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  #1 (permalink)  
Old 05-17-2022, 06:38 PM
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Default Persistent 'clunk' coming from the PS rear

I have a BDR 2011 build with the BMW rear end (IRS with separate springs and shocks). On aggressive low speed cornering, I hear a 'clunk' coming from the PS rear while turning right. Again, this only occurs when the turn is aggressive and at relatively low speed (~30 - 40 MPH). I've gone underneath to confirm that all bolts are tight and that all bushings are in good shape. The shocks are bolted securely to the frame.

One thing that I cannot check is the upper spring mount to the frame. I can't see anything with the wheel off while conducting an inspection through the wheel well. I've tried going into the trunk to see if I can find some sort of mount that secures the upper shock to the frame. Nothing that I can find that is accessible for viewing the mounting. This is the only thing that I haven't been able to confirm out of all the rear suspension and drive train components.

And yes, I have checked the 14mm bolt that secures the diff to the sub frame. All good there.
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Old 05-17-2022, 07:34 PM
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Check the nuts on the forward trailing arm mount. They point down and the frame has slots for toe-in-out adjustment. If the nuts are loose it will shift around on side loads.

Also check the outboard axle bolt (yours should have a bolt, early cars had a retaining nut) under the pin drive hub to see if it has backed out allowing your hub and brake to slide in-out. The caliper probably won't keep the wheel and hub from fully exiting the car if it comes fully undone.

The rear spring lower perch rubber pad disintegrate over time as well as the rubber bushings in all the suspension pivot points but that is a sloppy handling issue usually not a clunk.
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Old 05-17-2022, 08:05 PM
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I should also mention that I will sometimes hear the 'clunk' when the PS rear tire goes over a big bump or hits a pothole.
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Old 05-18-2022, 12:39 PM
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Check to make sure your upper shock bolt isnt broken as well. I had that happen once and chased the clunk for weeks. Due to design, the bolt stayed in place due to the pressure the shock put on it but was snapped off where the threads meet the shoulder. This would be more in line with hearing a clunk over bumps or potholes as well not just cornering
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Old 05-18-2022, 10:13 PM
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Any inputs as to how and where I can inspect the upper spring mount where it attaches to the car frame?
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Old 05-19-2022, 11:40 AM
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Quote:
Originally Posted by SBSerpent View Post
Any inputs as to how and where I can inspect the upper spring mount where it attaches to the car frame?
Did you pull the carpet back a bit in the trunk?
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Old 05-19-2022, 09:13 PM
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Did you pull the carpet back a bit in the trunk?
I did not. I was just feeling around to see if I could find some sort of recess or hole or indentation underneath the carpet.
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Old 05-21-2022, 06:31 PM
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Quote:
Originally Posted by spdbrake View Post
Check the nuts on the forward trailing arm mount. They point down and the frame has slots for toe-in-out adjustment. If the nuts are loose it will shift around on side loads.

Also check the outboard axle bolt (yours should have a bolt, early cars had a retaining nut) under the pin drive hub to see if it has backed out allowing your hub and brake to slide in-out. The caliper probably won't keep the wheel and hub from fully exiting the car if it comes fully undone.

The rear spring lower perch rubber pad disintegrate over time as well as the rubber bushings in all the suspension pivot points but that is a sloppy handling issue usually not a clunk.
Can I inspect the axle bolt/nut by just removing the plug at the end of the hub?
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Old 05-21-2022, 08:32 PM
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Yes if yours has the axle nut, the nut top is pinching into a depression on the axle. (hammered in with a punch after torquing) You should able to see it.

If yours has the bolt attaching to axle, hopefully the installer applied a slippage mark to the edge so you can see if it rotated. Does your car have an integral hub / pin drive assembly? If yes it has the bolt type axle attachment.
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Old 05-22-2022, 01:42 PM
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My upper and lower rear spring pads are shot. Actually they are more like a ~1.5mm gasket. The bottom pad has disintegrated.

Found this researching spring pads. I don't recall hearing a right turn clunk but might be something for you to consider...

https://chrisparente.com/2013/09/08/...my-bmw-e36-m3/
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Old 05-22-2022, 06:06 PM
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I must be missing something here. In order to hear a 'clunk', I would think that the spring would need to come off it's bottom seat and then back down to create the clunk sound (assuming that there is no pad there at all). However, while driving, the spring is always under compression, regardless of hard turns or bumps in the road.

