I have owned my 2005 XJR for over a year now, and just recently my XJR has started to have strange braking behavior. When I apply my brakes on mild to moderate pressure, my steering wheel shakes and shimmies from side to side, about 3" total movement. My passengers also feel this side-to-side jostle. When I apply moderate-to-heavy braking the shimmie completely stops and my XJR stops properly. At first I thought I had warped brake rotors, however when I brake hard it should get worse, and not better! The shake also does not happen every time, however it happens 90% of the time when braking. I'm worried that I have something loose on my suspension. Does anybody have any idea what is wrong before I jack my car up?

TLR
Just started within last 2 weeks
Steering wheel shakes from side to side under braking
Passengers can feel car shaking
Only happens under mild to moderate braking (not under heavy braking)
Happens 90% of the time (braking in a straight line)
Worried about a loose suspension part (loose a-arm, etc)

Does anyone have any ideas?

 

Most troubles like this centre on the brake discs. From your post, it seems the car handles OK when you're not braking, so one would not normally suspect suspension bushes and ball joints at this stage.

How long since work was done on the brakes ? I would get an inspection done. Of course there is likely to be some wear in the suspension by now, which braking may accentuate. but I would go for badly warped discs, or possibly a stuck caliper.

 

X2 with brake rotors.

It sounds like they are warped so they push the pads away. As you apply the pedal the pads start to contact the warped section first, causing the intermittent pull, until you apply harder and the pads make full contact.

 

This is the first warped brake rotor I've had on a Jaguar. The brakes were inspected 10 months ago at the Minneapolis, MN dealership.

I had a warped rotor most recently on my Cadillac. As I applied more brake pressure, it would shake worse and I could feel it through the pedal. That why I leaned away from warped rotors. I will have the chance to check it out this weekend, I'll post updates!

 

Definitely a warped brake rotor, the Brembos are well known for this. Light braking shudder but smooth under heavy breaking, I've had it myself. It doesn't take much, my drivers side front had less than 1mm warp, front discs machined and it was gone.

 

There are different ways for a rotor to go bad. I suspect yours developed a wobble. The thickness if the rotor is consistent, but it is not turning true.

A second way for a rotor to go bad is if the car sits for a long time where the rotors can get wet. The area protected by the pad does not rust, but the rest of the rotor does. The rust is removed when you drive next, but now you have a difference in thickness around the rotor. This type of problem is felt worse as the brakes are applied harder.

Even though your issue sounds like a warped rotor, there is a possibility the tires can be causing a shake too. My money is on the rotors, though.

 

Sounds very similar to the problem on mine, I have checked everything and all I can find is a small amount of play in one wheel bearing (new discs etc have been fitted, x 2 sets) I can't believe that is all it is but can only replace and see.

 

Every time I had this problem with all my cars (Jaguar and non-jaguar) it ended up being loose / worn wheel bearings and/or warped rotors, 100%.

 

My S-Type did that, turned out to be a slightly bent wheel.

 

Replaced my wheel bearing today, all judder and shake under braking has gone (so far), still have a bit of vibration that comes in at 110, but it is difficult to pinpoint if it's front or rear or just the road and the suspension stiffening up, there was very little play in the bearing and it was a bit noisy when it was spun.

 

Have you removed one or more front wheel recently? If so, you might want to loosen the lugs and re-torque. I seem to need to do this every time I get mine serviced. I think they get the torque right, but don't pay much attention to the pattern.