THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

The stiction terminology actually comes out of the shock absorber industry & especially the stick slip action they frequently battle on the front forks of motorcycles.

Sounds as if you have a good plan.

Glyn
Thanks for the detailed reply. From where I'm at now, i think I'll just order up a new set of front rotors and probably Coopercraft calipers. Then I should be good to go for a while.

Again - great to hear from an expert on friction/stiction
Roger Young

There were aftermarket shims available at one time that you could place behind the pad backing plate. Doubt you would find any today. They were a jury rig for not understanding that brake squeal was caused by resonance in the disc itself (high-frequency vibrations of the disc). Rectified in disc manufacture initially by including a cast iron damping ring in the disc itself at it's perimeter. Today by materials change to move the point of resonance outside the critical frequency.

Dunlop scrapped their efforts to stop caliper over return as they did not really work. Your right rear disc might be suffering from chronic caliper over return on one side or a seized piston. I had a single caliper side over returning on the rear that I had to rectify after educating my restorer.

Any air blown into a braking system should be dry as in any good paint shop. Apart from other painting issues with moisture present, paints containing isocyanate do not harden properly if moisture is present.

You could have your front calipers stainless lined then they would be correctly bore sized for standard seal kits as I did. Your choice vs new.

Good luck!

I just took a look at Glyn's link and found it interesting and enlightening - I also learned what a tribologist is. The shop didn't have any spacers behind the pads - the design of the Dunlop calipers doesn't seem to allow for any. The post rising from the center of the piston is the fitting for the clip on the back of the pad. I can't see how any spacer can be placed.

Also blowing air into the caliper as referred to in the link - doesn't that put moisture into the works?

Thanks for the multiple replies. I did refill with DOT 3/4 but they were leaking before that and supposedly the shop used DOT 4. I also noticed that the right disk had zero wear on the inner side - literally pristine - while the outer surface was slightly groved. I think the inner wasn't pressing at all. I think I am stuck with getting new front calipers.

You got lucky with your caliper seal material compatibility. Many elastomers can't tolerate it and it's very difficult to know what rubbers you are getting. I'm an oilco tribologist. Seen many leaky seals. Because you got away with it on one car does not make it universally acceptable.

For what it's worth I've been running DOT5 silicone brake fluid in my S for decades with no adverse affects. But good info on not pushing the caliper pistons in any farther than necessary but my pads seem to last almost forever given the relatively low mileage the car gets and not being an automatic.

The standard elastomer caliper seals are designed to run on straight DOT 4 Brake Fluid. Did you run some exotic or silicone brake fluid in the system?

This is most unusual unless the proper fluid is not used.

I'm using standard Dunlop calipers on my S type but have had everything stainless steel lined as it is a low use car.

Your noisy caliper probably just needed a pad shim. Might have been over returning slightly. You should never push the pistons back in the caliper any more than is required to insert pads or over return can occur.

http://www.jagstyperegister.com/forum_n ... turn#p1340

I have written about this extensively at MBWorld.

I had the brake calipers on my 65 S-type rebuilt by a vintage Jag specialist (Kings Cross Automotive in Vancouver Washington, US) about a year ago. They worked fine, except for an unusual squeeking from the rt front when NOT applying the brakes. Interestingly, the squeek went away with even light braking. Other than being annoying, the car stopped well without pulling left or right. The car was sitting for the winter, but after a couple of months sitting, both front brake calipers were dripping fluid and the reservoir was empty. I ordered up new seals and pads and started to just redo the job, anticipating I'd find a broken piston or seals, or both. Anyway, I disassembled the calipers and all looks normal on both sides. The fluid was definitely coming from the calipers. I'm starting to think I should have just refilled the fluid, bleed the brakes and not done anything. Does anyone have any thoughts? (I'm just getting ready to put everything back together again). At the other extreme, I'm considering upgrading the calipers.