Clunking noise when coasting - HELP~!

[GQ_Style]

I get a clunking noise whenever I let the car coast. This is a 95 M3 manual tranny. The clunking is SPEED dependent, not RPM dependant. And it only happens whenever I coast, whether clutch engaged or not, as long as I am moving and the foot is off the gas, I get a clunking sound that is speed dependant.

Is this my diff or my axles? My guibo? No issues at all when accelerating hard. Just coasting. The clunking is not too loud, I thought I had a flat spot on my tire but that is NOT the case. Also my speedo stopped working just a week ago. Could it be something fell into my diff? Maybe low on fluid? I can't think of a reason why it would only clunk when coasting and not when engine power is applied. Clunking is heard mosting inside car cabin, I roll down the window and I can't really hear any clunking noise from the outside.

Anybody experience this? Help! Thanks.

[monterey]

sounds like the rear shock mount.

[GQ_Style]

Not as noticeable today. Problem hopefully went away. I'm going t be changing out the diff fluid next weekend. Hope that fixes it.

[Micah D. Cranman]

Yes, it sounds like your Rear Shock Mounts are blown. Do you get a clunking noise over bumps as well?

[GQ_Style]

I just don't understand how a RSM would make this sound going straight, coasting on a smooth road. I always thought I would hear this sound over bumps, which I do not.

[monterey]

rear ends usually make a "howling" noise. pull the carpet back and take a look at the rsm first. I kept doubting my rsm because they were only a few days old when I started hearing the clunk. Sure enough they broke. Dam bilsteins! check your exhaust hangers also. These noises can be most annoying.

[MotorWerkz]

hey GQ_Style .. look at this one:


http://www.germantechnik.com/showthread.php?threadid=36

[JT///M3]

I have this same problem on my 98 M3. I don't think its the RSM b/c I know what that sounds like. Its not what you guys think. The clunk happens when you punch the clutch to let the car cruise in neutral. This usally happens around 5-10mph and only happens sometimes. I was told that it may be the drive shaft. The BMW tech said it may be some play that develops over time. He said he may be adjusted, but sooner or later you will need a new driveshaft...not what I wanted to hear. Let me know if you find anything...

[N311V]

I'm having the same problem in my 97 318is. I can easily reproduce the clunk when coasting in neutral and sometimes when coasting in gear. No clunk when on power and no relation to speed bumps.

I got under the car today and when in neutral I can rotate the drive shaft by hand which produces a clunking noise inside the diff, when I engage a gear I can no longer rotate the drive shaft by hand and get no clunk.

Have I found the clunk noise I get when coasting and if so what do you think is faulty?

[EURO M3 CSL]

I'm having the same problem in my 97 318is. I can easily reproduce the clunk when coasting in neutral and sometimes when coasting in gear. No clunk when on power and no relation to speed bumps.

I got under the car today and when in neutral I can rotate the drive shaft by hand which produces a clunking noise inside the diff, when I engage a gear I can no longer rotate the drive shaft by hand and get no clunk.

Have I found the clunk noise I get when coasting and if so what do you think is faulty?

chances are either the diff has wear on its gearing causing the clunk. Could be low on oil, so u might want to change the oil. if the problem still pursist then its most likely the diff. do u hear a clunk when u turn the rear wheels when its up in the air? when u turn the rear wheel is there a substantial amount of play before the drive shaft moves?

[m3cliff]

Nice revival!

There really was no answer to or outcome from the original poster.

If your speedo suddenly stops working or works intermittently and jumps around, check the speed sensor in the diff. IIRC it's just two 10mm screws. If the sensor is covered with "gunk" that is stuck to it and it looks semi-metallic there is something going wrong inside of your diff.

The same thing happened to me at about 160k.
I got a slight off throttle clunk, nothing really noticeable to passengers, and within 100 miles the speedo stopped working.
When I checked the sensor there was some very fine metal particles all around it.
I cleaned it off, reinstalled it and drove around and the block. The speedo worked but still had the clunk.
Needless to say I opened up the diff and there were all kinds of things wrong inside.
And it never whined or made any noise other than a slight clunking. I was out with car friends when the speedo stopped working and when I told them how messed up it was they couldn't believe that it was still running in the car that day.
Some still think I blew it up doing burnouts or doughnuts, but didn't want to tell them the truth...

[N311V]

chances are either the diff has wear on its gearing causing the clunk. Could be low on oil, so u might want to change the oil. if the problem still pursist then its most likely the diff. do u hear a clunk when u turn the rear wheels when its up in the air? when u turn the rear wheel is there a substantial amount of play before the drive shaft moves?

Is there a trick to changing the diff oil? I can not get a 14mm Allen socket in there as it's too long, fuel tank in the way.

Oddly enough I do not notice a clunk when I turn the wheels. I did notice that my right rear wheel bearing needs replacing though. There is a considerable amount of play at the bearing, I checked this by holding the wheel at 12 and 6 o'clock then shaking. Could this causes play in the axle which translates to the diff and gives me the clunk when coasting?

Do you think the clunk could be this bearing, seems strange to only hear it when coasting or off power at low speed to me, not that I have a clue half the time.

I'll get the car back up and check for play before the drive shaft moves today.

Thanks for the reply Euro.

m3cliff

Did you have to replace the whole diff? How dud you fix it?

UPDATE: finally changed the bearing, not a job I will do again! Fixed the problem, no more clunk when coasting .