Brake Judder '99 XJr

[HaylingJag]

Looking for some advise here Men,

I changed the discs and pads all round about 4000 miles ago and all went well until the Silverstone Sunday Service (back when ever that was) I done the track taster and came off after 20 minutes due to excessive judder on the front near side. Once cool, and under 'normal' driving conditions on the way home, everything returned to normal.
Anyway, first real serious drive out this morning with the South Coast members has re-introduced the problem and it is really quite scary. It only seems to happen when heavy demands are made on the brakes.
It has just gone through an MoT and nothing was reported, though I doubt they took it on a 100 mile high speed hoon prior to testing!!!
Im thinking loose or buggered calliper but if anyone else has encountered this I would welcome your diagnosis

Cheers
Darren

[Jaguar steve]

How do you know it's on the nearside and how does it manifest?

[HaylingJag]

Hello Steve,

i know its the front nearside due to the vibration and wobble of the steering pulling me that way, almost like the brake disc is violently warped, though its not! It only happens when under extreme conditions ie track days or heavy hoonage, under normal driving conditions theres absolutely no symptoms,

cheers
D

[Jaguar steve]

I suspect it's probably not warped discs then - that'll manifest everytime you brake either hard or very gently and once warped dics stay that way in varying degrees so you'll have the symptoms constantly.

What you may have is either a weak shock absorber, broken drop link from the wishbone to the anti roll bar or a failing suspension bush or ball joint - something that's dislocating or failing under hard loading but still working under normal conditions. I'd have a very carefull look at the tyres too and see if swapping front to rear makes any difference. You may have some internal tyre damage that could give similar symptoms. Or it could just be some scrote has tried to nick one of your wheels and left the nuts loose.

Try swapping wheels front to back first and whilst they are off have a carefull look at the front suspension. Do both sides at the same time so you can compare like for like. You're looking for any signs of slack, bright spots caused by components contacting or missing bolts or broken bits. Any signs of loose or mishapen rubber in the bushes or rust staining around ball joint dust shields may be a clue too. Check the caliper bracket bolts are tight and the caliper is not loose in the bracket and the pads are not worn unevenly or badly. It's possibl;e you may have a sticky or partially siezed caliper. Make sure the wheel nuts are torqued up to 70 ft/lb.

With the wheels back on twist at the 9 and 3 o clock positions and again at the 12 and 6 o clock positions. Put a long piece of 4x2 or a scaffold pole under the wheel and gently lift the wheel up. If you feel initial slack then resistance doing this then that's a clue something is worn.

Edited by Jaguar steve on Monday 23 September 09:04

[XJ Flyer]

I'm only familiar with the earlier XJ set up but the same probably applies.If you're not sure of the condition and exact age of all of the suspension and steering components it's best to just rebuild it all,preferably using genuine Jaguar parts,as a matter of course treating every part as consumable item just like brake pads.It's the best way of having a car that always drives like new and minimising the issues of having to solve the needle in a haystack situation of failing components anywhere in the chain.What did surprise me was looking at the drawings the front discs on the later cars don't seem to be bolted to the hubs seperately to the wheels and just seem to rely on the wheels to clamp them like the rear discs on the outboard brakes cars.

Edited by XJ Flyer on Monday 23 September 16:48

Edited by XJ Flyer on Monday 23 September 16:57

[aide]

Do you have the front cooling ducts installed?

[SkepticSteve]

I have had this on my STR, I replaced the front disks with EBC slotted top of the range jobies.

But it came back again, so I went to my MOT man and on the nearside front on the brake machine you could see the pulsing of a warped disk.

I have just replaced the disks again with standard pattern and REALLY bedded them in gently, juddering and stearing wheel wobble gone.

I suspect that the disks are cracking under extreame heating.
The EBC ones should not have done that, but when cold they were perfect and only started juddering when hot.

So far the new disks are OK, but still bedding them in by using harder and harder.
One thing I have stopped doing, is holding the brakes on, I alway knock it out of gear now and release the foot brake to allow the disk to cool evenly.

One thing the MOT man said I have never heard before, was wheel bolts being done up too tighly can cause disks to warp??

[HaylingJag]

reading through, you guys might have a point. I had the pads and discs fitted the day before Silverstone. Obviously the cross country 120 mile hoon wasn't enough to bed them in!
Cooling ducts is the other option to look at.Ill havea crawl under there to make sure this side hasnt let go

cheers men
d

[LoudV8]

Another problem that I've had with the Brembo calipers is the stainless steel skid plates on the caliper that the pads rub on.

A bit of corrosion under the plates can misplace them a bit which causes the pad to jam slightly when the brakes are released, which then results in judder next time the brakes are applied.

As I couldn't get the plates out to clean up the corrosion (they're held in with tiny allen bolts), I skimmed the ends of the metal pad backing so they sat free in the caliper.

A bit of a bodge really but time was pressing.

[pikeyboy]

The old plate lift problem.....porsches have had this issue for years. Cheap skates grind the pads other wise a world off hurt trying to get the screws out that secure the steel plates in the caliper follows.