Hi, just after some ideas really, I have a 2007 Xk and have an intermittent wheel shimmy when braking from around 60mph down to 30mph.. in warmer weather it starts to do it after 4/5 miles, now it's winter in the UK the issue has all but gone, I'm thinking it may be the bushes in the lower control arms (banana arms?) ie the cooler weather means the rubber in the bushes stay harder for longer meaning the shimmy is less noticable? I had a BMW e38 a few years ago and it had similar issues, has anyone else had the same or similar experiences on their XK?
I've had new front discs and pads, dont think it'll be the discs as the shimmy is intermittent.. the tyres were new when I purchased the car a couple of years ago and the alloy wheels themselves have been refurbished before my ownership.

thanks in advance.

 

I had a similar problem, I used a dial gauge to find that one area of the inside of one of the front discs was a couple of thou out even though the discs were in really good shape otherwise.

 

I replaced rotors+ pads. When I purchased my 2008, after 15k miles I was always fighting an elusive shimmy on braking. I measured runout and it was minimal. Replaced rotors with some brembo units and shimmy is gone.
ymmv
WJ

 

Thanks, the car is due its annual MOT next month, I'll ask them to have a look at the disks/rotors as they should still be under warranty.

It does look as though it's been a long term issue as it has had around 4 sets of discs and pads in the last few years. For reference it's done 118000 miles and on a motorway run at normal speeds it's doing close to 35mpg so don't think it's a sticking caliper either. Can't remember the make of the discs on currently but I was thinking of changing to brembo's

 

You mentioned the magic word. 60mph. Rebalance the front tires. Inspect the outer tierods if they can. But my money is on the balancing.

 

A pulsating brake pedal (wheel shimmy) can be caused by random brake pad deposits that have accumulated on your rotors. This happens when you keep your foot on the brake pedal when the brakes are hot and you're stopped waiting for the traffic light to turn green. And no, your rotors aren't "warped". Brake repair folks tell you that to sell you new rotors; truth is that it's not easy to warp cast iron.

An "Italian brake tune-up" may be in order to remove brake pad deposits that have accumulated on your rotors. It's those high spots that make your brake pedal pulsate and steering wheel shimmy when stopping. Here's how to do it.

On a highway, accelerate to 70mph (or the speed limit, if less) and stop rapidly without locking up the brakes or activating the ABS (anti-lock brake system). Do not keep your foot on the brake pedal after you come to a stop, as this can cause pad material to adhere to the rotors. Repeat this 10 times and then let the brakes cool off for at least 15 minutes without stepping on the brake pedal - just leave it in Park on a level surface. Then drive your car normally and see if that stopped the brake pedal from pulsating. If it did, you got lucky.

 

There is a difference between pulsating brake pedal and wheel shimmy. The first is usually the disk is warped, and the latter is usually wheel balance incorrect, or tie rod wear. Davehxk is most likely the latter.

 

Always good to check your basics:

 

When you step on the brake pedal and the steering wheel shakes back and forth that's wheel shimmy caused by brake pad material fused to the rotor. If you believe that a high spot on a cast iron brake rotor means that it's warped, then we agree. But if you believe that a warped rotor means that it's bent, then you're mistaken - unless that rotor was extremely low quality, defective, and abused.

Ask a metallurgist. You simply can't get a quality cast iron rotor hot enough by street driving to make it bend. (Unless you abuse the $*&##@ out of it on a road course racetrack, which is where you can get the rotors so hot that they will glow red hot and bend!).

 

"Warped" doesn't mean 'bent by heat', it means "out of true".
So yes, you can still use 'warped'.

I've done the forbidden and have had my rear rotors turned. Still within spec of course, and they worked fine. I did that so I'd know if that was actually the problem, and it was. I have purchased new rotors since for those rears, but still haven't had the requirement to install them. I do monitor them, of course.

 

I'm with @sony2000 , as these are the cheapest and easiest first steps. Balance the front wheels and ask them to check the tie rods while the wheels are off. Half the places that sell tires now, will rebalance for free if you bought from them. Keep us posted please?

 

Bad wheel bearings also, but those are a bit easier to diagnose with the screeching rumble and such.

 

I have booked it in for an MOT in two weeks time, asked them to check see how true the discs are, as the discs are less than 12 months old they should still be under warranty. I've had one of the wheels rebalanced as I had a nail in it, didn't make any difference, one thing that has improved it slightly is increasing the tyre pressures 4lb over the recommended amount..

