Disc Brakes

Lots of WD40 and perhaps an air hose in the bleed hole.

Or tap it with a hammer against a block of wood on the high side

Usually the g clamp into the centre and tap it with the pressure on after applying wd40 after taking the rubber seal off

Gday,

Id take your calliper into a brake specialist.


Cheers

Michael, Have just done the same thing. You have to scrape around the edge of the piston with a screw driver or knife to get off the crud. Then give it a good spray with WD40 or equivalent. Give the "G" another go. Make sure the cap of the brake reservoir is off. Otherwise you are attempting to push against the system! I know what will win.
Good luck

Michael46

How important is stopping your car ,in your list of priorities in life?Mate, take it to a specialist.Its a bit different to mucking around with the carby on a red motor (If it don't work ,it don't matter )

Cheers
Giffo

Michael
If its stuck its either wedged in crooked or it's seized. If seized you want it out to replace the seals and clean the rust out of the callipers. If jammed see if you can pick which angle the piston is sitting at and apply your clamp gently to straighten it. In either case you are going to have to take the piston out to assess any damage. Apply some gentle heat to the calliper to expand it either boiling water or low blow torch (don't put it directly on the calliper) Clamp the other calliper and apply brake pressure to see if the piston will come out.

good luck

Hi Michael
1st,try, release the bleed screw and then try to move it back with a clamp.

2nd , Try with a assistant ,get them to pump the brake pedal in a small amount while you watch the piston to see if it moves out
it will only need to move about 3mm ( not all the way out )to help free it up and then try to push it back.

3rd, it is possibly seized solid rusty etc,pump the brake pedal until you pump out the piston and fit a new seal kit and piston if the piston is rusted.

4th what Hairy said.

Michael if it's jammed it is likely water has caused it to seize in there, therefore you'll most likely have some pitting on the walls of the cylinder which is extremely difficult to remove with a hone.

Consequently, it will be very difficult to get a seal that will not eventually leak and cause brake failure.

Personally, I would bother trying to fix it. I'd replace. Speaking from experience.

"What do you do when one of the brake calliper pistons will not retract into the calliper"

Michael.

The answer to that question is simple: you take it out. If it won't slide back in freely then it will almost certainly stick again. It may not happen the first few times you use the brakes but it wont be long.

The usual way to get it out is with compressed air. You always put a piece of wood into the calliper first so the piston does not come flying right out at blinding speed when it lets go.

Once you get it out, it is usually just a matter of cleaning the piston and calliper and reassembling them with a new seal lubricated with either brake fluid or rubber grease. I overhauled countless callipers at work years ago and I can not remember ever having to replace a calliper and I very rarely had to replace a piston. Corrosion in the calliper is not very common and it does not cause any problems anyway because the seal is stationary in it. The piston slides through the seal instead of the seal sliding in the bore of the calliper like it does in wheel cylinders or master cylinders. As long as the piston is clean, smooth and shiny, then it is ok. Clean it up with 1500 to 2000 wet or dry paper.

Don't forget to replace the copper washers on the hoses. If you can't get new ones then the usual thing is to soften them before using them again by heating them until they are red and dropping them into water.

If you don't have the facilities to do this, then take it to a brake specialists. There is not much labour involved in overhauling callipers once they have been taken off the car so it should not be expensive.

While you are at it, do both sides because they will both be in much the same condition. If the car is getting on a bit in both age and mileage, then you will probably find the rest of the hydraulic system also needs attention.

Brian

if the caliper is aluminium you can also soak the area in vinegar (don't laugh). aluminium is alkaline ( I think I've got it the right way round) and vinegar is acid so it neutrallises the aluminium oxide build up. we used to do it in UK on seized brakes.