Thud/clunk from drivline-rear end

Hey all,

I’ve been recently troubleshooting a thud coming from my driveline/rear end, when I first purchased the car I double checked the vehicle for subframe cracks even though PO had recent inspection by dealership, couldn’t identify any via visual inspection so decided to tackle the differential bushings. I replaced all 3, job only slightly annoying, correct tools and watching youtube DIY videos are a must. Anyway put the car back together and still have the mysterious thud sound. It happens exclusively when disengaging the clutch when changing gear. Its not completely constant, usually more prevalent at lower RPMs.
I’ve done a bunch of reading on some of the culprits, and am going to check the subframe mounting points again tomorrow but if I still cant see any cracks would a thud sound be possible if no visible cracks (aware there could be small ones I cant see unless I drop rear end). Read about CSB and Guibo on the driveshaft but that seems to be more of vibration/whining issue no? When I was doing the bushing job examined the rear sway bar end links and bushings and seemed fine as well, but could these come into play? Any chance the differential could have some type of wear on its splines that would cause this sound?
Also will mention engine and transmission mounts have been replaced by me and I believe the clutch+flywheel(130k) are original.

Thanks ahead time and sorry for the word vomit just wanted to try add as much context as possible.

Have you looked at the rear shock mounts? That would also create the same sound you're describing as well.

have not, know the shocks/stuts have been replaced, ~40k on them right now. I’ll add it to my list of things to check tomorrow.

I have the exact same clunk. I have new diff bushings and all new suspension. The only thing I haven't done yet are subframe bushings. Those are the most likely culprit, as old bushings will allow the entire subframe to move around drastically when drivetrain loads change (like letting go of the clutch) and hit other parts of the car as seen here:

https://www.youtube.com/watch?v=6ukbQHA4SnA

rear subframe bushings I would suspect, if not, check the drivetrain/guibo/etc.

Could it also be the driveshaft guibo/flexdisc (26117511454) or the center support bearing (26127501257)?

I just checked shock mounts does appear like they are ready to be replaced. Its possible it could be either flex disc or center support bearing but I also don't really experience any prolonged vibration after initial thud. As it relates to subframe bushings if one is bad, am I’m potentially damaging mounting points driving the car?

I wouldn't be driving around beating on the car. normal cruising would be fine I would assume, but the sooner you replace them the better. if you are going to do all the subframe bushings, might as well do RSMs and other associated rear bushings/mounts. kind of a "while you are in there" type of thing.

Also how do you guys post pictures on here, doesn’t let me attach photos from my phone, even when I changed the format. I’m going to change RSM first, the metal appears to have separated from the rubber. I was planning on replacing subframe bushings+ reinforcing at some point, and while I feel comfortable dropping the rear end dont have any welding experience and would feel like a waste not installing some reinforcement plates, especially since they aren’t all that expensive, has anyone went with the epoxy method?

if you plan on keeping the car for a while, this is just my opinion, but don't cut the corners. find a shop that can do the reinforcement welding for you.

"set it and forget it"

whats a reasonable price in y’alls opinion for the job? And does anyone have any recommendations for shops in philly area?

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Originally Posted by zhaireszhp

Also how do you guys post pictures on here, doesn’t let me attach photos from my phone, even when I changed the format. I’m going to change RSM first, the metal appears to have separated from the rubber. I was planning on replacing subframe bushings+ reinforcing at some point, and while I feel comfortable dropping the rear end dont have any welding experience and would feel like a waste not installing some reinforcement plates, especially since they aren’t all that expensive, has anyone went with the epoxy method?

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if there are cracks, you're going to have to weld before you epoxy. Just call a mobile welder to come to you if you're trying to save some money. Otherwise, go to a shop.

yeah, still can’t visibly inspect any cracks, was the same when I had the diff dropped, possible some hairline cracks exist when the subframe is dropped though. Regardless of what I do probably not going to drive it for awhile if RSM don’t do anything.

Prices for RACP reinforcement can vary greatly... the number of cracks to fix, whether the left rear seam in the wheel well has split and needs welding, are you going to replace your bushings or not (and which bushings?) all influence the cost. Best thing is to call a few reputable shops and ask for quotes.

Mine was ~$1800-1900 CAD to fix all the cracks, weld the split left rear seam in the wheel well, weld Redish reinforcement plates, paint/undercoat the affected areas. Then install powerflex subframe bushings & RTABs, and OE diff bushings. Keep in mind this was 5 years ago, that shop had a great deal and prices have likely gone up since.

Yeah I have seen prices anywhere from 1500-3000 browsing e46fanatics. Would have to call around, mobile welder would be interesting to me, would be nice to examine the welds and generally speaking like working on the car and learning how everything fits together. But if I do go professional shop would have let the car sit as classes are starting up soon and don’t think I could swing the price tag w/o saving up some more. Also whats the recommended brand for rear shock mounts, I saw meyle, lemforder and sachs on FCP Euro.

