Subframe Bushing - Source of Clunk Noise

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Sbeaud
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Subframe Bushing - Source of Clunk Noise

Post by Sbeaud »

I recently did some suspension work on my 88 M6. Rear suspension work consisted of new self leveling shocks and stab bar links. Now I seem to have a clunk when driving over very small bumps. It is coming from the rear of the car, but it is difficult to tell if it is left or right. Had someone ride in the rear seat, but it could not be isolated/determined. Also, when the car is at rest I lifted the car by hand - lifting by the wheel arch. I can get a couple inches of travel and while doing so had someone (including me) listen/look from under the car. Still can't isolate it, but it certainly is coming from the rear. But I did notice that the while lifting there was movement on the subframe. There was at least 1/4-in of movement between the "push rod" (33311123982) and the subframe. I assume ~2-in of suspension movement should not deflect the bushing that much, correct?
220603 BMW M6 Left Rear Subframe Mount.jpg
220603 BMW M6 Left Rear Subframe Mount.jpg (127.61 KiB) Viewed 2367 times
Thanks

Scott
1988 M6
wattsmonkey
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Re: Subframe Bushing - Source of Clunk Noise

Post by wattsmonkey »

I'm not sure if I'm seeing what I think I'm seeing, but your subframe mounting bushes are a likely candidate.

You'd normally notice them being worn out because the handling gets absolutely terrifying though!!!!!!
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Re: Subframe Bushing - Source of Clunk Noise

Post by Ralph in Socal »

Clunk noise is usually diff mount.

The subframe bushings take a lot of abuse as they hold up a lot of weight. The deflection changes as weight is transferred during normal suspension travel. Look for cracking in the rubber or separation from the metal parts.

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Last edited by Ralph in Socal on Tue Jun 07, 2022 2:43 am, edited 1 time in total.
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Re: Subframe Bushing - Source of Clunk Noise

Post by Slownrusty »

Scott - Those rear subframe bushings seldom go bad, every set I've replaced have been in surprisingly good shape. I have a friend in the Austin, TX who restores BMWs for a living, and he also has observed the same thing....they last for a very long time. I think its due to their stout design and also how they are loaded.

I agree with Ralph, I would check the diff mount.

If you do want to change the rear subframe bushings, you've probably seen my YouTube video on the steps AND I have a brand new OEM BMW set that I'm happy to sell.

My best,
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Re: Subframe Bushing - Source of Clunk Noise

Post by wattsmonkey »

Slownrusty wrote: Mon Jun 06, 2022 7:05 pm Scott - Those rear subframe bushings seldom go bad, every set I've replaced have been in surprisingly good shape. I have a friend in the Austin, TX who restores BMWs for a living, and he also has observed the same thing....they last for a very long time. I think its due to their stout design and also how they are loaded.
That's a new one on me - they are on the things to replace as a matter of course list over here - every E24 or E28 I've owned has needed them. Perhaps it's the state of UK roads.

Diff mount a likely one, as you say. I seem to remember an easy check is to see if there is a clunk when you set off in reverse.

Here's to no more clunking in any case.

Cheers,

Rob
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Re: Subframe Bushing - Source of Clunk Noise

Post by Slownrusty »

Its seems like the Series 2 subframe bushings are an improvement in design over Series 1, even though its more work to replace the Series 2.
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Sbeaud
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Re: Subframe Bushing - Source of Clunk Noise

Post by Sbeaud »

Thanks so much for the input. Been working on other projects...

Diff mount: Not sure of the age, but does not seem to appear bad.
210918 BMW M6 Differential Mount.jpg
210918 BMW M6 Differential Mount.jpg (433.39 KiB) Viewed 2264 times
So given that, and some pics I have from the last few years I think I'll focus on the subframe bushings. My pics show quite a bit of deflection - I don't think that's normal.

