M4 Differential clunk once

[andrei.m4]

10k km ago my diff started to knock when i put car in reverse and accelerate, now if i let car to lower speed from 3th gear to 2th, when it put it in 2th gear rear diff knock once, and when i press again acceleration differential knock again once, but only one time. Anyone with this problem? Only one knock and then I can accelerate without problems or others strange sounds... i lifted up the car and sound is inside rear diff, all bolts are torqued corectly.

[G4BR13L]

M4 from 2016 or earlier? How many kilometers do you have now?

[andrei.m4]

M4 2015, 100k km, oil in differential is new. Msp/a 75w140

[G4BR13L]

Originally Posted by andrei.m4

M4 2015, 100k km, oil in differential is new. Msp/a 75w140

If it started 10000 km ago I guess that we can rule out causes by wrong fluids used. If this was under warranty they would replace the diff and the mounting bolts.

Can you post a video where we can hear it?

[andrei.m4]

I will make a video tomorrow, no warranty to car sound was same before oil change/after oil change, the old one was clear, without metalic parts inside or something, i replaced it with msp/a oem 75w140 same sound then i replaced with motul 75w140 gear competition limited slip and the sound is same. Tomorrow I will try to put phone unde car to make a video.

[G4BR13L]

Fluid viscosity is good, I believe that BMW uses Castrol SAF-XJ. If it was a bearing there would be a constant noise. Imho it is just wear and the rear diff needs to be replaced or revised.

My guess is too much backlash between the gears which can be resolved with shims but the best way to check is to open it up.

I am afraid that BMW does not sell replacement parts for the rear diff. New one will cost about 3000 euro not counting the labour and let’s say that a revision will cost you around 1000 euro. You could also buy a used one (from a salvage car) and just put new seals.

[mfurse]

Does the noise sound like this?

[Kisenwether]

Im currently 4 months into battle rear diff clunk and also grinding when turning. Had a bmw engineer out last week who said it was normal. I couldnt reproduce the grinding at the time but just figured it out tonight how to do it on demand. They have another engineer coming out next week.

I have a clunk when getting on the throttle and off.

Car is a 2015 M3 with 40k miles DCT.

[G4BR13L]

Originally Posted by Kisenwether

Im currently 4 months into battle rear diff clunk and also grinding when turning. Had a bmw engineer out last week who said it was normal. I couldnt reproduce the grinding at the time but just figured it out tonight how to do it on demand. They have another engineer coming out next week.

I have a clunk when getting on the throttle and off.

Car is a 2015 M3 with 40k miles DCT.

The differential has a multi disc clutch so when you hear it in corners it could be that sometimes the friction plates hit the clutch discs.

[andrei.m4]

My m4 never clunk when turn or something else, as I said only when I put a bit tension in oposite way on transmision, if I try to go reversing easy, with a little little acceleration just enough for dct to go reverse clunk not come, but when i press a little more diff clunk. My output shafts was replaced cause the mecanic said first time the clunk is from them, but clunk not resolved.
Edit: I talked with someone and he told me to check the big nut in front of the differential, where diff connect with carbon propshaft, it need to be torqued at 120nm, for this the carbon propshaft need to be unmounted, then remount all.
And the video:

My brake is pressed to make the moovie but in normal run i don t need brake, clunk noise hear with brake or without, as I said a little transmision on oposite way make this noise.

[petrolhead.]

Originally Posted by andrei.m4

10k km ago my diff started to knock when i put car in reverse and accelerate, now if i let car to lower speed from 3th gear to 2th, when it put it in 2th gear rear diff knock once, and when i press again acceleration differential knock again once, but only one time. Anyone with this problem? Only one knock and then I can accelerate without problems or others strange sounds... i lifted up the car and sound is inside rear diff, all bolts are torqued corectly.

I had EXACTLY the same symptoms. Took it to the shop and they re-glued the carbon drive shaft to the bolt that connects to the diff. That was done about 3000km ago on my car (16000km in total). The problem has not come back so far.

[G4BR13L]

Originally Posted by petrolhead.

I had EXACTLY the same symptoms. Took it to the shop and they re-glued the carbon drive shaft to the bolt that connects to the diff. That was done about 3000km ago on my car (16000km in total). The problem has not come back so far.

They glued what exactly?? Are you talking about the flange?

[Kisenwether]

I think he is talking about a bolt between the drive shaft and rear diff and not glue but loctite. That's one of the attempts they made on my car and made no difference.

[G4BR13L]

Originally Posted by Kisenwether

I think he is talking about a bolt between the drive shaft and rear diff and not glue but loctite. That's one of the attempts they made on my car and made no difference.

I did not know that a threadlocker is needed for the driveshaft bolt. I thought that these were just tightened at correct torque (120Nm). I looked up the procedure and you are right as Loctite 648 is used. The procedure is not complex but fragile.

[G4BR13L]

Originally Posted by andrei.m4

My m4 never clunk when turn or something else, as I said only when I put a bit tension in oposite way on transmision, if I try to go reversing easy, with a little little acceleration just enough for dct to go reverse clunk not come, but when i press a little more diff clunk. My output shafts was replaced cause the mecanic said first time the clunk is from them, but clunk not resolved.
Edit: I talked with someone and he told me to check the big nut in front of the differential, where diff connect with carbon propshaft, it need to be torqued at 120nm, for this the carbon propshaft need to be unmounted, then remount all.
And the video:

My brake is pressed to make the moovie but in normal run i don t need brake, clunk noise hear with brake or without, as I said a little transmision on oposite way make this noise.

If you want to give the procedure a shot follow this:
Removing and installing carbon propeller shaft (inserted) complete S55

[Oscmejia81]

I had a 2015 BMW M4 before that made a grinding noise and it was the drive line coming in contact with with the shield, it always happened at low speeds!