Lotus Elan and Lotus Elan Plus 2 Forums

Does anyone have a good method of removing the piston from a master cylinder? It's not frozen in place because it can be pushed in. But I can't find a way to pull it out because there's nothing to grab. The circlip, washer, pushrod have been removed, of course. Compressed air does nothing.

Art
26/4934

Try applying some air pressure in the same direction that the fluid normally goes. Footpump or compressor does the trick. (works for caliper pistons too).
Don't stand in front of it if you are using a compressor!
Hamish.

Hamish,
50 psi didn't do it - should I use higher pressure?

Try pushing the piston back in, then use air, then back in, then air, just to get it moving backwards and forwards. There is probably some hard 'gum' where it usiually comes to a rest that needs a little persuasion. I use 120psi...and stand back!
Mark

Try a good soaking in meths-or whatever the us equivalent is??

Art,

I would buy a new Master Cylinder.

Ian

Art,

If its like my 72 +2 Elan the master cylinder has a allen head bolt that holds all the guts of the brake master cylinder. You will need to remove the plastic reservior and then using the (large) allen wrench loosen the bolt. Guts should come out with some air pressure.

If the air pressure doesnt work, find a old brake line and proper fitting hydralic brake connection to the master cylinder, then hook up a grease gun and pump some grease. A little measy but works when air pressure method fails.

I think your problem is the allen head bolt in the metal body of the cylinder. I had the same problem when rebuilding my MC on the Lotus.

Regards,
Ty
Tiger, Healey, Morgan, Lotus, 2 MGA's

I would resort to Mark's (Elanintheforest) method if it didn't work first time. I would also use good ol' WD40 as well. SHould come out OK.

I owuld say that you would only need to get a new master cylinder if the old one was all scored. Try a bit of fine steel wool in the bore whn you can get at it. Then was it all out with fresh fluid. Did that with mine and it's been fine for a couple of years.

Hamish.

Thanks to all for the ideas. It's moving in and out a bit with air, and now I'm soaking it overnight in solvent. The biggest problem has been stopping up the reservoir to prevent air flow back through it. An old tee shirt sleeve just about fills the reservoir, but a little air still seeps out around it. The screw top in the reservoir isn't anywhere near airtight.

Art

I think the reservoir cap is supposed to have a vent hole in it somewhere to allow air in/out as the fluid level changes.

Matthew

Art,

Try a plastic food bag over the top held down by the cap (this will seal the breather).

Ian

Together with the plastic bag under the cap, I would also suggest that you hold the MC cap end in a clamp. I have had a few caps blow off when using compressed air to remove the piston. And put a small box partially filled with soft foam rubber (or similar) over the piston end.

Please take care, mineral based oils swell the seals which makes matters worse.
Once the circlip is removed, just tap the open end of the barrel on a wooden block (won't damage the cylinder casting), inertia will do the rest.
worth pushing the piston in and cleaning the visible bore first.
J

Thanks to all for the suggestions. I finally got the little rascal out yesterday (other things like work, garden, home repairs, etc.) intervened. I know it's a lame excuse, but it's all I have. What finally did it for me was a combination of push in/lubricate bore with hydraulic fluid/apply 140 psi pressure after finally finding the right substance to seal the top of the reservoir. This turned out to be a rubberizesd fiber gasket material that had just enough give to provide a sufficient seal. It still took three of the above cycles to make it work, but it popped out into my pile of rags with a satisfying "ploop". The cylinder bore is perfect - it was just the dry old seals that held it all in the bore. The repair kit goes on today, and then I can do the brake master cylinder.

Art

frearther wrote:What finally did it for me was a combination of push in/lubricate bore with hydraulic fluid/apply 140 psi pressure

Applying air pressure like this is just a disaster waiting to happen, are you after a place in the Darwin awards?

If you REALLY need to use air pressure then bolt the cylinder to a piece of steel plate maybe 1/4" thick. Space the open end partly away with a few nuts or washers and use the lowest pressure you can get away with. 140psi applied to a system with unconstrained parts is IMHO just plain daft.