Removing Stuck Brake Caliper Pistons

[4129R]

This thread is as much for my own help as anyone else.

After bleeding my brakes during a complete rebuild, my front discs were locked solid. The pistons would not go back into the calipers.

I bought a Triumph Spitfire caliper rebuild kit off eBay £40ish), and started the process. This is how I did it, one caliper at a time.

Remove brake pads. Pump footbrake to push the pistons right up to the disc. Remove caliper. Pump footbrake until 1 piston is free from the caliper.

Disconnect brake hose from caliper, put caliper in vice, change bleed valve (new one is 10mm not 7/16), undo 4 x 1/2" bolts, drain fluid from half with free piston. Clean caliper with kitchen towel and a rotary wire brush, remove rubber seal with Stanley knife, clean groove thoroughly, fit new rubber ring seal, put brake fluid around new piston, push piston into caliper using vice.

Reassemble caliper with new O ring between two halves. Re-attach brake line. Put brake pad in new piston side of caliper. Hold brake pad in caliper with two large ring spanners where the dis would be, so the old piston can be pushed out with the new piston stationary, with caliper on upturned plastic bucket. Pump foot brake 25+ times to push 2nd piston out of caliper. Undo brake hose.

Put caliper in vice, undo 4 x 1/2" bolts, repeat clean and fitting new rubber seal and piston as before.

Refit caliper, loosen brake pipe to put top bolt in, remember to fit hose bracket with 2 caliper bolts. Use large screwdriver to prise inside piston back into caliper. Fit  inside pad with backing shim, pad pins fit from the inside of the caliper to get P clip into pin holes in pins. Prise 2nd piston into caliper, repeat pad fitting, tighten hoses and all bolts. Bleed brakes.

These 4 pistons were stuck solid but hydraulic pressure was enough to push them out. The fluid in the calipers behind the pistons was horrible, black and full of rubbish. The two halves of the calipers needed a lot of cleaning to get them back to clean bare metal so the piston would move freely. 

[jbcollier]

Normally we don't separate the caliper halves.  Most kits do not include the seal between the two halves.  You CANNOT use an off-the-shelf o-ring.  It's a special square cut seal.  Get the right one and have it to hand BEFORE you split the halves.  These days, parts supplies are getting thin on the ground and you don't want your car off the road waiting for a stupid o-ring.

If you suspect a sticking/frozen piston.  Use hydraulic pressure to move it out as above, soak it with WD40 and then use Big-F%#$ing pliers to push it back in.  Hydraulic pressure back out, repeat until it's free-ish. Remove the caliper and you should be able to pull the pistons out using pliers -- I use compressed air but you have to be VERY careful.  And, now you don't have to split the halves.

Examine the pistons very carefully.  Any pitting or corrosion damage and they are toast.  Fit replacement SS ones and they will last longer.

I use special brake grease when assembling.  Girling stuff is red and easy to find but I prefer the ATE brake grease as it is a bit more fluid.  Clean everything as above, grease the bore, seal and piston liberally.  Ease the piston back into it's bore.  It should go a wee bit hard but smoothly.  Fit the dust boot before the piston is all the way home.

Found black gunk and crap fluid?  Shame on you.  Completely flush your brake system with fresh fluid every two to three years.  All hydraulic rubbers and hoses need changing every 40K miles/60K kilometres.  I would just fit  new master and rear cylinders but overhaul the calipers.

[4129R]

Normally we don't separate the caliper halves.  Most kits do not include the seal between the two halves. 
Found black gunk and crap fluid?  Shame on you.  Completely flush your brake system with fresh fluid every two to three years.  All hydraulic rubbers and hoses need changing every 40K miles/60K kilometres.  I would just fit  new master and rear cylinders but overhaul the calipers.

The repair kit came with new seals of 2 types, both square section.

I bought this car in many pieces in a 40ft container, 2 cars in bits plus plenty of other relevant second hand spares. Not guilty.

[jbcollier]

Oops, didn't mean to attack you.  Sorry should have said so.  I know you're building from "scratch".

