How does the disk brake piston retract?

bsquared

My front disk brakes were binding, one of the pistons was stuck, so I removed the calipers and used compressed air to blow the pistons out. It was kind of cruddy inside, but I didn't want to scrape and damage the seals without a rebuild kit on hand, and not wanting to score the cylinders. But I was wondering, hydraulic pressure forces the pistons out, so what allows them to retract? Or, are they supposed to just barely drag on the rotor?
Thanks,
Bsquared.

I've got a new seat now from a local upholsterer...looks great for $141.00 on the old pan. New foam and vinyl, original trim. Things are looking up since my rebuild on this 1971/2 xs2 650 began last year April!

Shannon60

they don't retract, when the pressure is released from the master they are at rest, if they were to retract it would take several "pumps"of the brake to be able to stop

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

bsquared -- they didn't have chocolate brownies in ancient Palestine. They had camel poo. . . .

jayel

the rubber seals pull them back a tiny bit bs but the not retracting will probably have more to do with the fluid in the master being dirty and blocking that little bitty hole under the resevoir tab, clean the whole system hoses too.

bsquared

jimmythetrucker wrote:

bsquared -- they didn't have chocolate brownies in ancient Palestine. They had camel poo. . . .

I guess that would explain the extra fiber....
Regarding the brakes...Mine don't seem to come totally to rest...too much chocolate and coffee. I'll have to brake down and buy a rebuild kit and clean out the system. It's comes a long way since the lines were totally clogged with crystallized brake fluid and wc pistons froze to the bores....but it's still sticky...must be the poo.
Thanks,
Bsquared.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

There is a square sectioned o-ring in the caliper that acts as the seal. It is located in a groove either on the piston or in the bore wall of the caliper. As old brake fluid dries up and starts turning into lumpy gravy, it gets down in this groove behind the o-ring and forces it out more. This causes the piston to bind up in the bore and stick. You need to remove the o-ring and thoroughly clean that build-up out of the groove to free things up again. Just cleaning all the exposed parts and areas without doing that groove is not enough.

bsquared

I put it back together, if it's still sticking, I'll get the rebuild seals and rings and go the whole route. I did notice that when I put the pads in last time, I flipped them so the wear pattern was crossed. I'm sure that didn't help matters any.
Thanks for the feedback.
Bsquared.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

I've never needed to install a rebuild kit on the several I've cleaned out. These Yamaha brakes are pretty robust. Clean everything up real good and re-assemble. If it leaks, then you'll need the rebuild kit, if not then you're good to go.

bsquared

Hey, the brakes are working, not binding, I might have a tiny air bubble yet in the lines. It seems like I should be able to lock up the front wheel, just to test it at low low speed. I might have a bit of oil smudge on the pads from dirty fingers...Things are looking up.
Thanks for your help.
It does need new lines...they are over 30 years old, they may be blowing up a bit under pressure.
Bsquared.

xsleo

spray can brake cleaner gets the pads and rotors clean. i just changed tires and got tire lube all over the rotor wholly s#it no brakes. a shot of cleaner worked wonders.

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