I 98 xk8 brake pedal has pulsation and front shimmies hard when braking. So I replaced all four rotors and pads. still continued. took to friends shop they thought I got warped rotors, so I returned them 2nd set still same. I then changed inner and out tie rods. still the same. took to another shop that had a pro cut machine to clean any run out in rotors and did alignment. no change.
then took out fuse for ABS fuse #4 no luck. Both shop and myself can't find anything loose in front. wheel bearings feel tight car has 75000 miles Any ideas? thanks jimmy

 

Are the calipers free to move? Are the caliper mounts bent?

 

Maybe the best place to look now would be wheels and tires. Any chance of a distorted or damged rim? Do the tires seem normal, especially wear pattern? Feel around the inner sidewalls for anything unusual.

Suggest a run-out test on the rims. If your tires are not directional, you might swap left to right just to see if any effect. If the front and rear sizes are the same (I think they are on your car), swap front to back.

Good luck,

 

It was late and I forgot to add: Are the pistons free in the calipers or are they sticky.

Get the wheels off, snug the rotors down and turn them and watch what happens. Step on the brake and see what it takes to get them moving freely. They should just have a slight drag or loose when you try to turn them by hand. They shouldn't bind. Look for pinched or bad brake lines or hoses.

When you replaced the old pads did they have a funny wear pattern. LIke more wear on the front of one and more on the rear of the other?



PS Did you check for loose wheel bearings or bad ones?

 

Dennis 07:
If you folks in New Jersey get tired of Danielle Staub, send her to Southern California. She'll fit in here and they could put her on Real Housewives of Beverly Hills or Orange County. LOL

 

Afraid I don't know the lady, but from your post I'm thinking she must be from that "real housewives of ... " thingy.

Not so fast: we don't part with our cultural icons lightly!

 

Just in case: when I said step on the brake pedal, I meant for it to be released before trying to turn the rotor.

 

unless someone knows how to use a dial indicator your spinning(or shaking your wheels)
Take the wheels off torque (with a torque stick or torque wrench)all the lugs. Then measure the runout with a dial indicator out towards the edge of the rotors. I personally want .002" or less. I many times find higher like .006-.012. then pull the rotors and check for rust on the hub(likely in STL since I grew up in Ballwin and my parents still live in Town and Country off Ballas) clean the hubs and you definitly dont want more than
.002 here. Any more, replace the hub. and recheck the rotors after. And amount of runout on the hub like .002 will be something like .008 or higher out to the rotor edge. Jag spec is something like .006-.008 on the rotor but if youre feeling it you need to check. And what condition is the upper strut mounts and control arm bushings? These at your cars age can definitly lead to funny handling especially when braking which throws the suspension the most stress it sees past hard cornering. Anything worn or loose will be more pronounced under braking when trying to slow the entire weight of the car at speed.

 

good suggestion on the rusted hub, if the wheel came off one way, then back on a different way (1 in 5 chance in getting it on the same way?...I was always bad at statistics) and there is any corrosion it, that'll definitely cause an imbalance, probably felt at highway speed in addition to braking though.

Any chance there is air in the brake lines?

 

I think that Brutal is talking about looking for stuff between the rotor and the hub. That could cause the pulsations and shimmy. Also if the hub isn't spinning inline the best rotor won't help. A bent wheel will shake the car all the time, but won't likely cause brake pedal pulsations.

PS I have felt pulsations from some types of anti-lock brake systems but you said that you pulled the fuse to eliminate that. (Ford, shhh!)

 

No, this would cause a dropped pedal that would come up with each pump of the pedal. It also would actually cushion pulsations since air is a cushion(like air springs in the XJ8) and you would feel less of a pulsations. with fluid it is a direct transmittant of sensation or pressure, which is how hydraulics works and why air is so much not wanted in a hydraulic system. Jaguar actually has cleaning rust from rotor/hub contact surfaces in proceedures for checking runout. This is also assuming you have checked for hub freeplay, if there is any in nonservicable wheel bearings(which yours are), theyre bad, period.

 

moved the wheels from back to front no change. wheel bearings no play and they both have been replaced one has 35xxx and other about 20xxx miles. However this problem has progressed from slight to very bad over six months or so. struts replaced at 52xxx , but not the strut mounts. how can I tell the mounts are bad? This is the wife's car and I don't get a chance to drive it often. I am checking all other items suggested by the group thanks jim