Clunk noise! Need help..

[DRLane]

Originally Posted by pbonsalb

Maybe the flex in them contributed to the problem. I would have done hard subframe mounts like 75D poly or Delrin or aluminum and not quite as hard diff mounts. I use 75D subframe and 95A diff, for example.

The subframes mounts should be at least as hard as the differential mounts. I would think that's what put the added stress on the diff.

The subframe upgrade and suspension are what improve the wheel hop. Not sure how the diff mounts would improve that. If anything that protect the diff from moving when the subframe is more rigged.

[JetBlack_M3]

Originally Posted by DRLane

The subframes mounts should be at least as hard as the differential mounts. I would think that's what put the added stress on the diff.

The subframe upgrade and suspension are what improve the wheel hop. Not sure how the diff mounts would improve that. If anything that protect the diff from moving when the subframe is more rigged.

I'm gonna do the MRF engineering subframe mounts, for the differential mounts should I stick with the solid delrin mounts from Turner or do purple poly mounts?

[pbonsalb]

For your purposes try keeping the solid diff mounts. If you can’t take the whine try 95A. I would go softer to purple 80A only if the 95A are too much for you.

[GotV8?]

I went with Turner Aluminums sub frame mounts paired with the purple flex differential mounts: The whine is minimal; imo: I also run 295 tires and No wheel hop and no issues. It may be possible that when you left your sub frame OEM setup and only upgrade your diff mounts that you caused more stress on differential even though you got rid of the wheel hop.

[JetBlack_M3]

Originally Posted by pbonsalb

For your purposes try keeping the solid diff mounts. If you can’t take the whine try 95A. I would go softer to purple 80A only if the 95A are too much for you.

Tbh I don't mind the diff. whine. I just figured going with purple mounts are less harsh than the solid mounts

[JetBlack_M3]

Originally Posted by GotV8?

I went with Turner Aluminums sub frame mounts paired with the purple flex differential mounts: The whine is minimal; imo: I also run 295 tires and No wheel hop and no issues. It may be possible that when you left your sub frame OEM setup and only upgrade your diff mounts that you caused more stress on differential even though you got rid of the wheel hop.

Maybe so, few people mentioned that as well. I'm gonna go ahead and change the subframe mounts since were already dropping the diff

[pbonsalb]

Originally Posted by boussi33

Tbh I don't mind the diff. whine. I just figured going with purple mounts are less harsh than the solid mounts

I don’t think the solid mounts have anything to do with your diff problem. Plenty of people run solid on street cars and race cars with no issues. I think you problem was too much hop. Unless maybe it’s the fluid like someone else suggested. If you run fluid without friction modifier your diff will make sounds that will worry you. You have not written anything about fluid changes so I assume that is not the issue.

[JetBlack_M3]

Originally Posted by pbonsalb

I don’t think the solid mounts have anything to do with your diff problem. Plenty of people run solid on street cars and race cars with no issues. I think you problem was too much hop. Unless maybe it’s the fluid like someone else suggested. If you run fluid without friction modifier your diff will make sounds that will worry you. You have not written anything about fluid changes so I assume that is not the issue.

I'm running the bmw diff. Fluid. It has the friction modifier in it. It surprises me that no one has ran into an issue with their differential after running solid mounts except for myself hahaa. Hopefully the new diff and solid subframe will solve it

[bvrider1]

When do you plan on installing the new diff?

Originally Posted by boussi33

I'm running the bmw diff. Fluid. It has the friction modifier in it. It surprises me that no one has ran into an issue with their differential after running solid mounts except for myself hahaa. Hopefully the new diff and solid subframe will solve it

[JetBlack_M3]

Originally Posted by bvrider1

When do you plan on installing the new diff?

Hopefully later this week, early next week. The diff I got has 55k miles on it. Just opened it up today and looks good

[DRLane]

Originally Posted by pbonsalb

I don't think the solid mounts have anything to do with your diff problem. Plenty of people run solid on street cars and race cars with no issues. I think you problem was too much hop. Unless maybe it's the fluid like someone else suggested. If you run fluid without friction modifier your diff will make sounds that will worry you. You have not written anything about fluid changes so I assume that is not the issue.

I doubt there are folks that have upgraded their diff mounts to solid and leave subframe rubber. It's generally the otherway around, where folks run solid sub and leave the diff stock due to whine.

Here's a snippet from AKG Motorsports regarding subframe. Also, I believe MRF has said the same.

Maybe call a race shop and ask their opinion.

[DRLane]

boussi33

This is a great thread to read! Makek would be a great resource to call.

https://www.m3post.com/forums/showthread.php?t=926758

[JetBlack_M3]

I appreciate all the help I received in this thread. I'm gonna go ahead and install the MRF subframe mounts, get the old differential opened up and report back to you guys!

[JetBlack_M3]

Originally Posted by DRLane

boussi33

This is a great thread to read! Makek would be a great resource to call.

https://www.m3post.com/forums/showthread.php?t=926758

Thank you, the threads you provided were certainly helpful

[Bubbles]

Originally Posted by boussi33

Thank you for the advice! We took down the driveshaft to see if the issue was from the differential or driveshaft and the diff continued to clunk as we rotated the wheels. I can assume at this point my diff is out. I got another diff with low miles. Hopefully it solves the issue

I had a similar sound replaced the rear cvjoint with redline cv2 grease. Also switched to the shell version of the diff fluid. Most if the sound is gone.

[JetBlack_M3]

Originally Posted by Bubbles

I had a similar sound replaced the rear cvjoint with redline cv2 grease. Also switched to the shell version of the diff fluid. Most if the sound is gone.

But did you get the clunk sound whenever you accelerate?

[Bubbles]

Originally Posted by boussi33

But did you get the clunk sound whenever you accelerate?

Somewhat of a clunk, my cv joint was sticking and I could see uneven wear on the bearings when I took apart the cv joint.

[JetBlack_M3]

Originally Posted by Bubbles

Somewhat of a clunk, my cv joint was sticking and I could see uneven wear on the bearings when I took apart the cv joint.

I'm probably gonna drop a carbon fiber driveshaft and get rid of the shitty 2 piece shaft

[jiggysnitz]

Really interested if you find a solution here. I have had a similar clunk since I bought my car a year ago. It already had solid diff and subframe mounts when I bought it. Here is the list of just about everything I could think to replace while trying to get this quieted down the back end:

New/rebuilt driveshaft
CSB
Guibo
New diff (was junk)
Another new diff
Rear shock upper mounts
Trans mounts

Not sure where to go next on this. Maybe I got a third diff with the exact same issue but that seems unlikely.

[JetBlack_M3]

Originally Posted by jiggysnitz

Really interested if you find a solution here. I have had a similar clunk since I bought my car a year ago. It already had solid diff and subframe mounts when I bought it. Here is the list of just about everything I could think to replace while trying to get this quieted down the back end:

New/rebuilt driveshaft
CSB
Guibo
New diff (was junk)
Another new diff
Rear shock upper mounts
Trans mounts

Not sure where to go next on this. Maybe I got a third diff with the exact same issue but that seems unlikely.

Gonna send you a PM

[jiggysnitz]

Did you ever find a solution? My similar clunk is attacking my OCD and ruining the car for me 😑

[G60nut]

I'm also interested in in the out come. I noticed the same Aluminum bat noise when the drive train is loaded and unloaded during normal driving. I can also replicate the noise in the drive way at idle by holding the brakes and just slightly letting the clutch out in 1st then Reverse.