hi all,

first, thanks for all the advice given so far. this is the first jag i've had so its taking a bit of getting used to so please bare with me

the car had a 70k (it only has 60k on the clock but it was the next one in the service book) service last week and is booked in to have have the transmission oil changed and paramount supercharger pulley upgrade in the comming weeks.

the more i use the car the more i'm findout out about it (good and bad!)

when i first picked the car up i noticed a slight judder while braking but it settled down. i asked for this to be checked at the service and was told everything was in tolerance and good condition. the discs dont appear to be worn. i suspect they are replacements for the origonal as there is hardly a ridge on the edge of the discs.

the brake judder has returned but only happens in specific situations. normally when braking moderately from speed like comming off the motorway and slowing down on the slip road. the vibration continues down to ~30mph. however, braking from 50mph doesnt cause nearly as much vibration and is in fact, quite smooth.

i had the steering rack and linkages checked when in for service all with no reported issues.

the pads are 10% worn all round.

the car has been kept in storage for most of the past 3 years. however it has done around 1200 miles in the past 2 weeks (what can i say, i'm enjoying it!)

any suggestions as to what the cause might be?

 

Ross, I had a very similar thing with my old Mazda estate, turned out to be that the old tyres weren't quite perfectly round any more. Possibly owing to being out of balance for way too long. Weird thing was it really only showed up under braking when the slack in the ball joints allowed it to all go out of line. Two new tyres and ball joints cured the issue. Might yours be similar? Are the tyres balanced? And still round after sitting for three years?
Good luck...

 

Hi rossh had same problem with my 2002 xkr. braking at higher speeds,turned out to be the brake rotor on the front. changed them then all was well

 

hi jrb53,

did you measure the runout on the disc as I'm told mine are within tollerance.

i've got a dial gauge so was planning to measure runout (if it doesnt snow) this weekend.

 

Rossh, is the judder more noticeable under light or heavy braking? It could be the tires but they will normally give you signs of flat spots or broken cords internally even while just cruising.


The usual cause for brake judder under normal braking is a bad rotor that is either no longer true and has been previously warped under repeated heavy braking that heats it or the possibility that your pads have become glazed after sitting for some three years. If the rotors show no unusual run-out then you might get at the pads and give them the once over with some medium sandpaper and see if that doesn't help.

 

my money is on the rotors up front

 

i'll measure the runnout at the weekend. does anyone know what the correct limit for runout is?

 

hi all,

well i measured the run out on the discs and its only 0.07mm so i'm not convinced they are warped enough to cause the vibration.

the vibes are worst when breaking from high speed but also noticable at very low speed. when moving in very slow traffic and gently applying the brakes, it feels like they are pulsing on and off...

anyone got any idea what i should look for?

regards,
Ross

 

Runout and warpage of rotors is pretty much a myth on street driven cars. The judder you describe is most frequently cause by minor build up of pad material adhering to the rotor friction surface.

Any local garage will have the tools to remove it- an angle grinder and flexible abrasive pad, or you can buy a kit from 3M to do it yourself.

 

well i cleaned the discs up with emery paper and disc cleaning fluid and has changed the feel of the vibration. i think i'll try fresh pads. the car has been sat in a garage for a few years so they are maybe contaminated.

 

If you are going to change the pads you might as well change the rotors. I brought mine from brake labs in California on Ebay. cross drilled and slotted with ceramic pads for around $300 front and back. no more brake dust,and you will stop on a dime..........

 

Emery paper is nowhere near coarse enough to fully remove the deposits. 120 grit is the recommended product.

3M Roloc Brake Rotor Surface Conditioning Disc Starter Pack 1410

 

I am surprised that not one responder has mentioned the pulsation sometimes experienced caused by the ABS system. I have had this occur with other cars, but not yet with the Jag.

 

Wonder why both component and vehicle manufacturers bother to
discuss, have measuring techniques, and limits for a phenomona that
is labeled as a myth.

Even more surprising is that some people actually do the measurements
as specified and observe out of tolerance conditions.

All this for a mythical phenomona that could not possibly exist.

We should all just throw out our dial indicators and micrometers.

 

Plums..... Hmm...... Appropriate name!
There is no need to be so big headed. You are also talking utter bollox!
Discs can warp so it is quite appropriate for manufacturers to give tolerances and for those measurements to be checked even if warping is unlikely.

 

Just to add another dimension to this - I had an intermittent brake judder on my 2005 XK8 4.2 N/A for quite some time since I bought Nessie. I couldn't track it down, not specific to any road condition, speed or driving style, had wheel balance done, had rotors and pads changed, brake callipers checked (Brembo), track-rod ends replaced, wheel nut torques checked (20" rims apparently can be sensitive to this) but nothing would effect a permanent cure although some would provide a minor improvement for a short while. Nothing would restore the braking performance I enjoyed on my previous Jag, an XJR-100.

Last year I had the lower wishbones replaced with reconditioned units from Berkshire Jag as the ball-joint boots had split (now an MOT failure point). My brake judder has disappeared and I am convinced it was worn lower ball-joints which caused it. Moral of story - other components are involved in braking performance - get them checked too, especially lower ball-joints which are prone to wear even at 60K (I had Nessie at 50K and now am convinced the ball-joints were on the way out then probably due to accelerated wear caused by split boots). As a bonus, general steering and straight-line handling was much improved especially over rough surfaces.

Hope you get your problem resolved.

 

The tolerances and measurements for runout and parallelism quoted by OEMs are for post-machining purposes in every case I've seen. This ensures that a badly machined piece does not return to service.

The min. thickness dimension (not relevant here) must be checked after machining for obvious reasons and is good practice to check prior to machining to see if there is sufficent material.

There again, machining is only required in a small minority of cases.

 

I'll just let this link do the talking on brake, rotor and pad problems.


Raybestos Brake Tech School, Part One: Rotors Don't Warp | Hendon Publishing

 

Here's further info on the pad material transfer topic and additional comments on the warpage myth

-Warped- Brake Disc and Other Myths

Tech Article: Warped Brake Discs

Stop the ?Warped? Rotors Myth and Service Brakes the Right Way

 

I have brake vibration issue with my 98 XKR. Light and heavy braking are ok, always happens during normal braking. Replaced the front disks (Brembo drilled and vented) last January and it cured the problem. Car has been off the road for around 4 months, including the time taken to fix a blown cylinder head gasket, but now that it's running again the braking vibration is back. Can't possibly be the disks again, they are 14 months old and have only done around 3,000 miles. Took it to an MOT centre, stuck it on their rolling road, and the vibration is form "uneven braking on both front wheels." GUTTED! The disks I bought have a * after the part number to say they are an after market copy of the Jaguar/brembo units, are they really that bad that they only last 3,000 miles or could there be crud on the disks from the 4 month lay up? Any ideas?