what pulls brake pads off the rotor?

[peanotation]

after you press on the brake, and the caliper has released it's "grasp", what pulls the pads off the rotor? i know they only move thousandths of an inch, but even if the pads were barely touching the rotor i'd imagine that's a considerable amount of friction whilst driving, and thus more heat.

 

[Defiant]

You're not going to like this.
It's the flexing of the rubber seals on the piston.
I know, I didn't like the sound of it when I first heard about it, either. It'll never work. Luckily, the brakes don't seem to realize this.

 

[Ho0ked]

You're not going to like this.
It's the flexing of the rubber seals on the piston.
I know, I didn't like the sound of it when I first heard about it, either. It'll never work. Luckily, the brakes don't seem to realize this.

Shity but true, those little rubbers do work well enough, hence the need to lube the slide pins well

Side note, they also help keep the grease in the pin and the road debris out, but worst case some springs could always be utilized but shouldn't be needed


Hmmm PS. just relize your talking about the piston seals I believe? well yea i'd say those and the slide pin boots provide the negative pressure.

 

[Defiant]

Yeah, it's the piston seals. But it'll never work. The other thing is slop in the wheel bearing that lets the discs themselves knock the pads back. Hardly sounds any better.

 

[tkelly27]

Or the slight wearing of pad material until it no longer touches. Once you've cut a piece on the lathe it stops touching the bit if you don't force it in any further.

 

[D_Eclipse9916]

Yeah, it's the piston seals. But it'll never work. The other thing is slop in the wheel bearing that lets the discs themselves knock the pads back. Hardly sounds any better.

You know I never really thought about it, but I thought it was "pad knockback" and the movement and friction of the discs that pushed them back.

I dont see how piston seals would do it...considering Wilwood calipers dont use rubber piston seals.....

This is a question, please explain as I actually dont know

 

[this_tsi_8urV8]

I know old thread, but I thought it was the pressure from the brake fluid itself pushing back the calipers piston.

 

[TheMadCheshire]

Its the piston seal. When the piston is pressed outward the seal is twisted upward since it is a square cut seal. When pressure is off the piston the seal naturally wants to be straight so it pulls the piston back.


Some companies(espcially toyota) will used little pad springs that are shaped like a "V" and grab each pad on the side of the metal backing using a machined hole. The "V" will push the pad back and can be a pain to reinstall new pads with new hardware because the moment you let go of the pads to slip the caliper on, the pads slip outwards and you got to do it all over again. Ugh.

 

[deth2u]

Its the piston seal. When the piston is pressed outward the seal is twisted upward since it is a square cut seal. When pressure is off the piston the seal naturally wants to be straight so it pulls the piston back.


Some companies(espcially toyota) will used little pad springs that are shaped like a "V" and grab each pad on the side of the metal backing using a machined hole. The "V" will push the pad back and can be a pain to reinstall new pads with new hardware because the moment you let go of the pads to slip the caliper on, the pads slip outwards and you got to do it all over again. Ugh.

If you think that's bad, try loading an older sliding Porsche caliper.

I nearly went insane trying to put the mother ####er back in

 

[MIdsm]

You know I never really thought about it, but I thought it was "pad knockback" and the movement and friction of the discs that pushed them back.

I dont see how piston seals would do it...considering Wilwood calipers dont use rubber piston seals.....

This is a question, please explain as I actually dont know

There is a difference between rubber piston seals that all calipers have and the dust seals/boots that street calipers ought to have and many racing calipers don't.

The piston seals keep the brake fluid behind the caper pistons and keep the system sealed. The dust seals keep the dust away from the piston bores and piston seals. Dirt can damage piston seals and lead to brake fluid leaks and total braking failure.

Race calipers get rebuild on a regular basis and piston seals get replaced. The dust seals would melt due to hight temperature encountered during repeated heavy breaking and may cause the pistons to stick.

Wilwood calipers, as a general rule, don't have dust seals as they are race calipers.

The auto manufacturers have to warranty their vehicles for long periods of time. Many car owners barely have the oil changed and would not be willing to rebuild the calipers every couple of months. With the dust seals installed the piston seals last for years and many tens of thousands of miles.

Please pardon my ramblings.

 

[Project2G]

The brake caliper fits over the rotor like a clamp. Inside each caliper is
a pair of metal plates bonded with friction material -- these are called brake pads. The outboard brake pads are on the outside of the rotors (toward the curb) and the inboard brake pads on the inside (toward the vehicle). When you step on the brake, brake fluid from the master cylinder creates hydraulic pressure on one or more pistons in the brake caliper, forcing the pads against the rotor. The brake pads have high-friction surfaces and serve to slow the rotor down or even bring it to a complete halt. When the rotor slows or stops, so does the wheel, because they're attached to one another.

My old RS used drum brakes, where the motion of the wheels is slowed by friction between a rotating drum and brake shoes mounted inside the drum. This friction caused heat and gases to build up inside the drum, which often resulted in a loss of braking power known as brake fade. Because the brake pads in disc brake systems are external to the disc rather than contained within a drum, they are more easily ventilated and heat doesn't tend to build up quite as fast. For this reason, drum brakes have been largely replaced in modern vehicles by disc brakes.