What is wrong with my rear suspension?!

"RyanFrew" (ryanfrew) 05/18/2016 at 11:16 • Filed to: Halp!

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I have now had my ‘05 Mini Cooper S into BMW once and my local mechanic twice. All three times, I was told that they couldn’t find the problem. Basically, there is a loud knocking coming from the passenger-side rear suspension. Sometimes it sounds more like metal on metal scratching, almost like worn out pads on the rotor. The sound got worse yesterday after I slowly navigated over a couple of speed bumps. It’s also definitely worse at slow speeds than on the highway, and especially bad over uneven pavement. Here are a few diagnoses that I’ve already gone through:

With the car in the air and on the ground, there is nothing loose enough to wiggle it by hand.

The caliper is tightly secured

I have aftermarket end links which appear to be in good shape. They’re 2 years old.

The rear sway bar and sway bar bushings were replaced this week. I wanted a larger sway bar anyways so I was crossing my fingers that it was the bushings.

The car feels great. Steering is very tight

So what does that leave? Control arms? Shock/strut? How would I know if they’re bad? Agghhh!

SidewaysOnDirt still misses Bowie > RyanFrew 05/18/2016 at 11:20

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Bad caliper or bearing. Probably caliper.

RyanFrew > SidewaysOnDirt still misses Bowie 05/18/2016 at 11:23

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Caliper? Making noises over bumps, regardless of whether I’m on or off the brakes? How could that happen? Bearing is intriguing, but I don’t feel any play in the wheel when the car is in the air.

derf > RyanFrew 05/18/2016 at 11:34

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Loud knocking over bumps could mean the rear shock mount’s let go, but if it’s been in three times I’d think it should have been checked.

Textured Soy Protein > RyanFrew 05/18/2016 at 11:42

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Not sure if this is a common issue on the Mini, but on the E9x 3-series and E8x 1-series, the stock rear upper shock mount bushings are made from a very soft material (the theory is BMW did this to counteract the terrible ride of run-flat tires) and can go bad in well under the 10+ years your car has been on the road.

Looking at the parts diagram for your rear struts, there’s an upper shock mount (“guide support” in BMW parlance) that includes a couple bushings. Part #10 on the diagram.

Looking at these pictures, the material looks very similar to me to the stuff in the 1- and 3-series rear shock mounts.

So, if I were to make a halfway-educated guess, it might be time for new rear upper shock mounts. They include that metal plate and the 2 bushings. Part numbers are 33526754124 for right side and 33526754123 for left side.

RyanFrew > Textured Soy Protein 05/18/2016 at 11:53

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I think this might be the ticket!

Meatcoma > RyanFrew 05/18/2016 at 12:37

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My wife had a sound like that. It turned out one of her caliper bolts had backed out and run off. Driving forwards, when you hit a pothole or a bump it would make a knock noise but did not do it when you applied the brakes as you went over them(obvious reason). Each time I had looked at it before I figured that out everything looked fine. Once I figured out that it did not make that sound when you hit a bump with the brakes applied, I knew it was related to that caliper, pulled the tire off, started looking around and then checked the bolts and found one missing. After replacing it, I have yet to hear it again. If I hadn’t decided to check the bolts, I wouldn’t have found the issue because the pads held the caliper tight to the rotor.

Meatcoma > Meatcoma 05/18/2016 at 12:41

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Only reason I checked the bolts is because my mother in law had recently had her brakes done and while I was driving her car(figures), one of the bolts weren’t properly tightened and had taken off as well and the caliper pulled off the rotor and locked up against the inside of the wheel while I was driving. Horrible feeling, hearing that metal on metal. I thought I’d sheared an axle or the front drive shaft until I got out and looked around and seen the caliper stuck against the inside of the wheel.

Nimbus The Legend - Riding on air like a cloud > RyanFrew 05/18/2016 at 16:04

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My Friends Mini has this same problem

RyanFrew > RyanFrew 05/18/2016 at 16:09

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Kinja’d

RyanFrew > Textured Soy Protein 05/18/2016 at 16:10

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I ordered new polyurethane bushings. Expensive, but it shouldn’t necessitate replacing the metal mounting plate, which is nice.

Textured Soy Protein > RyanFrew 05/18/2016 at 16:25

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So...you may want to reconsider that. The very first forum thread I saw about someone putting poly bushings in their upper shock mounts on an R53, a whole bunch of other people were like, “those will break your shocks.” Dunno what the deal is there but something to bear in mind. Also while some bushings like control arms and whatnot are good to do in poly, with shock mounts you can get a lot of additional NVH transmitted into the car.

On the E8x/E9x cars, Monroe makes replacement rear upper and lower shock mounts that have harder rubber than the OE BMW shock mounts without going to full poly. Those are a very common upgrade.

Monroe also has a rear upper shock mount kit for your car, it’s Monroe part # 908911 .

RyanFrew > Textured Soy Protein 05/18/2016 at 16:47

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Well, shit. I really appreciate you sharing that info. It’s only 70a, which isn’t very hard, but that’s pretty strong negative feedback on the forum.

Textured Soy Protein > RyanFrew 05/18/2016 at 17:07

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All I can tell you is the E9x/E8x folks really like the Monroe ones. I’m going to be putting them on my 335xi soon. I’m doing poly in some other places like control arms, rear subframe bushing void inserts, sway bar bushings, etc. but wanted to keep rubber for the shock mounts.

RyanFrew > Textured Soy Protein 05/18/2016 at 17:10

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Sold!