Squeak in Rear Suspension

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528i-1981
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Squeak in Rear Suspension

Post by 528i-1981 » Fri Apr 10, 2020 8:39 am

There is a long-lived squeak that I've always assumed was a rear seat issue, but after removing both parts of the rear couch it's evidently something different. The shoulder bracket for one of the rear seat belts was squeaky, but with that fixed there's another squeak that is originating from the rear driver-side wheel. When that wheel travels over bumps, the squeak occurs, but not so with the other three wheels. Independent suspension is nice for diagnosis here.

The squeak is sharp, like a chirp, and is regular in tone and quick in duration. Over a series of bumps, there's a series of chirps. It is not a groan or a scrape or a rattle. I drove with the doors ajar to make sure it wasn't related to door stuff. It is not replicated by moving the body while the car is parked. It is not coming from the B-pillar, which I understand is an issue on E28s.

The car has new shocks and an upgraded ST swaybar.

I'm going to be away from the car for a few days so I can use any ideas to formulate my plan of attack. Are there rear subframe bushings that might create this squeaking? Thanks in advance!

Eric
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1981 528i Manual

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Re: Squeak in Rear Suspension

Post by 528i-1981 » Sat Apr 11, 2020 8:10 am

The subframe rubber mounts are pricey, so I'm hoping they're OK. It could be trailing arm bushings, or the shock mounts. My understanding is that the bushings should create more of a creak/groan than a chirp/squeak. The shock mount seems to place the noise right at the rear seat. Any experiences with either would be appreciated. I'll start with some tightening and some rubber conditioner to see if that helps.
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1981 528i Manual

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Re: Squeak in Rear Suspension

Post by HB528i » Sat Apr 11, 2020 4:49 pm

I would check shock mount first.

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Re: Squeak in Rear Suspension

Post by Lock » Tue Apr 21, 2020 12:43 am

I have a similar squeak to what you've described from the passenger side rear wheel, which I have believe is one of the trailing arm bushings. Unlike yours I can hear it when the car is stationary and I rock the car on the rear corners. When I'm under the car the squeak is hard to pinpoint because it echos, but i'm pretty sure it's the trailing arm bushings as they are visibly worn. I plan to replace all the bushings at some point.
Unlike yours, I also can't hear it from inside the car really. What happens if you detach your rear swaybar and rock your car while stationary - to allow free and further movement of each trailing arm (depending on how much give your shocks have). Maybe it would chirp then while you're under it?
1979 528i 5-speed conversion G260/6, Motronic 1.3 179
1980 Honda CX-500

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Re: Squeak in Rear Suspension

Post by 528i-1981 » Tue Apr 21, 2020 6:46 am

Thanks Lock. When I replaced the shocks last year I replaced the front mounts but cheaped out and reused the rear mounts. I've ordered new ones along with the rubber mountings for the shock rod. When I'm replacing the mounts I'll have a close look at everything, including the trailing arm bushing and sway bar mounts. Maybe the added rotation of the trailing arm with the shock off might help with the diagnosis. My chirp doesn't appear so much with rocking the car, but with a sharper loading, such as dropping a knee on the bumper or jumping onto the rear door sill, but only on the driver's side. I'll need to have it on ramps to be able to (carefully) provide that kind of loading with me underneath of it. I picked up a mechanic's stethoscope so hopefully that will help. It has not really helped inside the trunk or cabin.

-Eric
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1981 528i Manual

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Re: Squeak in Rear Suspension

Post by 528i-1981 » Mon May 18, 2020 5:57 am

I removed both rear shocks and replaced the mounts, rubbers and gaskets. Also inspected and lubricated the trailing arm mounts and swaybar mounts. Still squeaking with full force and vigor.

What I noticed is that the squeak diminishes over the course of a drive. I'm suspecting broken spot welds behind the rear seat. Hopefully I'll get a chance to investigate this week - if I see shiny metal, I'll have my answer.
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Re: Squeak in Rear Suspension

Post by Lock » Tue May 19, 2020 12:48 am

Strange that it lessens during a drive. Any luck having someone shake the car and you underneath to pinpoint it? The other thing is all of those pieces of metal are great at transmitting vibrations and sounds to different locations away from their origin.
Could it be the subframe bushings, the whole thing rocking slightly? Or just the trailing arm bushings, perhaps broken internally and instead of one piece metal-rubber-metal, the inner or outer rubber has torn away from the metal and on a particularly hard bump shifts and chirps?
As mentioned at least looking behind the seat is easy to do.
1979 528i 5-speed conversion G260/6, Motronic 1.3 179
1980 Honda CX-500

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