about 4 months ago i bought new discs and pads for front of xkr sc,4 weeks ago steering shook when braking slightly@90 mph.The man that sold me the pads and discs and he tells me that its the bembro calipers pistons sticking.What i want to know is,is there a kit which you can mend them with or do i have to get new calipers,and if so where is the best place to get them.thank you in advance.......dodger

 

The pistons in the calipers can sometimes rust and not slide smoothly when pressing the brake pedal. Maybe they just need taking apart, cleaning, greasing and re-assembling

 

BREMBO - if only the performance increase matched the price hike over standard calipers!

I was starting to get concerned at the surface corrosion of the Brembo Caliper bodies on my 2005 XK8 4.2-S:



Aluminium and steel is never a good combination. The brake pads sit on four steel slippers which are screwed to the aluminium caliper body. The corrosion had started at this connection point on all four of my calipers. It was starting to make the pads bind and I had to strip them down and clean off the corroded metal to recover the correct gap.

Provided your caliper bodies are OK, seal kits are available. Expensive from Jaguar but less from aftermarket suppliers.

If the pistons are corroded, having stainless steel ones made is not too costly and an improvement on OE.

Graham

 

A shake or vibration in the sterring wheel is usually indicative of a warped rotor. A sticking piston would usually ether pull to one side or pull when braking lightly and straighten up when firmer pressure is applied.

 

i am getting both of these symptoms and the supplier says its because heat is occurring because of warped discs and the pads are rubbing the discs which is caused by sticky pistons

 

I had pretty much the same issue as you did - I replaced my front discs and pads (EBC pads, some cheap discs), then after a month or two - I started getting a bad vibration when braking. Couldn't resolve it myself, so I took the car to a mechanic, who had the discs on a lathe. Apparently they ****ed something up on the lathe, and they broke one disc. He then gave me a new set of original Brembo rotors on his cost. No problem since.

What brand/quality discs did you put in there?

 

Did the man who sold you the discs and pads come to this conclusion by actually examining and testing the brakes or did he hold a seance?

If you fitted the discs and pads yourself, you have the knowledge and expertise to verify this opinion before spending money. The only additional piece of equipment you may need to purchase is a clock (dial) gauge to check for warping. The maximum runout quoted in JTIS is 1.0 mm on both front and rear discs (Brembo and standard). A lot of cheap import Chinese discs fail this standard.

Caliper pistons typically move very little in use and never retract fully into the caliper bores as the pads wear. If they are just pushed fully back when new pads are fitted, it is not uncommon to find them subsequently sticking at first.

I always ensure the pistons move freely by:

1. remove the old pads
2. fully retract the pistons
3. refit the old pads
4. pump the brake until the pads are in contact with the discs again
5. remove the old pads again
6. fully retract the pistons

With Brembo calipers, you should be able to do (6) by hand with no excessive force required.

Repeat as necessary to ensure free piston movement (all of them) before finally fitting the new pads. Ensure the pads don't bind on the steel slippers of the Brembo caliper. The backing plates on some aftermarket pads aren't machined to the same tolerance as OE Brembo and may need some attention with a rasp.

I also do a fluid flush at pad change but some consider that OTT!

Graham

 

discs cost £135 pair and my mech fitted them

 

At that price, they will be aftermarket discs. Jaguar JLM21749/Front and JLM21748/Rear Brembo Discs are RRP £551.62 a pair in the UK.

The only aftermarket supplier of discounted OE Jaguar discs I've found in the UK is xk8parts.com at £451.10 Front or Rear a pair.

Graham