97 Xk8, had new pads/rotors done about 5-6k ago. Before the new tires now braking vibrations at all.
Just had new tires put on the car. They are the next size up 255's.
Now ONLY upon coming off the HWY from a high speed, 60 or so when I hit the brakes I have a real tight so to speak vibration when braking. I don't feel it in the steering wheel or in the pedal but the car has a real tight yet slight vibration, meaning it is not a wobble or the like. Kinda hard to explain.
Any other braking event it is fine, just when I am coming off a high speed. The car does not shake while driving as if there were a tire out of balance.
Perhaps with the new tires and they being bigger there is a front end suspension issue that was not there before?

 

by the way, the 255 width looks NICE on the car.

 

Hmmm, sounds like maybe your lug bolts were torqued unevenly causing some slight rotor warpage. Loosen them all and retorque them with a torque wrench by hand to about 90 Nm.

Also torque them from opposite bolt to opposite bolt...do not torque them in sequence.

 

Huum, I took the car to my shop that I have been using for 25 years, an independant, not a chain shop. I can't think they would have messed them up like that!?!!?

 

Most shops put wheels on with an air impact wrench to save time...and it is easy to overtorque or unevenly torque them this way...they need to be hand torqued per the spec.

 

BRGJAG, Had the exact same problem. I also went to 255's on my '98XK8. At the time the $400 Kumho's were the only tires that would fit except for $1300 worth of Perrillis My Vibration sounded like it was coming from the right rear. I had installed drilled rotor and ceramic pads all around. After 10K miles tried aftermarket plain rotors in the rear. Heard through this forum that some of the drilled rotors are a little weak. I tried the re-torque on all wheels which didn't do anything. Finally after 6 hours at local inde.,5 hours at dealer, and switching out the after market backs for Jag parts(which made no difference in vibration so we put back the aftermarket parts) the solution was replacing the FRONT right rotor with Jag parts. Vibration sounded like it was coming from the back until someone actually sat in the back during test ride. Only then could you tell it was coming from the front. New aftermarker plain rotors in back and new Jag rotors in front and all is well. Jack
P.S. you could see a big difference in the thickness between the drilled and plain rotors.

 

BRGJAG forgot to mention, I've had the 255's on for over 60k and there hasn't been any problem other then they ride a little hard. Jack

 

so it is fair to say that they impacted then on, tweeked the rotors a little?

 

this car is that sensative to have this issue?

Yea my ride is a little hard, but got the air pressures about right, right is not bad at all.

 

It is certainly possible and it takes 5 minutes for them to retorque them by hand. If that does not fix it, then you can start digging deeper.

 

Huum, I did not have JAG rotors put on but did not have cheapo ones puton either. This car was FINE until these tires were put on and you only BARELY feel it when I am coming off the HWY or doing a high speed stop quickly, then its there, ever so slight.
If it aint something with this car at almost every turn.

 

did you get your new tires road-force balanced, or the regular dynamic kind? HUGE difference...mostly noticeable at high speeds.

 

I think the key words are "vibration when braking from highway speeds". I would forget about the tires and look at your rotors. Trying to straighten them by retorqueing doesn't always work. The damage may be done. I found 2 lugnuts that were damaged when the tech didn't put the socket on all the way. Time is money to alot of these guys. Like I said before the Jag rotors were a lot beefier then the aftermarket ones. Jack

 

WHAT? ha ha ha


Just driving the car there is not tire out of balance feel at any speek. Just coming off a high speed, hwy speeds, when I hit ther brakes I feel VERY slight vibration in the car.

 

Before resolving an out of balance front wheel, my vibration only occurred at highway speed, a sort of 'sweet spot', shall we say. Crusing at any other speed, it was not evident. Accelerating past this sweet spot, also you could not tell. Try this next time...when coming off your highway, instead of braking, let the car decelerate instead...if you sense the vibration, you can rule out brakes/rotors playing a part in that. If not, and you can verify its only when applying the brakes, then you can ignore anything I say in this one.

 

I will do this no brake roll slow down test, paying attn for anything, but thinking back to when this slow stop took place I had not vibration that I can recall but I was not looking for it then either.