My 2003 MCS has recently developed a slight shimmy when braking at speeds greater than 60 mph, and I'm wondering what the cause and remedy are.

There's no shimmy at slower speeds; it's only really noticeable when braking moderately to heavily from more than 60 mph.

Ordinarily I'd guess that slightly warped rotors are the culprit, but it doesn't feel like that sort of shaking. Also, a superficial inspection of the rotors (running my fingers over them) revealed no noticeable ridges.

I am more inclined to guess it's something in the steering rack. I recently drove over some reasonably large (and unavoidable) potholes on the freeway going at least 60 mph. This has definitely thrown my alignment out of whack, as the car now tugs gently to the right (and will wander if I release the wheel for more than a couple seconds).

Could the presently poor alignment be the cause of the shimmy? Will having the car re-aligned resolve this issue?

 

Sounds like its time to have the complete suspension checked, it could be as simple as a blown bushing or a bad ball joint... sometimes when it is just minor undulation during braking it might be as simply or something as weird as the wheel studs where put in one at a time and the first one was torqued down and pulled the rotor untrue to the wheel hub.

Best of luck.

Motor on!

 

If you can feel 1/1000 the of an inch with you fingers, wow!!
An am alignment issue can cause issues...and trying to fix any single issue with other items masking it can make it harder...
If the shimmy I'd from a rotor, it will worsen in the next few thousand miles...
But so will tire wear from a bad alignment... So I'd have it realigned.... And see what happens....ignoring that will cost you tire life.

 

Sure sounds like a warped rotor or pad deposit to me. If we knew how many miles on the OP's MINI a more accurate guess would be possible.

Are you feeling the shimmy in the brake peddle or the steering wheel?

 

Warped rotors I believe.

 

Yup..to zippy. You won't feel the warping with a finger. Gouging on surface of rotor is not the same as warping.

 

Thanks for the replies.

The shimmy is barely noticeable, and not always evident. The car has almost 145,000 miles on it - and I hadn't felt even a hint of shimmy before this (in the six months I've owned it).

I do plan to get the alignment redone - eventually. The problem is that the expressway I take everyday is being torn up for sewer main repair - and will continue to be dug out, patched, and damaged for the next few months.

Every few days there's another pothole. Some of them are invisible or unavoidable in traffic, and I seem to hit one or two a week at 50 to 60 mph. If I get the alignment done tomorrow, I figure I'll just have to get it redone a few weeks from now. Since the alignment isn't that bad, I'm considering waiting to fix it until the work is done.

I absolutely agree that slight warping of the rotors is a possible source of the shimmy. And yes, I know I can't feel vague warping. I was only doing a gross check. (I have had other cars where I didn't notice any sort of shimmy until the rotors were truly, obviously, and tangibly warped or gouged.)

If it is warped rotors, it should get worse over time. So I'm going to keep an eye on it.

 

Warped rotors it is!

It's clearly getting worse, although it's still not noticeable unless I'm braking at more than 50 mph. Now to see about getting them turned.

 

What do you mean getting them turned?

About a month after i bought my mini, i had to change mine. Its really a PITA when braking.
Im about to change to the JWC kit. I "might" be selling mine old ones. (i replaced the warped ones with drilled and slotted.)

 

My guess, as others stated -

1) warped rotor(s). This can be checked with a gauge.
2) alignment
3) tire out of balance or defective (a bit of a long shot)
4) other suspension component worn out

By turning the rotors; that means skimming a small amount of metal off the rotor with a lathe to true them up. Many argue that it's better to just replace them.

 

Yes, turning the rotors means having them machined to be flat (assuming there's enough material left for that). In the past, getting rotors resurfaced was quite common; but I've read that many people don't advise it with the OEM Mini rotors. Of course, replacement is always also an option.