I'm overhauling a set of subaru 4 pots, I've split the calipers in half and I'm struggling to remove a couple of stuck pistons. I don't have access to compressed air, some came out by hand but some a more stuck

Any ideas on how I could get them out with hand tools?

 

I did the same job about 2 weeks ago.

There are a few options. The easiest technique when in your situation is to use self-grip pliers ('Mole'). If you use the largest one of the standard set of 3 (I am presuming that you have these) and grip the piston just above the notch. Even if you damage the rim of this with the pliers (which you probably will), then if you need to reuse the piston, it shouldn't matter because this part always remains outside the piston recess. If you are getting rid of the piston (s) then you can grip it anywhere. Once you've got a good grip then rotate the pliers/piston to and fro to remove it.

If that doesn't work the second option is more trouble. You need to rebuild the caliper and connect it back up to the brake pipes, bleed out the air and then use the brake hydraulic pressure to push out the piston. To achieve this, you'll need to place a wedge between the two upper or lower pistons and a G clamp to stop the non-seized piston from moving. This will then transfer all the force to one (seized) piston. Press brake pedal hard.

If more than one piston seized then you'll need to move the clamp (s) around a bit until the pistons are partly freed and then finish removal with pliers.

D.

 

ps you don't need to split the calipers to renew seals and pistons. I guess that it might be a bit late for that advice.

D.

 

Thanks for the advice, will give it a go now

They needed to be split as I wanted them shot blasted / powdercoated as they were looking very grubby and made it easier to get the horribly seized pins that hold the pads in place out

I'll let you know how I get on

 

Have you got new ring seals to join the 2 halves of the calipers back together?

 

Worked a treat, all pistons out and undamaged

No not yet, haven't bought anything to refurb them yet, just thought I'd crack on with getting them apart first

 

Contact ian godney @ goodspeed brakes on here, he does a full refirb kit which has all the seals ect, and you can also get alloy pistons and they will never seize again, if your planning on keeping the car it's a worthwhile upgrade.

 

I have caliper half seals spare.

 

Replaced seals and all pistons with stainless steel a few months ago. Brakes have felt ok although recent MOT nearly failed due to unbalanced brakes. Slight judder due to previous overheating when old pistons were seized. Decided to replace discs and pads today. Couldn't believe it. One of the near side pistons is seized again. Couldn't budge it by any method. I thought that this didn't happen with stainless steel pistons.

Anyone else had this?

D.

 

It has nothing to do with the pistons as they cannot rust , it will be the top of the bore in the caliper has gone rusty and making the piston tight in the caliper , did you clean the bore with emery cloth to completely clean them up ? And we're the dust seals all in place , if these come unclipped then the damp can get into the bores and rust them up .

Cheers Ian

 

Mixing stainless steel with (I assume), cast iron (or cast steel) callipers in the presence of an electrolyte (ie the water in your hygroscopic brake fluid) will cause the callipers to rust like mad, as they are several places apart from stainless steel on the table of electro-negative potential.

If your callipers are non-ferrous, it will be even worse.

If you use emery cloth to clean the calliper bores up, that can potentially embed particles of the abrasive into the calliper material which will lead to further corrosion between the particles and the calliper. So you need to check to make sure there are no embedded particles when you're finished.

Put simply, dissimilar materials in contact, in the presence of an electrolyte, will generally lead to corrosion. Have a look here for further details:

http://www.npl.co.uk/upload/pdf/bime...1105114556.pdf

I know a bit about this. Sadly though, I can't tell Stork from butter.

 

Thanks Ian. No didn't use sandpaper on bore but to be fair, the bores themselves looked corrosion free and pistons did move freely when first installed. Dust seals are intact. What would you suggest?

D.

 

Ps bled through brake fluid at time of calliper rebuild such that brake fluid has been in effect been replaced.

D.

 

Hi
I disagree , there will never be enough water in the brake fluid to make them ' rust like hell ' , we have been fitting stainless steel pistons into calipers for many years now and have had no problems to date , I think the only warranty claim we have ever had on calipers fitted with stainless steel pistons was a rusted top lip in the bore after the dust seal had become unclipped allowing the damp inside the caliper.

I understand the problems associated with dissimilar metals , but in my 20 years experience with brakes , we find the weather causes just about all caliper related problems

Cheers Ian

 

That's most interesting, thank you.

 

Sorry to hijack a very old thread but just wondered how to split the 4pot. I refurbished some old ones to relaid my smaller 2pot but didn't split them wanted to sandblast and paint them up and replace piston.