[4129R]

The bores of the two halves of he calipers were coated with a thin brown film. If I had not separated the two halves of both calipers and thoroughly cleaned the bores with a rotary wire brush back to smooth bare metal, then the new pistons would have got stuck in the bores again.

I tried using large grips, I held the pistons in a vice, I heated the calipers, and still these pistons were stuck fast in the bores, all 4 of them. Hydraulic pressure from behind forcing the pistons out was the only way they were coming out. Even when they were 3/4 of the way out, I still could not move them fro the outside, they had to be completely pushed out of the bores.

I have done 14 calipers and these were by far the worst.

The rebuild kit containing the square section caliper seals is the Triumph Spitfire one which has the new bleed nipples shown in the photo. Highly recommended. Triumph Spitfire MK3 MK4 (67-81) 2x Front Caliper Repair Kits & Pistons PK454D-2

[EuropaTC]

Another take on removing stuck pistons.....

If the caliper is on the car I usually remove the brake pads and press the pedal. One side at a time, it gets both pistons moving very easily and I've not used pliers/screwdrivers/levers in years to try and remove them. 

If the caliper is off the car I have an old m/cyl with reservoir mounted with a hand lever which I connect up and use that. I put flat steel bar (1/4") to replicate the disc, press away. Once one side moves I add packing to prevent it coming out completely and then the other side will start to move. It's straightforward to measure/pack until both only have a few mm to go, disconnect the hydraulic and pull out with fingers.

As for splitting the caliper, I tend to do that if it's been a while since the last rebuild. I never used to bother until I did a rear caliper and found some gooey sort of mess inside the square O ring between the caliper halves. Now if I'm not sure or if it was "new" to me, then I'd split every time despite the "you must not do this" warning that seems to be the rule these days. 

I must admit I just don't understand the logic on not splitting calipers when making up flared brake connectors, banjo connections, etc,  is deemed perfectly normal.

Brian

[jbcollier]

For a long time, the correct square-section, o-ring was unavailable.  If you split the calipers and reused the old o-ring, or replaced it with a generic o-ring, they would leak afterwards.  Never had a problem cleaning them out, did LOTS over the years.

[4129R]

It was suggested to me (by a very knowledgeable ex Lotus employee down at the local pub) that grease and a grease gun would be a suitable way of forcing the pistons out.

All you would need is some interface/union between the thread on the end of the grease gun, minus the nipple attachment, and a brake hose fitted to the calliper.

[EuropaTC]

It was suggested to me (by a very knowledgeable ex Lotus employee down at the local pub) that grease and a grease gun would be a suitable way of forcing the pistons out.

All you would need is some interface/union between the thread on the end of the grease gun, minus the nipple attachment, and a brake hose fitted to the calliper.

I've heard of that one as well, I think it must have been in one of the old "practical" car magazines that were around when folks actually worked on their cars. I could see it working because it's just another hydraulic method although of course it depends how hard you have to squeeze the grease gun !

The only thing I wouldn't use is air although I suppose if the calipers weren't split the piston can only fly as far as the other side of the caliper body.

Brian 

[4129R]

It was suggested to me (by a very knowledgeable ex Lotus employee down at the local pub) that grease and a grease gun would be a suitable way of forcing the pistons out.

All you would need is some interface/union between the thread on the end of the grease gun, minus the nipple attachment, and a brake hose fitted to the calliper.

I've heard of that one as well, I think it must have been in one of the old "practical" car magazines that were around when folks actually worked on their cars. I could see it working because it's just another hydraulic method although of course it depends how hard you have to squeeze the grease gun !

The only thing I wouldn't use is air although I suppose if the calipers weren't split the piston can only fly as far as the other side of the caliper body.

Brian

My pistons were so seized, hydraulic pressure was essential. A big grease gun would exert a good deal of pressure. I was not getting too much resistance when pumping the foot pedal. An even push all round from behind by hydraulic pressure was the only way they were coming out.