M Z3 Suspension / Subframe Knock - Bimmerfest - BMW Forums

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E36/7 Z3 (1996-2002)
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Old 08-27-2010, 01:56 PM
S54 Roadster S54 Roadster is offline
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Location: Toronto
Join Date: Apr 2010
Posts: 2
Mein Auto: 2002 M Roadster
M Z3 Suspension / Subframe Knock

2002 M Roadster @ 30,000kms

Background on the car:
-Car is stock
-BMW dealership had the front sub frame apart to pull the oil pan to diagnose spun con rod bearing
-Engine was replaced this spring as goodwill gesture by BMW despite being 2 years out of warranty (I would be happy to share the details of this if others are interested)

Car has developed a deep sounding knocking noise when the weight of the car is shifted. This only happened recently after a short drive on a rough road. Its most easily replicated by driving at low speed and quickly turning left to right. On each change of direction there is one loud knock heard from I believe the front of the car. I have replaced the stabilizer bar links and checked all other suspension/ subframe components for tightness. It is impossible to replicate the noise with the car stationary. There is no play in the steering and no noise created from turning the steering while stationary. A rattle can also be heard when going over bumps. Below is what I have observed from both.

Knock present when turning. More specifically, once sufficient load shifts. For example, you can slowly turn the wheels when moving, but unless you give the car some gas, or turn wheels more quickly it will not knock. It feels like it requires a specific amount of load to be applied while turning in order to knock. Alternatively, if you quickly dart the wheel back and forth the knock happens each time.

Knock/ rattle present when going over speed bumps but only when you hit the speed bump at an angle and the two wheels go over at different time. When you approach the speed bump head on and both wheels go over at same time there is no noise heard. However, when you go over at an angle (even with the wheels straight to the car) a rattle / knock is heard when each of the front wheels goes over, and again when the rear wheels go over (provided the rear wheels also go over at different time) This noise still sounds as if its coming from the front even though its triggered by the rear wheels.

What I have checked:
-Stabilizer bar links (replaced)
-Checked stabilizer bar bushings
-Tightened all suspension, subframe components and the engine mounts
-Checked the FCABs
-Checked the bearings in the top of the shock tower, they seems to rotate freely
-There is no play in the steering when using manual effort to move the wheels back and forth when jacked up

Any suggestions? Thank you.
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Old 03-09-2011, 06:03 AM
wannaberockstar wannaberockstar is offline
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Location: St. Louis, MO
Join Date: May 2008
Posts: 6
Mein Auto: 1998 Z3 2.8
Have you had any luck with this? I am having a similar issue and would love to know what you did to fix it.

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Old 03-09-2011, 06:17 AM
S54 Roadster S54 Roadster is offline
Registered User
Location: Toronto
Join Date: Apr 2010
Posts: 2
Mein Auto: 2002 M Roadster
Yep it was the steering rack.

The dealer spent 5 hours trying to diagnose it but could not find anything.

I ended up figuring it out myself. With the car parked I reached under and held the tie rod, another person quickly turned the steering wheel back and forth about 1/16 turn. Doing this reproduced a knock coming from the rack.

There was absolutely no play in the rack otherwise which is what made it hard to diagnose initially.

The rack from BMW is around $2000CDN but Auto Parts Warehouse has a few options for between $350 - $600. I put the car away before I had the chance to have the repair done but plan to this spring.

Let me know how you make out.
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