Rear brake Caliper piston removal

[ghia70]

H, any tips on removing the pistons from the Calipers, be soaked in release fluid, tried air to push them out, don't seem to be rusted in and from previous recipes were fully rebuilt about 10 years ago. any advice appreciated. they are ATE callipers.

Thanks

Danny

[Lightweight_911]

Are the calipers still on the car or off ?

[davep]

I always work on the calipers either on the car or on my bench setup with spare pedal cluster & master cylinder. Use hydraulic pressure to force them out one at a time. Using air just sets you up for cannon shots; dangerous & damaging.

[RichardBTek]

Best way would be to connect them back up to a master cylinder and pump them out if you can.

Richard

[ghia70]

Ok thanks for the replies, calliper is off at present but will connect up and try that route.

[james1432]

I overhauled my front callipers last year and came up against the same problem getting the pistons out.

What a pain!

I ended up using a grease gun method. Bought a draper grease gun which fortuitously had an attachment with the same thread diameter as the brake line nut. Pumped the grease in and out came the pistons. Clearly one will free off before the other so you have to work out a way of holding it back but it wasn't too much of a problem.

I did find myself with a particularly reluctant piston on one caliper that needed a good degree of pressure all the way through it's travel. I removed the opposing piston then placed a small piece of plastic tubing with the outside diameter matched to the bore of the cylinder (with a bit of tape for a snug fit) to block off the port. This allowed all the grease gun pressure to be applied to the remaining piston and out it came.

Once the pistons were out I made sure to blow compressed air through all the ports and cavities to get rid of any residual grease.

I admire the fact that our half-century old cars have disc brakes but, after the above, can see the advantages of modern single piston 'floating' callipers!

PS. I hear it is a very bad idea to attempt to separate/split the caliper as it's nigh on impossible get an adequate seal once they're back together.

[ghia70]

Finally removed the pistons, temporary fitted the calliper back on car and pushed the pistons out placing a bit of wood in the centre to stop firing out., got new seals etc, all cleaned up however pistons even without the rubber seals installed will not fully go back into the bores, both sides the same.
questions

Can the bores or pistons become warped ?
any other ideas on why they won't go back together ?

alternatively any recommendations on companies who can refurb the calliper

Thanks

Danny

[wildtexas]

Danny, the first thing i would be doing is measuring the pistons and bores with a calliper.

I have never experienced one out of shape but they are always a tight fit. Getting them in square and true can be a challenge. Matt

[davep]

I generally fully disassemble the calipers, but then I have all the tools and a lot of experience. This is not recommended to first timers.
The pistons I will polish with a green scrub pad and plenty of alcohol. The O-ring groove I have a dental pick to scrape inside, and finish with Q-tips.
The outer portion of the bore, from the O-ring groove, I generally use a dental scraper to remove the worst rust. Or, if sandblasted first, this area get special attention; in this case the pistons are forced all the way in to expose the outer portion. The outer portion gets the most rust, and is not a critical seal area.
The rest of the bore I like to scrub as best I can, and if disassembled I will generally hone it lightly. The outer caliper half is often the most rusted since bleeding rarely does much of a job unless that half also has it's own bleed nipple.
If the bore an piston are clean, then the piston should slide in and out with relative ease when the O-ring is not installed. I always use ATE brake cylinder paste (designed for internal use) to lube the parts. With the O-ring in place, the piston should be able to be pressed in by hand with a little effort. When doing this on front calipers I always use the angle tool to ensure the piston cutout is set to the correct angle.

[ghia70]

thanks for the feedback, all cleaned up bored and pistons cleaned, assembling without the seals in the first instance, pistons will only go half way, seems they will not go past where the seal grove is. Could the groove been causing a vacuum or resistance to the pistons going all the way back. all nipples, etc removed so the pistons should slide all the way back. when applying pressure i can feel a resistance. thoughts ?

Thanks

Danny

[ghia70]

Hi, Decided in the end to send the calliper away to be refurbished as had an issue with one of the pistons. I used Classicar Automotive, great job, total refurbish, fast turnaround (1 week) and great people to deal with. worked out approx £100 for the rear calliper, highly recommended
sales@classicbrake.co.uk.