Clunking when on/off the gas quickly

[bimmer]

The diff has excessive play (can see this in my video from above posts) and is creating a lot of driveline backlash. Seems U-Joint on the driveshaft is starting to go. I almost replaced it last time I had it out but told myself I'd wait. Vibrations have gotten worse since then, perhaps from the backlash? Grabbing a rebuilt one from driveshaft specialists for just under $500.

I'm also considering moving to a 3 clutch setup. Given budget, I need to choose between that or the 4.1 gearing and am torn. Wondering which I will notice/value more. My local tracks are Lime Rock and Thompson. I suppose I value a more stable car than one that accelerates slightly faster, and the 3 clutch should last longer than the M-variable. I just chatted with Dan (very nice and helpful guy) on the phone and essentially we landed with me needing to make a decision on that trade off given my budget. Hmmm....

[Mattn1192]

What did you end up doing to fix this issue with the excessive play/slop?

[cudzich09]

Had a similar issue. On off throttle produced a clunk, entire speed range. CSB was replaced, nor was it damaged, and it did not fix the issue. Swapped in 65k mile diff, problem gone.

If you're swapping in a lower mileage diff, at the very least, replace the output shaft seals and fluid.

[bimmer]

What did you end up doing to fix this issue with the excessive play/slop?

Ended up replacing the diff with a rebuilt unit from diffsonline which resolved the issue.

[Toby22]

Indy confirmed today that the differential is very much shot and driveshaft should probably be replaced. Not surprising at 150K.

What did they do to confirm this? 150k miles doesn’t seem much to replace diff. Curious if mine is shot since I have the clunk and replaced everything (including driveshaft) minus the diff.

[bimmer]

What did they do to confirm this? 150k miles doesn’t seem much to replace diff. Curious if mine is shot since I have the clunk and replaced everything (including driveshaft) minus the diff.

To be honest I didn't really ask them much about how they tested it. They told me there was excessive play in the diff causing driveline backlash and it's an indie I trust so I left it at that. I posted a video earlier in this thread and I'm pretty sure that's what I was seeing. The rebuilt diff fixed the issue so I never really thought about it again. From what I remember researching at the time 125K-150K is pretty common for the factory diff to call it quits.

[CrisSilberGrau]

To be honest I didn't really ask them much about how they tested it. They told me there was excessive play in the diff causing driveline backlash and it's an indie I trust so I left it at that. I posted a video earlier in this thread and I'm pretty sure that's what I was seeing. The rebuilt diff fixed the issue so I never really thought about it again. From what I remember researching at the time 125K-150K is pretty common for the factory diff to call it quits.

Did you opt for different gearing? What was the rebuilt one specc'd like, also cost if you dont mind. Gald its gone, I feel mine is on the way out, I get lugging in gear if im not super careful taking off and at the track it feels lazy to lock up, but im a noob in that department so far.

[bimmer]

Did you opt for different gearing? What was the rebuilt one specc'd like, also cost if you dont mind. Gald its gone, I feel mine is on the way out, I get lugging in gear if im not super careful taking off and at the track it feels lazy to lock up, but im a noob in that department so far.

I ended up just getting a rebuilt stock M-variable unit from Diffsonline. As much as I wanted to change gearing or go to a 3-clutch it just wasn't in the budget at the time. It ended up being ~$1450. There is a $1500 core deposit and I was already heading up to Boston area so I just dropped the core off. I imagine shipping something that big and heavy is probably a couple hundred bucks? I also replaced mine myself so not sure how much it would cost to have a shop do it if you are going that route.

I will say I noticed a big difference on corner exits at the track vs. the old tired diff.

[CrisSilberGrau]

I ended up just getting a rebuilt stock M-variable unit from Diffsonline. As much as I wanted to change gearing or go to a 3-clutch it just wasn't in the budget at the time. It ended up being ~$1450. There is a $1500 core deposit and I was already heading up to Boston area so I just dropped the core off. I imagine shipping something that big and heavy is probably a couple hundred bucks? I also replaced mine myself so not sure how much it would cost to have a shop do it if you are going that route.

I will say I noticed a big difference on corner exits at the track vs. the old tired diff.

Figures, any other daily things you noticed?

[bimmer]

Figures, any other daily things you noticed?

The diff is a nice painted black instead of a rusty mess whenever I work underneath the car now 😂. But no not really, it's just nice having the clunk gone. Don't really notice the new diff unless on track or doing very spirited street driving.

[sapote]

I posted a video earlier in this thread and I'm pretty sure that's what I was seeing. .

I only saw the video filming the shifter with the clunk noise as you inc and dec the gas pedal. No video of the diff plays, or somehow I couldn't find it.

[sapote]

What did they do to confirm this? 150k miles doesn’t seem much to replace diff. Curious if mine is shot since I have the clunk and replaced everything (including driveshaft) minus the diff.

The clutch stack worn so bad that it slip easily, causing the two side-gears clash to the 4 spider gears and hence the clunk noise. Not the ring/pinion clearance that cause the clunk.

[bimmer]

I only saw the video filming the shifter with the clunk noise as you inc and dec the gas pedal. No video of the diff plays, or somehow I couldn't find it.

Video is linked in the second post: https://youtu.be/9WhbQHotT-U

Next time I'm under the car I'll check to see if there is still that much play. It could be normal and unrelated....I was just hypothesizing at the time

[sapote]

Video is linked in the second post: https://youtu.be/9WhbQHotT-U

That was the drive shaft with pinion/ring plays included, and so it is hard to make the conclusion. It is best to jack one wheel up and try to check the plays when rock it back/forth but don't turn too far that it rotates the drive shaft. This is the diff side-gear to spider gears plays which caused the cluck.

[Ubaderb]

If you roll your car back slowly while in neutral and you pull the ebrake to stop, does the rear end lift? I encountered what you felt and swapped a lower mile diff and problem gone. Definitely too much slop in the diff. Otherwise, it can also be the driveshaft or CV.

I realize that I am bumping an older thread but is this a good way to check? I say this because I have an ever so slight incline on my driveway that when I park the car rolls back and feels like the rear end lifts. I always thought this was just my parking brake needing adjustments or something.