveline? Maybe as an engineer you can answer this.

I would love to take the drive line apart and investigate. Without seeing the design and manufacturing it would only be speculation as to why there is "too much" play or clearance in the assembly(s).

I can't understand why there would be excessive clearance. It would be understandable if this were due to temperature changes. For instance, the valve train in the excessively loose when cold, but the clearance tightens up when the engine comes up to normal operating temperature. But this is not the case in the differential. Or if the clearances change appreciably in the differential, then the engineer erred because the noise we hear is noticable at all temperatures, cold and hot, or normal.

One dealer told me the noise was from the flywheel. Another dealer told me it was from the rear end. I tend to believe it is from the rear end at this point, because I read a copy of a service bulletin online describing to dealers about the excessive clearance causing noise in the rear end.

I know we have a sophisticated rear end. But I can't understand why it has to rattle the way it does. Granted, none (or only a few) have failed, but I am not suprised. It is robust, no doubt. Some things in cars never seem to fail, while other things do all the time. Brake pads fail or wear out on a regular basis. How often do you have to replace a steering wheel in the life of a car? Never. If your steering wheel was made of cardboard, it would probably have to be replaced every few days. Would you agree? So the rear end parts are robust and will probably never need replacing, but with excessive backlash, or clearance somewhere, it is making noise and will continue to. The noise may or may not be detrimental. Regardless, it is annoying and in my estimation, without further investigation, unnecessary.

BMW has done nothing to fix this problem, and I am not suprised. It would be a huge undertaking and costly. So without incentive to fix all the noisy M3's, most may suffer this defect for the lives of their cars. The engineers at BMW have probably looked at this and determined that the rear ends will probably last at least 50,000 miles, and there is no safety liability (i.e., none will blow apart), therefore, nothing needs to be done.

In the meantime, I wish I had an extra M3 sitting around to dismantle. I would like to investigate. Or maybe a class action by all M3 owners would get some attention. Is there a lawyer reading this? Give me a call.

Some recalls are pretty inexpensive. The defect we have in the fuel injection system causing cold start problems for some (me included) will probably be an easy software upgrade at some point. But the rear end fix...can you imagine? Based on my experience at the dealership, well.....they couldn't even replace a flat tire without screwing it up. Seriously...they didn't even use the correct socket for the lug nuts and scratched up a brand new wheel! I'd never even dream of them taking apart the rear end.

I love the way the M3 drives. I don't like the noise. Maybe I am more conditioned to dislike it because it is my belief, based on years of experience in the field of mechanical engineering and machinery maintenance, that a mistake was made in engineering or manufacture and it should, and can be remedied. JP

10-25-2002, 06:49 AM
My dad has a tricked out Mustang built by famed Mustang builder Kenny Brown. I drove this car and immediately noticed the rear end makes the exact same clunk noises as my M3 rear end. I suspect BMW and Kenny Brown use some kind of high performance rear end that has this trait by nature due to the features of the rear end.

10-25-2002, 07:41 AM
<a href="">New diff and rear axle carrier in production from 02/02</a>

<img src="">

10-25-2002, 11:33 AM
i have studied the new part schematic with some very knowledgable gents - we all seem to conclude is the identical carrier - no apparent change at all; i have also inquired regarding this part and the factory says it is the same exact carrier; the '03's & the ;02's clunk which has very little to do with the carrier assembly anyway; the spooled up backlash from the diffy, the nature of the driveline & the clutch all contribute to the wonderful harmonics we get as a bonus of owning these great state-of-the-art cars. Seems the engineers love the driveline so much they have found no need to change the basic approach much since the early '70's - when faced with the torque from this diffy along with the power of the engine & the need to augment the clutch/flywheel they simply allow a more tolerant geometry to absorb the forces. what we get is clunk...clunk,clunk...clunk. even the MCoupe will clunk for you if you declutch at low speed, just not as dramatic as the driveline is much shorter.

10-25-2002, 04:15 PM
If it's the exact same parts, why new partnumbers for the diff and the rear axle carrier from 02/02 then?

Look in the columns "From" and "Up To". The new parts are highlighted in blue in the pics.

The EPC database also says the parts are "exchangeable retroeffective".


10-25-2002, 04:19 PM
I thought we had a very sophisticated torque shifting super duper design. WOW. Maybe Ford has a better idea afterall!

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