This is going to sound really stupid, but if you have air or moisture in the system, would it expand when hot and push the pistons out slightly?
Just a stupid thought.

 

Thanks Mark, appreciate the input.
Looks like I may need to go down the route of checking out the hydraulics system too. I did get a brake fluid change around 8 months ago iirc, but the problem was there before then and since.

Cheers
Jim

 

Then its definatley not fuel related. You have ruled that out. Move on to the next possibility.

 

Well called in to see Dave re this issue, a cross between nervous and almost excited, been chasing this down for a while now!!

I went through everything that had been done again and vented my frustration as Dave got the car jacked up and started to remove the drivers side wheel. This was after a brief test drive so he could experience it for himself of course.

As the wheel came off, he checked various bushings etc and then also checked for hub run out, removing the disc after checking that too....... he commented on how well it looked and that everything seemed in really good order.

Discs, calipers and caliper carriers were all removed too and everything was checked, wire brushed and or cleaned. He eventually got around to removing the piston with a quick shot of compressed air it popped out really easily. He checked the slider pins and they were all A ok, the piston looked great as did the seals and everything else.

Strange to say but NOT GOOD......I was hoping for the exact opposite!!

All cleaned, wire brushed, lubricated, new seals and piston, sliders etc etc and all buttoned back up, wheel on....done, now for the passenger side.

Started the same process on the passenger side and everything was duplicated and everything was bang on the same, no issues, nothing to show for the nights work, then.......

As he got the caliper off and was setting about removing the piston in exactly the same way with compressed air, pffff.......nothing!
The piston on the drivers side just popped right out very easily?

Tried again, and again and then, bam, out she came.
There you go he says, there's your problem!!!



The piston was rusted around the rim and had been sticking, not retracting as easily as it should have been, probably stuck on, causing the disc to heat up and or warping causing the brake judder he reckons, see attached pics.....

As before all replaced, wire brushed, cleaned, lubricated and put back together
Went for a test drive and yes, the issue still seems to remain, albeit less aggressive. He reckons that the disc will be warped / have run out on the internal face and once replaced should be all good.

This could be music to my ears!!!
I'll be checking with Prestige and Pagid tomorrow ( They promised another set of discs / pads under warranty ) and hope to get them fitted ASAP and get an alignment done, possibly wheels double checked again for balance and see if this is finally sorted.
Fingers crossed, but could be the best £100 I've spent in a long time

I'll report back obviously
Jim

 

Into Prestige in the morning for new discs and pads again, at last...
Hopefully this should now resolve this issue, but only time will tell ( approx. 6-8 weeks usually does it )


The plan is to get the car checked for 4 wheel alignment too, as well as all 4 wheels checked for balance and redone as may be required.....leaving nothing to chance
Jim

 

Horrors. Don't tell the disc/pad suppliers as they could reasonably refuse to replace the parts!

 

At last! fingers crossed

This is incredible.
Solved now, thanks to the insistance of a good pro.

Is that uncommon? Responsibility of Jaguar or of the brake system supplier?

 

Just age I guess. Things age and fail...

I suppose we all ought to inspect the pistons... Hands up who has? LOL

 

Well, in at my Indy today to look at these issues again.
Pagid have once again, stepped up to the plate, even though I guess I theory / practice they could've walked away by now!
They supplied another free set of discs and pads, see pic.....



These were fitted by my Indy and then I asked for a 4 wheel alignment, this was done too, all for no charge!!

Happy bunny to say the least.
Of course as it stands at the moment the braking juddering issue is resolved, only time will tell if the piston was indeed the cause, I should know in about 6-8 weeks I guess.

Afterwards even though I was confident that the wheels were properly balanced I had the fronts done again.
All good for now

Jim

 

Jim, this is why I say, caliper rebuild should be an integral part of any complete brake service, and most overlooked.

 

I do every service interval. The proof is in the inspection.

 

What percent of those do you find a bad piston?

