How much, and does it vary by type of disc brake?

thanks

gary

On Nov 11, 6:12 pm, wrote:
How much, and does it vary by type of disc brake?

thanks

gary

Most automotive types have some method built in to slightly withdraw
the pads when the peddle is released. On some they use a little play
in the disk to do that, on others, there's a shaped rubber seal on the
piston that does it. Just depends on who designed the brake system.
I know with my old VW I could coast 3/4 of a mile or more on the flat
at very low speed with the clutch in, very low drag in that system.
That had two pistons in each caliper, you had to make sure the piston
seal was in the right way or it would stick.

Stan

wrote in message
...
How much, and does it vary by type of disc brake?

thanks

gary

Hi Gary

Why do you want drag on a brake?

If a disc brake system has excessive wobble, so the pads are spread
excessively, it could be desirable to include a little "drag" so the pads
dont spread so far that it is necessary to pump the pedal. That is not
common
Some relatively slow vehicles that demand excellent braking use several
PSI on the pistons in their disc brake system to insure that the pads remain
in close proximity to the disc. The tugs that move aircraft use drag in
disc brake systems.
The original idea of disc brakes depended on the distortion of the *O*
ring in the piston to pull the piston back slightly.

Drum brake systems have a valve to keep a small pressure in their lines to
insure that the cup seals are spread against their cylinder walls.

Jerry