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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > How to tell if a rear suspension bushing is good?



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      08-02-2022, 06:58 PM   #1
rararat4
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How to tell if a rear suspension bushing is good?

I am sorry if this has been handled before but I could not find anything reasonable and useful on the topic.

I need to change scratchy ball joints in the rear of my 2009 328i. The car has 254000 kms on it.

I am considering if I should buy a tool for the purpose from ECS Tuning. Since it is pretty pricey I am wondering if I should also then change any of the other bushings in the rear suspension. I do not have any clunking or obvious play in the rear.

In all the other threads that I examined people talk about pretty much arbitrarily replacing or upgrading this bushing or that. So to cut to the chase, I would like to hear from people who replaced the inner bushing on the control arm and either one or both bushings on the lower trailing arm, the one with large holes. Was there play in the old bushings or they seemed pretty tight after removal?
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      08-10-2022, 02:48 PM   #2
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Check this video for clues: https://youtu.be/I0xOo3D9OrQ?t=741 (starting at rear axle)
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      08-10-2022, 03:32 PM   #3
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I think I've posted similarly before:

It depends on what you want out of the car. If it's a stock road going daily driver, those bushings last a LONG time. Yes they will wear and soften, but you'll almost certainly never notice the difference in changing them.

I'm over half a million km, and all the joints and bushings are from Munich in 2006 except the front strut rod bushings, shocks, and upper shock mounts. The car is taunt, rolls and steers just like it should, and is a joy. Could it be better? Maybe...

Racetrack? well that's a different story.
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      08-10-2022, 04:24 PM   #4
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Thank you Steifan. You broke up the monotony of watching the read count go up with no responses.

I had seen the video. It is typical of other discussion on the subject. It does not really address bushing wear. It is more for people who like to throw money at a problem without knowing if they need to or not.

For instance, the bending in trailing arm issue in the video. I personally do not care. This is what BMW installed on my car and therefore it is good enough for me. Steel bends a bit compared to aluminium alloys as anyone who had a few bikes will know. It makes it easier on the bushings in a car and on your back side in a bike. If I wanted M3 handling I would have bought an M3. Also, the M3 control arms might not give in in an accident or on hitting a big pot hole and you may end up with a big bill fixing the back end. But, as I said, I do not care about this issue.

I did see a good video on engine mounts recently which is a similar conundrum to the rear bushings. Here:


It is a good video in many ways even if the Bentley manual does not call for dropping the cross member to do the job. This guy shows the mounts he has taken out of his 335. One of them is broken, while the other has some play. That's what I would like to see for the rear suspension bushings.
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      09-02-2022, 04:22 PM   #5
rararat4
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So, I am done with the job of replacing the ball joints. They were gone. Under the rubber boots there was essentially just dirt softened up by my prior injection of lithium white spray. The ball joints were also loose. Beats me how it was not really possible to detect play in the rear suspension by grabbing the rear wheel and pulling on it.

The tool I bought to help replace the ball joints and bushings was the one from ECSTuning B8800101. The tool's description says it is for all the bushings in the rear trailing arm(s). I did not call the tech support prior to buying it and then paid for that oversight. Only the ball joint on the swing arm and the outer bushing in the trailing arm can be replaced safely with the tool. Perhaps, the tool is also good for the two control arms but I had no intention of touching that and there the bushings are in the control arm so, you could just buy the arms. Anyway, the inner bushing on the swing arm is a size my tool kit had no adapter for and ECS wants you to buy another tool kit worth about $200 to do that. The inner bushing on the trailing arm may be possible to do with the tool I bought but the adapter most closely matching the opening overlaps by .3 mm so .15mm on opposite sides of the diameter. I was not going to risk bending my cross member to see if it would work. The cross member is not cast iron but rather stamped sheet metal.

While the ball joints were gone, the bushings I replaced were not too bad. They were eroded where they stuck out of the opening they were in, but they were not obviously loose or broken. I could see how much flex the bushings had by putting an extension bar through them and pulling on it. I would say the new bushings were marginally stiffer. None of the inner bushings were bad either. The thing is that the whole rear suspension hangs on, perhaps 8 bushings or 10, if you count the sway bar. So, a small amount of softness in a bushing multiplied by 10 may have a cumulative effect. I will never know.
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      09-13-2022, 08:10 AM   #6
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Quote:
Originally Posted by rararat4 View Post
The ball joints were also loose. Beats me how it was not really possible to detect play in the rear suspension by grabbing the rear wheel and pulling on it.
This is likely caused by having the suspension at full droop when checking for play. This usually puts the ball joints in a bind "tightens" them up. If you were to place a jack under the LCA with the car in the air, and get the suspension back to ride height, or atleast nearer to it, you would've found the play for sure.
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