I'll will update after each thing that i do.

 

Afternoon, as requested an update on the wheel shimmy on my XK.
It passed its annual MOT today without any advisories, no issues with the brake discs or any of the bushes.
my next step now will be to change the front tyres as the previous over put a cheap make on, thinking if the quality isn't great there could be too much flex in the sidewalls.

Regards Dave.

 

Had a similar problem with a BMW E36. Never failed any MOT, our mechanic couldn’t find the problem. Replaced the front discs and pads, problem gone.

 

You are changing the tires soon, REQUIRE an inspection of BALLJOINTS and TIERODS on your front suspension.
Changing tires will balance the other wheel that you did not do, and eliminate the possibility of a broken belt in a tire.
After that, the only thing left to check are the mags themselves. Since they have a history, ask to have the mags checked for BENTNESS. when spinning them for balancing.

 

Another cause is simply leaving the car outside in damp conditions. The pad material rusts onto the disc leaving a pad-shaped shadow. If the corrosion is shallow it more or less wears away fairly easily but the longer we leave it, especially in northern European climes, the deeper that rust goes and it becomes hard to remove. Ferrous oxide is harder than cast iron and more voluminous, so what you get is nodules of rust embedded in the disc which are then higher than the surface as well. The pads ride on these and can't wear them down properly. Eventually the whole disc goes like this and the frictional characteristics of the disc drop noticably. The pinpoint local heating causes the CI to heat locally and turn into cementite which is really hard and has low friction and makes the disc even worse. Often the reason why swapping the discs out makes the braking feel better because it really is better, but not because the previous disc were rubbish but because they have "aged" with use.

If a disc has such a high point it will result in a steering shimmy. If both front ones do, and they happen to be in sync, it feels like the shimmy has virtually gone, only to return as the two discs go out of sync again. If it is the rears, the body of the car shakes and the steering seems OK. Sometimes it is just a matter of using the car very often and all will be well. If there is shimmy on new discs, there is most probably a problem somewhere else.

The Zimmermann disc, Jurid ceramic pad combination on the rear axle of my daily has gone this way after just two years. The original discs and pads were OKish for 5 years. Next time I'm going to try ATE discs which are high-carbon for this fit and switch back to non-ceramic pads, also from ATE as it happens, as ceramics always seem to cause me corrosion problems on rear discs.

 

Davehxk would feel that disk condition in the brake pedal. He doesn't. So not a possible cause.

 

Hi, I had new discs and pads last year and the issue didn't really go away. When I brake I don't feel any sensation through the brake pedal that would indicate warped discs.

The steering wheel shimmy/shake only happens intermittently when braking, but usually at some point on each journey. It does seem better in the colder weather but if I go out for a drive the first couple of times when I brake it doesn't do it, then after a while it does. I'm just trying to work my way through things and will hopefully find a fix and report back.. It's annoying, if I have it on every journey from start to finish it would be easier to find the fault! The next task will be to change the tyres for a better make, as well as a wheel refurb, so then i know i have a decent set of wheels/tyres, recent discs/pads. After that I'll look at suspension bushes but they all look good.

Thank you for everyones advice so far though

Dave.

 

Hi, just thought I'd bump this thread

as you've read in my previous posts I've had an intermittent wheel shimmy on my XK for quite some time. Well today I've fixed it! the root cause seems to have been the front discs and not a suspension bush as i had thought. What helped to diagnose it was buying a new set of tyres (Bridgestone potenza sport from Costco, they were doing a deal, buy 4 and get £120 off total price) these seem to have a firmer sidewall and the intermittent shimmy was not intermittent, it was all the time, with newer and better tyres there is a lot more feedback and you could just 'tell'.
I changed the pads and discs this afternoon and have been for a 50 mile drive and all seems well.

Thanks everyone for their help/advice, i couldnt understand why I was driving the same route but not getting the shimmy all the time, that's why I thought it was something else other than discs/pads.

For reference
old tyres front - city racing (I know, they were new tyres put on by the garage I purchased the car from) and Dunlop rt2 at the back.
front discs/pads - Pagid
now
Bridgestone potenza sport all round
Discs - ridex
Pads - mintex.

Regards Dave.