Rear end instability
 

I've got an odd one.
I'm looking at a W211 E55 (2004) that has a large amount of bump steer from the rear end. It's most obvious if you hit a pothole with the LHR wheel whilst turning right at 30+mph, it feels like the rear end jumps a foot or so then regains traction. It will however do it whilst turning left, turning right is just easier to reproduce nearby.

There isn't any obvious wear or play in the rear suspension (50k mi), it's currently setup with factory toe in to spec. Not lowered and running factory rims with 275/35/18's. It does this jump in all suspension modes and heights and can be easily reproduced. I've read alot about the Renntech and Evosport toe links from other posts but in this case I'm not certain they will rectify the problem as I dont have a problem with straight line accelleration (yet?). I'm considering temporally increasing toe-in well beyond specs to see it if reduces the problem but I was wondering if anyone else has come across the problem. I've come acroos this before with W211's but it's usually a wheel alignment issue or a worn component but I have neither in this case.

Any thoughts? :nix:

Have you checked the rear subframe mounts , there has been some fail and would cause the symptoms you have .
Marc

All subframes bushes and control arms are fine, thats why I'm stumped, I can usually find a reason for this sort of issue pretty easily

Do you own this car or are you looking at purchasing it? I can recommend a good mechanic who's knows these cars and could work the issue out if you want?

Nah, its a car I'm working on. I'm a MB tech myself, it's just a problem that being a bit more difficult to locate than usual that I'm bouncing ideas about.

I know assumption is the mother of all f-ups, but have checked:

1. With the car on the lift, is there any play in the rear suspension?

2. Tire inflation?

3. Are the tires old and hard (too many heat cycles)?

4. Determine if the problem occurs in Comfort, Sport 1 and Sport 2 settings?

5. If the tires are rotational, are they rotating in the proper direction?

6. Bearings?

Maybe you fixed this already, but is the suspension bush worn at the top of the strut?

Lift the car and push down hard on the wheel hub.

The suspensions bushes normally push the wheel upwards and compress the strut bush, but if you overcome that pre-load, any play in the bush will be very obvious

Cheers, Nick