Please help with clunk noise

[grandmaster]

Hi,

We have a 2000 328CI with the steptronic transmission which is a GM 5 made in France.

The car makes a clunk noise when accelerating or tapping on the brakes at low speed (under 20mph) and coming to a stop. It sounds like the noise comes from the rear driver side. So far we have replaced the rear trail arm bushings. Changed the diff fluid and had it inspected. Replaced the drive shaft. And finally, installed the new output flange kit from the service bulletin which seemed to describe the symptoms to a tee. The final thing we had done was erase the transmissions memory which learns how you drive and shifts accordingly.

Also, the car will NOT clunk in neutral. So if you go in N, hit the brakes and come to a stop there is no clunk. Nor in Reverse gear either. So it's not a loose bushing, or strut etc. It only happens when in gear, and in 1st gear from what we can tell... and only when hitting or letting off the gas, or coming to a stop. Maybe a 2-1 shift, or vice versa...

We are lost now as the clunk is still there. Sometimes it doesn't happen until you drive the car for about 1 or 2 minutes... it will be perfect.. but then start after a small time period of driving.

Should we:
-Change the transmission oil?
-Replace the differential?
-Reprogram the transmission software?

Can someone please shed some help on what reprogramming the tranmission means or what can we tell/ask the mechanic since he has no idea other than how to clear the tranny memory and read codes.

Any help is greatly appreciated.

[BMWJNKY]

Have you put a new diff mount in it?

[grandmaster]

No. Never thought about that. What does the mount consist of? Is there a way to check it and what should a person look for / test?

The car has 50K miles and never driven hard.

[kingo328]

Rear diff mount:
See fig 7 in this link:
Differential DYI instructions - E46Fanatics

Also see item 9 in this link:
RealOEM.COM * BMW E46 328i REAR AXLE CARRIER

The bushing itself is about $30. Labor is the killer. Diff must be removed, then old bushing pressed out, new one pressed in and diff installed. I've heard of quotes between $300 and $800. With all the other work you have had done, I'm surprised no one mentioned the rear diff mount.

This link shows a bad bushing (it also shows subframe damage....not pretty):
Whats bad about it is the rubber part is torn. The hole is supposed to be oval shapped.
Another one bites the dust: rear subframe damage - E46Fanatics

Note: If you are unlucky enuf to have a torn or damaged subframe, make sure you go here:
Girard Gibbs LLP - Investigation of BMW

I've done a lot of reading on this subject in the last couple of weeks because I have the same problem and am determined to find the cause. All other threads that bring up this issue just die out with no resolution. Some say "its normal", I dont buy it. Some say "all high mileage cars have funny noises, live with it". True, but they can be fixed. I havent heard of a for sure fix for this problem.

The one component that has not been mentioned in all the threads I have read is the differential itself. Diff bushings, suspension bushings, subframe bushings, trans output flange....all these things have been mentioned. In some cases replacing the rear diff bushing helped, in other cases it did not. The same is true for the other parts just mentioned. But I have not read one post that said the repair eliminated the noise completely and permanently (permanently=until the offending part wears out again). Again, no one has mentioned the differential itself.

I'd like to hear from someone that has replaced their diff in an attmept to fix this problem.

[FL325i]

Our clunk in the rear on decel, approaching a stop, was solved with a reprogram of the tranny.

[grandmaster]

Hi Kingo,

So far we have inspected everything except the differential mount and differential bushings. Hopefully we will do this soon but from what I understand you have to drop the differential and it's time consuming and expensive. Problem is, the thud only occurs on what seems to be a 2-1 downshift and when you hit the gas, or let off the gas at a slow speed. Never in neutral or going into reverse. But, i've heard that the 1st and 2nd gear seem to have lots of torque which get transfered to the rear and cause lots of torsion.

[grandmaster]

Hi FL325i,

What symptoms did you have other than a clunk coming to a stop? What about hitting the gas, or letting off the gas at slower speeds?

[e46_andy]

my car does that too! i think since the steptronic tranny holds the gear until u go soo fast when u let off the gas (around 10-15 mph) you hear it... also when you brake... i have a friend that also has the problem, she has a 2006 325i... BTW i have a 1999 328i

[wfuerte328i]

i happened to find an ad link to this website that describes a major defect on 3 series, at first it seemed like bs, but i crawled under my car, and ive got the same problem. check out this link...
BMW 3 Series Defect - Subframe Crack - Law Firm Wasserman, Comden & Casselman, LLP Attorneys Tarzana, California