URGENT! rear brake piston won't return

[Bishbosh1999]

While fixing a puncture on my rear tyre I accidentally pushed the rear brake lever while the wheel was off and am now having trouble opening the pads back out to fit my brake disc into. Do I have to de pressurise the brake or something?
Any help is urgently appreciated as my bike is my only means of transport.
____________________
Rieju MRT (50cc) (sold) - Yamaha WR125R

[DJP]

Hopefully you haven't pushed the piston past the point of no return (although that's not likely).

You need a set of piston spreaders or, failing that, to rig up some sort of G-Clamp to push the pistons back in.

You could use water pump pliers if you have some (put some card between the caliper and the tool to avoid marking the paint).

It may be easier to push the pistons in if you slacken off the bleed nipple (although then you'll need to top up the brake fluid afterwards).
____________________
Suzuki Bandit 1250
https://deejayp999.atwebpages.com/index.html
That's http not https

[Bru]

Bodge fix is to drive a wedge in between the pads to force them apart, which basically pushes the piston back into the caliper. Use a strong screwdriver as a wedge against the pads, or the caliper body, while taking care not to gouge or seriously damage pads, caliper, etc.

If the caliper is off, then use a G-clamp to push the piston back in, by putting the caliper body inside the clamp.

Or, use a small bearing puller, but with the legs off and the body of the puller in the gap between the piston and caliper body; screwing the threaded part of the puller in, will drive the threaded bar into the piston to push it back into the caliper body.

All of these suggestions are based on you having a sliding caliper, rather than an opposed-piston type.

[kramdra]

If piston is clean, it should push back in easily with thumb pressure. You could use a G clamp being careful not to mark piston, but excessive force indicates it needs to be stripped and cleaned.

Recommend you take pad retaining pin out, remove the pad, clean the piston. It will not go in easily if its coated in brake dust, also wont do seals any good.

[Bru]

That's a very good point about the cleaning. Do what kramdra suggested.

[salem1987]

if all else fails i bet the dust seal round the piston is caked with road grime and jamming things up.

Another Bodgers fix:
pump the brake till the piston falls out (it will be messy)
remove dust seal
clean inside calliper and piston
lube it all with brake fluid
itll slide straight in!
bleed brake
(no dust seal will reduce life of the oil seal dramatically, but in an emergency...)

Proper fix:
Pump piston out
remove dust seal and oil seal
throughly clean the inside of calliper
replace both seals with new ones
and refit with a nice shiny clean piston
bleed brake