Car on jackstand located at the jacking point.
BMW M6 Right Rear Subframe Mount - jackstand on body.jpg
BMW M6 Right Rear Subframe Mount - jackstand on body.jpg (164.07 KiB) Viewed 2264 times
Car on jackstand located on the lower control arm.
BMW M6 Right Rear Subframe Mount - jackstand on control arm.jpg
BMW M6 Right Rear Subframe Mount - jackstand on control arm.jpg (90.21 KiB) Viewed 2264 times
I watched your video Yasin - thanks very much for posting. I would prefer not to remove the subframe to replace the bushings though.

Any thoughts on this tool from ebay?
https://www.ebay.com/itm/334220664913?_ ... %7Ciid%3A1
BMW E24 Subframe Bushing Removal Tool - ebay.jpg
BMW E24 Subframe Bushing Removal Tool - ebay.jpg (86.6 KiB) Viewed 2264 times
A fair amount of info regarding replacing these bushings including this from the My28 forum.
https://www.mye28.com/tech/rods_pages/c ... index.html

Scott
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Re: Subframe Bushing - Source of Clunk Noise

Post by Slownrusty »

Scott - Give that tool a shot, I heard good things as well.

It might be worth buying it for the future.

I had a tough time with the subframe bushings, but will take that any day over the damn Rear Trailing Arm Bushings.

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Re: Subframe Bushing - Source of Clunk Noise

Post by wattsmonkey »

Damn! I paid £250 for a similar tool.

Good luck with this, if your bushes are at all worn you may well be in for a treat with the improved handling with new ones.
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Sbeaud
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Re: Subframe Bushing - Source of Clunk Noise

Post by Sbeaud »

Well, I have not done the subframe bushings yet, but I did fix the clunk noise. Turns out it was probably the most obvious thing. I was pretty sure the sound was coming from the rear of the car, hence the subframe bushing suspicion, but it ended up being the front. The noise was getting worse and finally got to the point I could create the noise by lifting the rear of the car by hand (lifting the wheel arch). Had my wife do so while I was underneath the car and I watched the front stab bar strut move and clunk. Easy fix! I'm pretty sure I torqued these during assembly, but it may have been to a lower value. Which brings up a question about the torque specs. This is what I have for torque specs:
BMW Stab Bar Torque Specs.jpg
BMW Stab Bar Torque Specs.jpg (88.3 KiB) Viewed 1940 times
I may have initially torqued the fasteners down to the 33Nm setting. This time I did 59Nm. Any insights as to what the "white chrome plated" and "white" refer to? Does it refer to the link material? Not sure how that could drive a nearly 2X difference in torque values.

I will eventually get to those rear subframe bushings because I do think the deflection shown in my earlier pictures is excessive. But I'm in the process of selling the house and moving and it may have to wait until that is over... I'm done battling the snow every year, so we're going to try California.

Scott
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Re: Subframe Bushing - Source of Clunk Noise

Post by sansouci »

Ever try to mount a goPro type camera to check your suspension movement? Might be useful. BTW the news has everyone leaving California. No water, no electricity, too hot, etc. Good luck with the move.
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Re: Subframe Bushing - Source of Clunk Noise

Post by Sbeaud »

That's a great idea Ken. I've seen plenty of videos done that way, but my brain just did not put two and two together. I actually have a gopro that I could have used. Would have saved me the embarrassment of having the easiest fix being overlooked.

On the move - yes, it appears we'll be swimming against the current tide. We'll only be dipping our toes in since we'll be renting for a while first. So many questions around a big move - affordability, safety, attitudes/friendliness, etc. It will be interesting. Unfortunately moving is also quite expensive. I think I may try to economize a bit by driving the M6. When I shipped it here to Detroit from Sacramento in May, 2019 it was $1740, but the latest quote to ship it back (same broker) is $2425. That's almost 40% more! I'll need to find some cheap all season tires to be safe. Driving in mid-November on summer tires around here would be risky.

Scott
1988 M6
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