 

The question to ask is what causes that type of corrosion, and how long was it left unattended. No braking system should be allowed to get to that point, and when you just slap pads on, without bi-yearly fluid flush, and caliper square seal replacement during the brake job, (as well as other rubber items) this is the result. It's why I say, no brake job should be done half way. It is one of the most ignored, and most needed items of any complete brake job. Your life, and the life of others rely solely on this system to stop nearly 2 tons of rolling metal.

 

You did not answer JagV8's simple but relevant question ?


" Originally Posted by JagV8
What percent of those do you find a bad piston? "

" The question to ask is what causes that type of corrosion, and how long was it left unattended. No braking system should be allowed to get to that point, and when you just slap pads on, without bi-yearly fluid flush, and caliper square seal replacement during the brake job, (as well as other rubber items) this is the result. It's why I say, no brake job should be done half way. It is one of the most ignored, and most needed items of any complete brake job. Your life, and the life of others rely solely on this system to stop nearly 2 tons of rolling metal. "

 

Hi Mastersid, what question was that?
Did I miss something, was it directed at me?
Please advise....


Thanks
Jim

 

Hello Jim , no , not directed to you , the question was that was asked in post #32
in response to post #31 .

Sid .

 

Pistons do not just "go bad". The corrosive affect of fluid that hasn't been proper maintained, and the failure of rubber seals that have not been properly replaced over the life of the vehicle, (and this is part of any complete brake job) leads to this type of part failure. Most vehicles by the 100,000 mile mark should have had caliper rebuilds at least 2~3 times, (every pad change) and flushed fluid 4 or more times.

I can't stress strongly enough, that if you feel that a brake job consists of replacing pads, and maybe the rotor, then you are only doing half a brake job. Both fluid and calipers need regular maintenance as well, and Jaguar certainly has brake fluid replacement every 2 years as part of the regular scheduled service requirements. But even a brake bleed will not get all of the corrosive fluid out of the caliper itself, only disassembly and cleaning will do that.

So to answer your question bluntly, if the proper maintenance at time of brake job is done, (20~30k miles when pads are replaced) very seldom if never. If improper or half done brake jobs are performed, (not performing caliper rebuild service) by 100k mile, you are more than likely to find corroded piston surfaces.

 

David , thanks for your reply

Take a closer look at Jim's piston , from where the seal sits to the bottom end of the piston there is NO " corrosive affect of fluid ".

What can be seen is the failure of the outer dust boot which has caused the oxidization at the top end of the piston .

I also think it's a bit premature to suggest that the piston is at fault given that Jim has said it will take about 6-8 weeks to find out .

And by the way , you still have not answered JagV8's question ?

Have a good day David ,

Sid

 

Sid, I used to work for an automaker in the Parts and Service Division for nearly a decade. I'm a certified ASE Master tech. I've seen 10's of thousands of vehicles, both under and out of warrantee. I've been repairing autos since the 70's. And I did answer the question. You may not just like the answer. Fluid passing the square cut seal, (which is where the corrosion begins, at the point of where the square cut seal is at its early travel) and being trapped between that seal and the dust boot, combined with just a little moisture will corrode the piston as seen above. Had the caliper been serviced properly, both the square cut seal, and the outer boot would have been replaced, and if done correctly the bore cleaned of rust and debris, piston cleaned and corrosive fluid removed. Pitting behind that point would demonstrate high water contamination behind the piston inside the bore. Rust inside the bore is also a condition of high water saturation of the fluid.

I'll say it again, any time you replace pads, and do not exchange both fluid and rebuild the calipers, you have only done half a brake job. Preventive maintenance is what keeps issues like this, from becoming an issue. You should know this if you are in this industry, and properly trained.

 

David , I'll let the Forum members decide whether they feel the need or the expense to dismantle and clean their calipers at every " service interval " .

The question you seem to be avoiding is really quite simple ,

After you have inspected your pistons at every service interval , what percentage of those pistons were bad ? , given that your XJ8 is now 12 years old .

Sid