Trying to pinpoint a driveshaft issue

[anthony16r]

Hello everyone,

I've been experiencing a cowbell noise on my 08 m3 like many other owners. It happens when applying load at low speeds typically, or going into reverse. After reading countless threads on the issue, I've decided to inspect the driveshaft in the hopes of getting to the bottom of the issue.

Once the heat shields were off, I first tried to wiggle the driveshaft while still mounted. There was no play at the U-joint, center support bearing, CV joint, or flex disc. But with the handbrake engaged, I was still able to rotate the shaft back and forth with my hand by a few degrees which produces a clunk in the differential, is that normal?

I then took the driveshaft off, and confirmed that there was no play in the U-joint, or CV joint. The center support bearing has very minimal play, which may be responsible for some of the vibrations I've experienced at high speeds, but I've been told it is normal to have a little play.

I'm not positive on the cause of the cowbell noise at this point, but I will be replacing all serviceable parts anyway now that I'm this far in (flex disc, center support bearing, all fasteners, re grease the splines where both half shafts meet). I'm hoping that'll fix it, but I'd like to figure out whether there is also an issue with my differential. I'd also like to know if there is anything else here I should be noticing and am not.

Differential driveshaft flange play:

Same play, with driveshaft still mounted: https://youtu.be/EgkhgXMYDDo

1) Is it normal for the differential flange to rotate by a few degrees while the handbrake is engaged?
2) On a different note, I did not mark the position of one half shaft in relation to the other before disassembly. Any experienced people care to chime in on whether this is actually an issue from first-hand experience? I've heard contradicting opinions and could use some more.

Thanks in advance for any help. I'm happy to provide more info as needed.

-Anthony

[tdott]

The nut holding the two half's together. Likely isn't tight enough.

[anthony16r]

Originally Posted by tdott

The nut holding the two half's together. Likely isn't tight enough.

Thank you for your response. There was no play at the junction between the two halves, and that nut was quite difficult to break loose (the driveshaft is now disassembled), so I doubt that was the problem here.

[tdott]

Originally Posted by anthony16r

Thank you for your response. There was no play at the junction between the two halves, and that nut was quite difficult to break loose (the driveshaft is now disassembled), so I doubt that was the problem here.

Yes there is treadlocker on it from the factory. That doesn't mean it was tight enough. Checking for play with your hand wouldn't apply enough tq to cause it.

I have fixed the noise on several cars where I did nothing but tighten that nut while the ds was still on the car. No more noise after.

[anthony16r]

Originally Posted by tdott

Yes there is treadlocker on it from the factory. That doesn't mean it was tight enough. Checking for play with your hand wouldn't apply enough tq to cause it.

I have fixed the noise on several cars where I did nothing but tighten that nut while the ds was still on the car. No more noise after.

Ok thank you. When putting it back together, should I just go as tight as I can then? I don't know if I'll be able to fit a torque wrench in there. I also may have to go get it balanced if it turns out the alignment of the splines is critical.

[tdott]

Originally Posted by anthony16r

Ok thank you. When putting it back together, should I just go as tight as I can then? I don't know if I'll be able to fit a torque wrench in there. I also may have to go get it balanced if it turns out the alignment of the splines is critical.

Normal practice is to mark it and put it back together in the same spot.

Yea, I don't believe there is a tq spec and there is not enough space to use a torque wrench anyways.

Check newtis, but I don't believe I saw one, also there is some directions you might want to read, such as lining up the ds with the diff input : https://www.newtis.info/tisv2/a/en/e...shaft/1M2eLTGB

[gfxman]

I dealt with this about 2 months ago. It was the center support bearing. I had minimal play, old csb felt and looked to be in great shape. Play was all very minimal to the point where I wasn't sure if replacing the csb actually fixed anything. But when I started driving, cowbell noise was gone, 2 months later I haven't heard that noise ever again no matter how hard I try. Be sure to screw the exhaust clamp parts that connect the mid pipe to the exhaust carefully at the correct angle so the back of the bolts don't touch the heat shield. That created some noise for me that I had to fix later.

**Edit**
Well, now that I read some of the responses, it certainly could have been caused by a loose nut connecting the two halves of the drive shaft, it could have been resolved just by the act of putting it all back together and tightening that driveshaft bolt.


Here is a video I took of the play in the driveshaft, before with old csb and then with new csb.

[da jemster]

Just did the work on my Mechatronics sleeve. I had to unscrew the bolts on my CSB to get slack on the output shaft. It was recommended to replace the CSB bolts. The replacement bolts I received from ECS weren't identical to the ones I had uninstalled. Even though I ordered the correct part number, https://www.ecstuning.com/b-genuine-...t/22326760945/, these new bolts had washers on them. Now my "cowbell" is gone! :-) When reinstalling the CSB, make certain you push them towards the front of the car, like on E46's, you have to pre-load them, then tighten to torque.