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Suspension & Braking Forum by BimmerWorld
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Old 10-24-2008, 08:05 AM   #1
peanut_man
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Join Date: Sep 2006
Location: Chicago
Posts: 256
My Ride: 2008 335i Sport Pkg
Caster out of spec. Can this cause 'bump steer'?

Hello,

I mistakendly posted this one on the general forum, sorry. Let me try again... I've been trying to resolve my 'bump steer' issue for a while now. The car is fine on flat road and will track straight, no vibration. On uneven surface, the steering tends to turn with the uneven road surface. Also when I hit a bump it would bump the steering left or right a bit. I had tried to replace the power steering pump which was whining, tie rod ends, and even tried fitting new steering rack ($285 rebuilt from ***********.com ). The twitchy feeling still there. I think I had enuf of throwing parts and guessing on the cause of the problem...

Looking at the last alignment report, however, the caster is out of spec and the print out says "the manufacturer does not specify a front CASTER adjustment" note. Attached is the alignment report.



As far as I know, caster will affect the stability of the steering. Could this be my problem with the steering? I didn't find any mention of how to correct the caster for an e46. Is there anything I can do? Also, about 2 years ago I did replaced my front lower control arms + CABs with Meyle. The steering issue seems to start since then. Could this after market part be the cause of this mis-alignment for the caster? Car has never been in any accident.

Any advice? Thanks.
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Old 10-24-2008, 09:01 AM   #2
jpr
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Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Don't worry about the caster. The values you are seeing are a reflection of the load condition of the car at the time the readings were taken. They are still within the range of reasonable expectation and even side-to-side.

As for the rest of your alignment, it's your toe readings that have me puzzled. What units of measure are being used? That is when it states "0.12in" does that mean "0.12 degrees of toe in" or does it mean "0.12 inches of toe in"? Secondly, with the E46 (as with rear wheel drive cars in general) you want to run less front toe than rear toe. So something is wrong with the cited specs and the settings they've got you at. Getting that fixed will help with your stability issues.

What tires do you have on and how many miles do you have on them? That can be a big factor in tramlining.

When were your control arms and CAB's replaced relative to your alignment, before or after? If after, then try getting another alignment. As for the parts themselves, there is likely nothing wrong with the Meyle components themselves. An installation error is more likely, but the most common mistakes will show up as front toe alignment problems.

As for the bump steer, there is a rather epic thread on chasing that sort of problem here - http://forum.e46fanatics.com/showthread.php?t=380618 - One thing to put on the short list of suspects is your strut mounts.
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Old 10-24-2008, 10:14 AM   #3
peanut_man
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Posts: 256
My Ride: 2008 335i Sport Pkg
Thanks for reply,

I'm not sure either how the alignment measurement for toe means. Here's a pic i snap of the report from Goodyear:



This was done after the steering rack was replaced, so the 'before' measurements were way off.

The tires I have are Kumho. They are the only match set that's reasonably priced that fits my sport pkg (225/45-17 fronts, 245/40-17 rears). I'm on the 2nd set now and have been using them before I started experience this twitchy problem. What would be the correct toe specs for my car?

The alignment was done just this past week. The CA/CABs was replaced 2 years ago.

Would it help if I try getting adjustable aftermarket strut mount that's more durable than the stock mounts?

Thanks.
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