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MG MGA - master cylinder-at a loss

Earlier this winter I rebuilt the seals in my master cylinder. I reassembled it and put the pistons back in dry (i.e without smearing fluid on them).

While assembling the clutch piston went in a touch and didn't slide back. I put the master cylinder back in the car and loaded the reseviour (sp) with silicon fluid assuming that the fluid would lubricate the clutch cylinder and it would slide back in place.

Well the opposite has happened. I touched the clutch pedal to move the cylinder into the fluid and the piston is now stuck at top extention!

I now have the master cylinder out of the car and have been trying to blow the pistons out with no success. I don't have a compressor so I've been using a garden sprayer pressure tank with a fitting to both the fill hole and the fitting hole on the clutch side. All to no avail.

I'm going nuts..... how can this thing be frozen in there so firmly????? I just cleaned it out.

An more importantly how the heck do I get it out?
Tysen

You will need higher pressure than the garden sprayer can generate. Maybe visit your local gas station to use a hign pressure air hose.

Always wet the seals with brake fluid during assembly. If a piston doesn't want to return you can use air pressure on the output port to bring it back. You may have to cycle the thing repeatedly to get it to loosen up so it will return with spring force only.
Barney Gaylord

Hi Tysen. It is easy to get a seal in backwards, or for the seals to not be completely seated. As Barney stated, master cylinder seals and components need to be assembled using a suitable lubricant. Failure to do so can cause the seals to rip during installation on the piston, and can also cause seizure in the bores. My guess would be that a seal is not quite seated properly. When you get the pistons out, I would thoroughly lubricate the rubber seals, and try re installing them, making sure that they seat properly on the pistons. Good luck. Glenn

Glenn

Also, make sure that return holes in the tops of the bores aren't clogged. This will also make a piston stick.
Mark

Tysen, the pistons in both my brake and clutch were completely rusted solid. I got them out by inserting an expandable concrete anchor into the hole in the piston and pulling on the anchor with a slide hammer.

Andy
Andy Preston

Hi Tysen, I did exactly the same thing with mine two years ago. A friend suggested blowing it out and we used a standard tyre footpump. I clamped it tightly against the inlet with my hands and some sealant while my friend stamped on the pump. After about 10 goes and about to give up - it finally flew out. Initially we had a cloth wrapped around it but by the tenth go I wasn't expecting anything so dropped the cloth, when it blew out with a bang just missing my face and bouncing off the wall - so take care. When putting it back in we made sure it was well lubricated and that the rubber seal was worked in gradually - bedded in by pushing it up and down with a screw driver. Make sure you get the non return valve in the brake side not the clutch - when we disassembled mine, the PO had reversed them - which is why the brake cylinders leaked fluid -good luck cheers Cam
Cam Cunningham

I fought that problem for at least a week. I was fortunate to always get the piston out by jamming a flat screwdriver into the hole in the piston and rotating the piston while trying to pull it out. It still would not move freely in the M/C. It turned out that the piston seal was not completely seated on the piston. When the seal is properly installed it will have the same profile as an uninstalled seal. Barney's web page has a really good picture and also provides a last ditch method of using a grease gun to get the piston out of the M/C.

Good luck -

Don
D. R. Carlberg

Yes ... same problem here too last year. Just went down to my local MG garage and they blew it out with their airline - no charge - they get enough money from me anyway!
Just watch that you hold the open end of the cylinder against a hard surface as you blow it out. We nearly lost all the springs, gaskets, everything in an explosive bit of grape shot around the room.
Richard Ross

Blowing it out with air can be dangerous, so be careful. A neat trick, and a safer method, is to pump up the pressure using a grease gun. Make an adapter that has a zirc fitting (grease nipple) and then the grease gun will slowly force the piston out. Afterwards, just make sure to clean all the grease off of and out of everything. I have used this method many times on stuck Honda motorcycle calipers, but never in this application, so I don't know how hard it would be in practice, of if it would be practical at all here...so just my .02...
AJ Mail

Listen to Barney.
mark lanctot

This thread was discussed between 25/02/2006 and 11/03/2006

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