My colleague at work ran into an unexpected result when he tried to push the
piston into the caliper on the rear disc brakes. The c-clamp method that
worked great on the front calipers failed miserably on the back set.
My research on the Internet showed that the pistons on these type brakes
must be rotated while they are being pushed in, and there is a special tool
for the job.
My question is why do the pistons have to be rotated? What
physical/mechanical feature makes this necessary?
Harry, imagine that the back side of the piston is like a very
large nut with coarse threads, and the adjusting shaft is like
a very large bolt that threads into the piston. Basically, you
are screwing the piston back onto this large bolt.
you hit the nail on the head. it's mechanically retracting...
when the parking break is activated, the lever rotates the piston
mechanically like a screw (bypassing the hydrolics).
the rear brakes uses both mechanical and hydrolic systems, therefore it is
unwound to move it out for replacing the calipers/rotors. when finished,
just use the hydrolics to push it back in (main brake pedal).
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