For example, even when you lift the car, the spring is still under compression due to the restraint of the shock absorber.
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Old 05-23-2022, 03:25 PM
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Quote:
Originally Posted by SBSerpent View Post
I must be missing something here. In order to hear a 'clunk', I would think that the spring would need to come off it's bottom seat and then back down to create the clunk sound (assuming that there is no pad there at all). However, while driving, the spring is always under compression, regardless of hard turns or bumps in the road.

For example, even when you lift the car, the spring is still under compression due to the restraint of the shock absorber.
Posted the link because that person said it fixed his clunk.
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Old 05-23-2022, 05:21 PM
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Quote:
Originally Posted by FlyingGumby View Post
Posted the link because that person said it fixed his clunk.
Have you ordered new pads? If so, then what is the part number and from where did you order?
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Old 05-23-2022, 06:31 PM
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Originally Posted by SBSerpent View Post
Have you ordered new pads? If so, then what is the part number and from where did you order?
I plan to raise the rear end 15mm+ so looking at these...

https://www.ecstuning.com/b-uro-part...531135420~uro/

https://www.ecstuning.com/b-uro-part...531136385~uro/

Guesstimating ~10mm thickness combined. I have enough collar adjustment to lower to current height (with pads) or jack up another 30mm.

Can report back after I have things back together in a week or 2.
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Old 05-23-2022, 07:29 PM
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Originally Posted by FlyingGumby View Post
I plan to raise the rear end 15mm+ so looking at these...

https://www.ecstuning.com/b-uro-part...531135420~uro/

https://www.ecstuning.com/b-uro-part...531136385~uro/

Guesstimating ~10mm thickness combined. I have enough collar adjustment to lower to current height (with pads) or jack up another 30mm.

Can report back after I have things back together in a week or 2.
On our BDRs, can the spring be removed by just unbolting the rear shock and allowing the arm to come down or is a spring compressor required? The article said that the spring comes out easily but I'm wondering if that applies to the BMW only.

Also, do these pads come in various thicknesses?
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Old 05-23-2022, 08:05 PM
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It's doable... if the you disconnect the other shock as well so you won't be fighting the sway bar.
You can slip a jack handle in the pin drive hub and step on it for leverage.

If it's still too tough. Loosen all 4 swing arm bolts one turn (Upper inbd/outbd and Lower inbd/outbd) so you won't be fighting the bushings (rubber are worse than Poly) that will resist rotation.

Last edited by spdbrake; 05-24-2022 at 06:23 AM..
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Old 05-23-2022, 11:04 PM
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The smallest upper pad is 5mm thick and comes thicker in 5mm increments. Think the bottom is one size. I thought about using different size upper pads on the bottom but concerned the spring would slip off the perch. The bottom pad looks secure.

I suppose you could also craft something out of different material to get the thickness you want. The original gasket like material lasted 10 years but probably failed sooner.
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Old 05-24-2022, 02:35 PM
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Quote:
Originally Posted by SBSerpent View Post
On our BDRs, can the spring be removed by just unbolting the rear shock and allowing the arm to come down or is a spring compressor required? The article said that the spring comes out easily but I'm wondering if that applies to the BMW only.

Also, do these pads come in various thicknesses?
I recall trying to remove the springs last year and gave up because removing shocks and sway bar mount was not enough. The upper treaded collar keeps the spring from coming out easily. BMWs don't have this. Had not considered just loosening bolts per spdbrake. Worst case would be unbolting things until you get enough clearance which is not hard but time consuming.
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Old 05-24-2022, 07:19 PM
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Quote:
Originally Posted by FlyingGumby View Post
I recall trying to remove the springs last year and gave up because removing shocks and sway bar mount was not enough. The upper treaded collar keeps the spring from coming out easily. BMWs don't have this. Had not considered just loosening bolts per spdbrake. Worst case would be unbolting things until you get enough clearance which is not hard but time consuming.
But you were able to do it judging from the photo of the rear spring and the damaged pads that you show a few posts back....
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Old 05-24-2022, 09:28 PM
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Using a floor jack underneath the lower swing arm to jack up the assembly to compress the spring and then using multiple, heavy duty zip ties around the compressed coils should make removal of the spring easier, don't ya think?
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