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Originally Posted by zhaireszhp

Yeah I have seen prices anywhere from 1500-3000 browsing e46fanatics. Would have to call around, mobile welder would be interesting to me, would be nice to examine the welds and generally speaking like working on the car and learning how everything fits together. But if I do go professional shop would have let the car sit as classes are starting up soon and don’t think I could swing the price tag w/o saving up some more. Also whats the recommended brand for rear shock mounts, I saw meyle, lemforder and sachs on FCP Euro.

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Get Lemförder for shock mounts. You can also look at some aftermarket options that might last longer. I have these for example: https://www.bimmerworld.com/Lifetime...unt-Set_2.html

It's definitely worth saving up for the rear end reinforcement.

yeah it was my plan to get it done anyway, just was hoping i could enjoy the car for a little while before i splurge on the job. But if the noise persists even after i change the rear shock mounts not going to feel super comfortable driving it around, don’t think I have cracks right now or if i do they must be quite small, but still don’t want to chance it.

Also how long have you had those shock mounts and what kind of suspension are you running? I read some comments about meyle hd ones on fcp euro and one person mentioned they might not fit well w/ certain bilstein setups.

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Originally Posted by zhaireszhp

Also how long have you had those shock mounts and what kind of suspension are you running? I read some comments about meyle hd ones on fcp euro and one person mentioned they might not fit well w/ certain bilstein setups.

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I'm running the performance option from my guide: http://www.zhpmafia.com/forums/showt...M-SACHS-Setup)

Can't go wrong with Lemförder, all their parts are excellent. Meyle HD can be hit or miss.

Gotcha thanks, and yeah my experiences with lemforder have been very good, whether on this car or a e39 530i i used to have.

I like the rogue RSMs. one of the few things I like from them. Reinforces that area. Plus it helps when after you install that, you don't ever gotta take out the trunk to replace the shocks since the nuts are now under the wheel well.

https://www.bimmerworld.com/Suspensi...0-E36-E46.html

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Originally Posted by zhaireszhp

yeah, still can’t visibly inspect any cracks, was the same when I had the diff dropped, possible some hairline cracks exist when the subframe is dropped though. Regardless of what I do probably not going to drive it for awhile if RSM don’t do anything.

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Yeah a lot of times when you're inspecting, it requires you to remove the protective undercoating first in the common trouble areas. Then only after that will you see the cracks.

I ran Meyle HD RSMs with Bilstein B4s without issue, but only for about 20k kms. For a street car I'd probably go with Lemforder, paired with reinforcement plates.

Here's a pic of the 1 large crack I had, before undercoating was cleaned off. Quite faint but it's there. Most smaller cracks will be very hard to see, either due to undercoating or just blocked by the bushings:

https://i.imgur.com/wZhUJf7l.png

yeah its possible i smaller cracks i cant see due to undercoating/subframe, not sure theyd warrant the thud noise though. for those who have had their subframe mounts reinforced by a shop, did they repaint your subframe?

Tangentially related, i was planning this job for when i decided on what lsd i wanted to install, seems like torsen style would be right for me but am curious about install, do most just go the pumpkin route or find a shop that can install it into factory diff?

Repainted the subframe itself, no mine's still really crusty. Honestly I'll probably just let it crack, and then repaint the replacement lol.

If I were to get an LSD installed I'd order the core itself, then have a transmission shop replace it. I normally like to DIY a lot of things but I don't have the tools (nice vise on a solid bench) nor the time, and I wouldn't want to screw something up.

Quote:

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Originally Posted by zhaireszhp

Tangentially related, i was planning this job for when i decided on what lsd i wanted to install, seems like torsen style would be right for me but am curious about install, do most just go the pumpkin route or find a shop that can install it into factory diff?

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I think it depends on your budget and stuff. Normally I would just get the LSD itself and swap into my pumpkin too since DIY. But I'm lazy nowadays, so I'll just swap the whole pumpkin. Maybe sell my old one to recoup or something.

I have the tools for the DIY, those snap-ring shims look like a pain though. when i had the diff out i had a brief moment where i was going to say fuck it and just order one to have installed but better judgement got the best of me haha.

Got some quotes the last couple days, found a competitive one and seems like the shop is run by good people, ~2100-2200 for reinforcement+ all bushings replaced. Haven’t officially confirmed w/ them yet but how accommodating they’ve been w/ all my questions/concerns has really stood out. Probably called a dozen and a half shops and it kind of surprised me that that wasn't always the case, especially since this is kind of a big job.

did you ever replace the RSMs to see if the clunk goes away since that's easy to replace and probably cheaper than the subframe stuff.

Really late on this response but maybe it'll be useful for someone in the future, I did change my RSM but noise was still present so I got my subframe reinforced by a shop in like late October. Sadly noise was still present after that job as well. What it ended up being was the CSB was toast. Kind of annoying the shop wasn't able to diagnose, they had my car for like a month and half and insisted it wasn't subframe cracking and just thought it was due revshift bushings I had installed. My guess is they never really checked the driveshaft as much of it covered by a heatshield. Final cost was like 2600 bucks for reinforcement + subframe and differential bushings (had them revert back to OEM just in case that was a factor).