On/Off Throttle Clunk Diagnosis

[PSUEng]

Recently I've noticed that in gear, on/off throttle, I get a clunk/thud from the rear end. It's worse in Sport mode, and worse during shifting unless I slip the clutch a little prior to lifting off the throttle. Searched around and I can't make out the "M-clunk" vs. any other problems from the thread results, so apologize in advance if there is a thread already.

My "hunch" is, driveshaft u-joint. The entire driveline is original at 81k--visually, the guibo looks good last time I was under it a few weeks ago fixing the CPV. I'm going to get the rear end up this weekend and attempt to do a few inspections on the driveshaft (excessive play) and attempt to check the axle CVs for play.

What do you guys think? If it's the driveshaft, I like a complete rebuilt solution like the Beyer.

[Cubieman]

I have the same issue,unless I am VERY smooth on/off throttle the car jerks back/forth like when you shift badly.

After a VinceBar, all new rear end bushes (OEM except solid SF), CSB, Guibo, the "clunk" feeling/sound has gotten less but the driveline slack is still felt just as much.

I believe in my case it is passenger side OPF play in the diff., other than that maybe U-Joint or god forbid the tranny has an issue. I may start with a diff. rebuild since I want to go to stock gearing anyways and then install the "free play fix shims" from diffsonline.

[eacmen]

Doubtful its the driveshaft itself. Likely either the center support bearing or front diff bolt.


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[Ramps]

I have the similar clunk when I clutch in ever since I replaced all the rear end bushings (OE) and did solid SF bushings. I think it’s because I didn’t preload the CSB…didn’t know you had to. I am going to preload it at some point and see if that fixes it.

[PSUEng]

Well, I"m trying to bundle work here with the SS exhaust I've got coming, and troubleshoot accordingly. If money were no object, I'd just do all the diff bushings, input seals, etc and just get it over with. What's the consensus on the upgraded diff mount bolts affecting this?

Cubie--when you say OPF--please explain ( I can't think of the acronym at the moment!)

To be fair here--I've driven my '21 STI more lately and maybe I just suck at the M3 driving skill...who knows.

[EthanolTurbo]

M3 is a very clunky car, you can do all of those and improve the feeling but I've begun to believe that a lot of it is in the diff itself. E46 M3 stock rear diffs don't seem to last very long based on what I've read, and as it gets more worn out there's more play generated in the diff itself which you feel through the whole driveline.

Personally, I have replaced the rear diff CV joint, guibo, driveshaft support bearing, all the rear suspension etc and after everything, I'm 99% sure it's the worn out diff that has lasting drivetrain slack and "clunk." I will also work on replacing the axles because might as well when doing the diff.

Hope this saves you some heartache if you decide to replace all of the drivetrain wear parts and still feel it. This is also why I truly feel for someone's wallet when their M3 has 80k+ miles and all of this stuff is worn out and it's time to replace everything. It's not cheap or easy if you want to refresh everything let alone upgrade stuff.

I've also begun to believe it's an E46 M3 thing specifically, because the E39 M5 doesn't really suffer from this. The shifting action and driveline play for the E39 is much more precise and eloquent on similar mileage cars.

Also, one little tip that helps a lot is not driving in sport mode. Regular throttle has a lot more linear action so it's much easier to keep the clunking to a minimum, whereas the sport throttle isn't nearly as smooth when modulating.

[Gearhead55]

+1 for not driving in sport mode. I don't even use that on the track.

[Cubieman]

Cubie--when you say OPF--please explain ( I can't think of the acronym at the moment!)

Diff. Output Flange, next time yours is up in the air (or at least the rear wheels) try very slowly rotating your wheels by hand and watch when your driveshaft starts to move.

In my case I can rotate the driver's side wheel and I see the driveshaft rotate immediately and when I rotate the passenger side wheel there is a bit of slack or take-up before the driveshaft starts to spin.

I can also move my passenger side diff. OPF up/down a bit as well whereas the driver's side will not move like that.

I think what I am seeing is somewhat normal for a "V1" diff. and on a "V2" diff. it is the driver's side that has the slack. The V1 vs V2 is model year dependant I don't remember which is which.
My diff. was rebuilt/installed with 4.10's in 2015, I bought the car in early 2018 fwiw and I feel its got an issue.

I feel that surge on/off gas even with 100% new rear end bushings (all of them), this is why I believe in my case it's something else, the diff. bushings are talked about a lot and yes that does help and/or fix some clunk issues but the diff. on these vehicles doesn't seem to be the greatest unfortunately, combine that with multiple owners and 100k+ cars, it may soon be time for that unfortunate expense of a refurbished diff.

I am going to either just buy an a pre-assembled OS Giken/Wavetrac or more likely (because money) source a used stock diff. and attempt a full rebuild.

Here is a video I made a while ago, it shows the up down movement kind of, the rotational movement looks more like a driveshaft C.V issue.

https://youtube.com/shorts/8ZmcfuX2wF0?feature=share

[Thrifty S50]

Yup its diff related. It is common (unfortunately) to have free play in the passenger side stub shaft, racing diffs sells a shim kit to resolve this i believe

[sapote]

or god forbid the tranny has an issue..

Sleep tight; tranny issue will not cause this clunk thing, but it will scream.

[sapote]

I have the similar clunk when I clutch in ever since I replaced all the rear end bushings (OE) and did solid SF bushings. I think it’s because I didn’t preload the CSB…didn’t know you had to. I am going to preload it at some point and see if that fixes it.

Preload CSB or not doesn't cause the clunk. It affects the bearing noise or its life span.

[sapote]

In my case I can rotate the driver's side wheel and I see the driveshaft rotate immediately and when I rotate the passenger side wheel there is a bit of slack or take-up before the driveshaft starts to spin.

V1 diff: the left out put flange OPF splines are driving the clutch pack directly and the clutch drives the ring gear directly, so no play. The right OPF splines drive the ring gear through the side-gear and spiders, and there is plays between side-gear and spiders.

[sapote]

What do you guys think? If it's the driveshaft, I like a complete rebuilt solution like the Beyer.

More likely I think the old LSD clutch pack slips then the side-gear hammers the spiders. To fix: new clutch pack and reduce the plays at the side-gears.

[Tones]

My car has the same. Jack up your rear and move the wheel back and forth by hand. When i did this the clunk was from the diff and it's loud. The clutch packs in the lsd wear out around 80-100k. Mine started around 120k after lots of mtn runs

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[PSUEng]

I got both rear wheels up in the air and in neutral/e-brake off, there is noticeable play when rotating each wheel. More of a thud on the driver side and clicking on passenger side--but play on both sides. Mine is a 12/02 build, 81.3k miles. So then, clutch packs wearing? How long can I drive like this and what else will wear out until I fix it?