Morris Minor Owners Club

Can anyone offer advice on how to remove a piston from a brake caliper, they have been unused for a number of years and I want to replace the seals and paint before use, but need to remove the pistons, they seem solid. These are from an MG Midget that will be fitted to a Minor Van

Look forward to any advice

RussLCV@clubMorris.co.uk

Well if they were still fitted to a car you could champ one in place and use brake pressure to push the other one out but off the car you would need (I assume) some sort of hydralic assistance as I dont think compressed air would be enough.

Cheers Kevin

They are not on any vehicle so I am at a loose end with these

Russ

Hello Russel,

the way I have done these is to drill and tap a 3\8" UNF (almost certain that is the thread but just try it?) bolt to take a grease nipple then using a grease gun to force out the piston.

Alec

Heard that fpr cylinders but sure if it will work for calipers but will give it a go

Russ

Hello Russ,

I have used it on calipers and it works.

Alec

The calipers are 3/8" unf - and by chance I discovered that if I unscrewed the adapter from the end of my grease gun extension tube - it too was 3/8" unf - so it screwed straight on and pumps the pistons out nicely. Of course as soon as one piston starts moving thats where the grease goes - so I had to make simple clamp to hold the piston at the grease gun side in place and then pumped the other one out and so on until both were moving - then pump them both to full extension - and wiggle them out. The caliper obviously then needs thorough cleaning to remove all traces of grease.

If you've got an old master cylinder (any will do Minor or not) and a bit of pipe with the right ends, you can also rig it up to pump the piston out. I've managed that way in the past with a pretty stuck caliper pumping the master by hand, but it was hard going.

Other than the grease getting in everything, the grease gun idea sounds far better - Maybe worth using an easy to clean out grease, or that red stuff used in brake cylinder assembly maybe?

Hello Packedup,

the grease is easily cleaned out and of course the calipers and pistons will need to be washed in solvent also before re-assembly. Assuming of course that they are not corroded.
I think that you can get more pressure from a grease gun than a master cylinder as well.

Alec

In theorey the grease gun is good for 10,000 psi!!! Car hydraulics normally work at around 300 psi - maybe 1000 psi in an emergency.
What is that RED grease used on cylinders - anyone know ? I just use silicone vacuum grease from RS - but it's not red.
I cleaned out all the little passages with pipe cleaners, and meths for solvent - then final cleaning with brake fluid.

Hello BMCE,

I don't know what the red grease is but whatever is used on hydraulic (car) systems should not be petroleum based. Methylated spirit is so you need to be careful in it's use. Although it is often the recommended solvent for cleaning brake components it should not be used when the seals are involved e.g. to flush out a system.

Alec

Oh the meths is just for cleaning the metal parts (probably because it evaporates away quickly) - followed by brake fluid. I have had no trubble so far with the silcone grease.

bmcecosse wrote: What is that RED grease used on cylinders - anyone know ?

Absolutely no idea, all I know is it seems to come with decent seal kits, and I've seen it for sale in small tubes at good trade type factors. It's also what seems to be found in NOS cylinders, although at that point it's usually dried up a fair bit!

I've had too much fun trying to clean out calipers thatsimply have 30 years or crud in them, which is why I wouldn't much fancy trying to clear out normal grease from them... If the seals are being replaced then meths seems to work very well on the metal parts

bmcecosse wrote:What is that RED grease used on cylinders - anyone know ?

It's rubber grease.

Castrol Red Rubber Grease
Special rubber compatible grease for use on hydraulic brake and clutch components where hardening or swelling must be avoided.

Well done Scott! Sadly my seals are black, so this grease (exclusively for red rubber, it appears) will be no use.

BMC, err... are you joking? I'm never quite sure!

The 'Red Rubber Grease' is red grease for rubber, not grease for red rubber

As for unsiezing stuck cylinders the common method on the bike is to (insert a bit of wood in the calliper) and then pressurise it using a foot-pump. This does work on stuck callipers (the MZ ones are prone to corroding 'cos they used a cheap alloy when they copied the Brembo design). Just make sure you're not going to be hit by flying bits of piston.

bmcecosse wrote:Sadly my seals are black, so this grease (exclusively for red rubber, it appears) will be no use.

LOL
Put it on thick enough & they'll turn red .