Hi All,
Can anyone recommend a good pentrant for loosening stuck caliper pistons. Seals are perished-pistons won’t budge!
Thank you,
-EvanCC
1969 FHC - making progress for the first time in ten years!
Do you think the caliper pistons are any good? Or do you intend to change them for new steel or aftermarket stainless ones?
When I did mine, I knew the pistons were rusted to hell (had sat for around 40 years with bad or no fluid), so I drilled holes in them, ran a tap through each, and then screwed a bolt in to ground inside the cylinder and push the piston out. Another way is to attach a Zerk fitting to a spare banjo and pump the caliper full of grease using a grease gun. The pressure usually pushes the pistons out, and you can reuse the majority of the grease on your next caliper if you’re adept at disassembling and reassembling the grease gun on the fly. Problem is then you have to use some solvent (brake cleaner comes to mind) to remove the last of the grease from the small internal passages inside the caliper.
Good luck!
If it’s only seals perished (as opposed to pistons rusted in place), I’ve found that two screwdrivers levering from opposite sides into the piston groove will usually budge them.
Also a G clamp can be used to push the piston in a bit (yes the opposite to the direction you want it to go) and that breaks the seal and allows it to come the other way
Robert
I’ve had pretty good luck using compressed air but be very careful as the pistons will come out with a great deal of power and you will not want any part of your body to be in their path. Good luck.
A wooden spacer between the two pistons is a good idea if applying pressurised air, grease, fluid etc. Otherwise one piston will come out, whilst the other is still stuck. Once one piston is out, all the pressure will be lost.
Regards
Gerry
took my calipers off, sprayed loads of WD40 into them, attached a footpump to pipe, pump and leave over night.
Compressed air may help but the hydraulic pressure is typically many times higher so, if they are really stuck, 120 psi probably isn’t enough.
I’ve managed to shift really tight pistons by taking the calipers off, draining off as much fluid as possible and filling with water. I then blocked off the pipe entry and put the whole into the oven with a block of wood between the pistons. As the water boiled, the pressure pushed the pistons out and sprayed the remaining fluid around the oven!
Mike
Mike, nice one. Hope you used a self cleaning oven!!
Regards
Gerry
Play safe and send the calipers for overhaul at:
Classicar Automotive
Unit A,
Alderley Rd,
Chelford,
Macclesfield,
Cheshire SK11 9AP
e-mail: [email protected]
Tel: 01625 860910
No connection apart from a happy customer.
Beat me to it! No sense in making life harder! 
Years ago, with my first Elan, I had a seized piston in a rear caliper. Although it said never to split the caliper, a friend who had toolmaking expertise and a lathe in his basement thought otherwise. We separated the caliper halves and he carefully machined out the piston until the walls were paper-thin, then collapsed the old piston and replaced it with a new one and seal kit. Keeping the mating surfaces “operating-room clean” we reassembled the caliper and I never had a problem with it afterward. Always more than one way to skin a cat! 
A tip my father gave me… One option if you’ve got a seized piston on one side of the caliper and haven’t yet taken it off the car is to swap the now unevenly worn pads from one side of the disc to the other and give the pedal a big shove.
C
[quote=“Galwaylotus”]
Always more than one way to skin a cat![/quote]
When you have the right equipment - anything is possible 
Even though I have the equipment, I still sent my rear calipers to the experts to refurbish. The front calipers will go to them next winter.
Thanks fo the replies!
Some background…
The question was prompted by the Brian Buckland book, wherein he recommends soaking in parafin as a penetrant. I’d never heard of this before and was wondering if I’d missed a trick. Seems to me that parafin would be difficult to remove aftrward.
Some more details…
Car has been sitting for a little over ten years.
Brakes were locked onto the disc.
Planning on stainless pistons and refurbishment by someone who can do the full treatment. I’d like to get the pistons out so I have a better idea of what I’m asking them to do.
Thais again.
Evan CC
I’ m familiar with Classicar Automotive, but can anyone recommend a shop stateside that could provide a similar level of service?
Evan CC
Evan,
Parafin (kerosene here in Oz) would be no harder to get rid of than grease, water etc.
Colin.
EvanCC,
White Post Resturations rebuilt the rear brakes on my 308 about 10-years ago and they are still working without issue. Their website is:
Bill
In that case I like the grease gun idea…but I’d be using rubber grease
Using rubber grease might get expensive! 
I don’t see why even an amateur can’t rebuild these calipers. They are not that quirky, especially the fronts. The rears may take some fiddling to get the emergency brake to work properly, but nothing some tinkering won’t fix. Seals, including cross-over seals, are readily available, along with stainless pistons–and you’ll save some money.
These are very easy to rebuild. I used Kroil on mine. Let them soak for a few days. I then used compressed air. I put a towel over the piston so that it would not shoot out too far. Well, it shot right past the towel, accross the garage and put a dent on the inside of my garage door. So be careful.