stuck pistons

[guitarcarrot]

simple question:

Can a few sticky/stuck pistons cause brake pulsation?

[richr]

thats usually warped discs

[guitarcarrot]

yeah ive heard alot about that, but ive checked runout and it is half the service limit...

then i saw this: http://www.ebcbrakes.com/automotive/bra ... tion.shtml

so i checked the thickness at random spots with a micrometer precise to a 1,000th of an inch and all identical readings,

ive cleaned the discs with brake disc cleaner still i could no longer bare the squeaking, still to no avail

im loathed to try new pads as i really doubt thats the problem,

but i have two very sticky pistons in each caliper which makes me wonder

ive had to take my mirrors off because they were vibrating and putting hairline cracks in the paint around their mounts,

[RedexRobB]

Well if you can free up the pistons that can only help things i would have thought, weather thats the problem or not is another thing but i would free them up if i were you.

Did you check the runout across the surface of the disc rather than at one point?

[guitarcarrot]

Yeah ill do that then, whats the protocol with seals? If they look tatty get new ones?

[stonemonkey]

check visually for any wear/cracking/perishing and replace if in doubt. The dust seals on mine were sticking after having not been used for 8 months. I used a g-clamp to push the pistons in, reblead the system and it worked a treat!

[pizzaboy]

caliper pistons do not stick because of damaged or worn seals they stick because of corrosion in the groove where the seal is located.
The seals also play a role in moving the piston back from the pad/disc.

New seals wont help unless the groove in the caliper body is cleaned

and sticking pistons lead to poor braking efficiency and excessive pad/disc wear and over heating of disc which could lead to warping