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MG MGB Technical - Cluch slave cylinder piston stuck

I'm in the process of trying to rebuild the clutch slave cyliner from my 67 GT. The main problem is that the piston appears to be stuck! I've soaked it in penetrating / release fluid for 24 hours, put 150psi from my compressor into the back end, tapped it sharply against a wooden block etc etc all to no avail!! The only route I haven't explored is using any heat. The obvious thing is to pipe it back up to the master cylinder & apply pressure that way, but that is just not possible due, since I'm in the middle of a 'nut & bolt' rebuild. Any other suggestions?
N Dring

Sometimes they get a bit cocked in the bore. Try using a C-clamp or bench vise and pressing it in a little to free it up. Careful with that much air pressure. If it pops loose, you might find it's around Paris before it returns to earth.
tom (member)

Thats odd, I have changed the seals on mine when they have been disintegrating and debris was packed around the piston, never a problem getting it out. Tapping it in then trying air pressure is good advice.
Stan Best

Gentlemen - Applying air pressure behind a stuck piston is a good way to become injured in the split second that the piston breaks loose. If you must do it, drape the cylinder with a heavy blanket or such to catch the piston as it rockets out of the cylinder. I would hate to see a posting on one of our members in the emergency room for the removal of a clutch slave cylinder from the side of his head.

That said, a better approach is to rig up a bolt that will fit in the inlet of the cylinder, with a through hole and a grease fitting installed. Screw the modified bolt in place, apply the grease gun and start pumping. This has the advantage that far more force can be developed with the grease gun than with compressed air and the piston will move out only as fast as you can pump the grease gun.

If you try using heat to loosen the piston, make sure that either the inlet hole in the cylinder, or the bleeder hole or both are open and free of any obstruction. If there is no way for the cylinder to vent the heated air inside, the results are more dramatic than with a compressor (I have a rather dismaying dent in the ceiling of our garage as a result of not paying attention to the venting of a brake cylinder while heating it as reminder to be careful - thank goodness in the ceiling and not me).
Cheers - Dave
David DuBois

Under some conditions, the steel piston and the aluminum housing can become corroded together. Sufficiently so that removal of the piston is impossible. I had one, removed from a parts car, that was this way. Soaking on penetrating oil, totally immersed, for six months did not allow the piston to be released. I suspect that, under such conditions, the bore of the housing would require re-sleeving if it were to be used and the piston would have to be replaced.

Under such conditions, it might be better to replace the existing unit with a new unit. Then, you can keep track of how it has been maintained and how many times it has been rebuilt. When I checked into rebuilding, the price of a rebuild was, from one company, about 80% of the price of a new slave cylinder. From a second company, the cost of rebuild was 205% the cost of a new slave cylinder.

Les Bengtson

This thread was discussed on 29/10/2007

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