How tough is the bond between the metal backing and the friction material?

Retrieve your old pads and try and get the friction material off, think you'll find it's impossible without smashing them into tiny bits!

I think it is more anxiety than any real concern, I presume that they are well bonded and a few taps to remove them from the assembly won't damage the friction material bond.

How tough is the bond between the metal backing and the friction material?

Pretty tough.

In high corrosion environments you can get "rust jacking" where expansion of corrosion on the backing plate breaks the bond, so rust can be tougher, but that wouldn't happen on new pads, and I'd guess it wasnt seen on the old ones either.

OTOH I have had brake shoe liners, which I'd expect to be basically similar, come off, though in one of the I THINK 2 cases it was contaminated by brake fluid.

Maybe they use older bonding tech.

Edited by edlithgow on 27/06/2024 at 03:07

There would still be some braking effect even if there was no padding and just metal to metal contact.

Unless the piston's pushed all the way out!

Impossible if the backplate was still there. Even if it wasn't, the piston itself would push against the disc and provide noisy, if minimal, braking effect......e.g....

www.taurusclub.com/threads/inner-brake-pad-missing...c***ing-on-rotor.234433/

There would still be some braking effect even if there was no padding and just metal to metal contact.

Unless the piston's pushed all the way out!

Impossible if the backplate was still there. Even if it wasn't, the piston itself would push against the disc and provide noisy, if minimal, braking effect......e.g....

www.taurusclub.com/threads/inner-brake-pad-missing...c***ing-on-rotor.234433/

I beg to differ. I had total brake failure when this happened. Unbeknown to me, a previous owner had the discs skimmed. I'd noticed the pads were getting low and had it in mind to replace them. On a fast journey, one of the caliper pistons came our too far and 'tipped' sideways, holding the pad gently against the disc. Not enough to notice, but enough to get so hot it boiled the brake fluid. Liquid vapour's compressible, hence no brakes. Fortunately nothing untoward happened, other than a brown trouser moment from going into a roundabout far too fast!

Not quite understanding how a piston "tipped sideways" wouldn't be a huge brake fluid leak, though that would also be expected to cause a brake failure.

I think I've had a very similar failure mode to the one you describe when my brake shoe liner came off, probably because of a wheel cylinder leaking due to corrosion caused by ancient brake fluid.

The shoe jammed behind the other one and I believe heated up the ancient brake fluid, which then boiled, failing the brakes.

Converted me to regular brake fluid changes, but I suppose it could have boiled even fresh fluid if it got hot enough.

Edited by edlithgow on 27/06/2024 at 03:04

I think I've had a very similar failure mode to the one you describe when my brake shoe liner came off, probably because of a wheel cylinder leaking due to corrosion caused by ancient brake fluid.

The shoe jammed behind the other one and I believe heated up the ancient brake fluid, which then boiled, failing the brakes.

Converted me to regular brake fluid changes, but I suppose it could have boiled even fresh fluid if it got hot enough.

Indeed so. The ancient system of brake cylinders and their pistons located inside unventilated brake drums was like having them inside a hot oven. It's hardly surprising that brake fluid boiling was such a common problem in the mid 20th century. Modern calipers hardly ever get so hot so boiling brake fluid is now virtually unknown. The anachronistic advice to change the fluid frequently to guard against a few degrees drop in the boiling point if there is minimal hygroscopy is no longer so relevant, especially as modern brake fluid reservoirs are designed to prevent atmospheric contact.

Yeh.

Well, this was a 20th century car, so the advice was contemporary and evidently applicable to it.

I'm slightly surprised to learn that there are no 21st century examples of drum brakes, but admittedly 21st century cars are of only academic (and rather morbid) interest to me.

As well as the boiling, there was very extensive corrosion, which caused the leak, that (probably) caused the heating, that caused the boiling. Without the boiling, it would still have been a very good idea to avoid the corrosion, which required both wheel cylinders replaced, a full caliper strip both sides, and should probably have involved a master cylinder strip as well, but I couldnt get a seal kit so just crossed my fingers on that, and got away with it.

With no ABS system, brake fluid replacement and flushing on this car was trivially easy, using an enema syringe, and DOT3 brake fluid was cheap, though a bit hard to find, so prevention would also have been trivial and cheap.

I dont know if more modern cars are invulnerable, but my strong impression is that they are a PITA to do much work on, so if I had one I would try and avoid having to. I imagine their more sophisticated brake systems, involving vehicle dynamic stability systems and suchlike geewhizzery, would be expensive to replace too, and maybe not very DIY compatible.

IIRC you have a 20th century car also. Good luck with it.

Edited by edlithgow on 29/06/2024 at 01:52