MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Master Cylinder rebuild

Maybe I should have posted this here instead of B General!

I'm part way through a rebuild on our 1979 B master cylinder. Everything was going just fine until it came to removing the pressure differential piston assembly, it is frozen solid in the bore and ain't moving!

Any suggestions as to how I can get it out?

I'm hoping the bore it sits in is still in good shape, the main bore was almost perfect and just needed a wire brush on a dremel running through it a couple of times. The frozen piston does worry me slightly.
The Wiz

Try soaking it in rust pentrating solvent overnight. If that doesnt help John M usually has good results by heating the parts up REALLY hot. I'll be over there tomorrow andwill try and get his ideas. If there's time drop it by and I'll look at it. (I may havea spare off a '70 parts car I have too)
william fox

I was wondering about heat, I was just scared to put the blow torch on the cast iron body!
The Wiz

What's wrong with heat on cast iron? Come on, I though y'all did this sort of routine stuff on the dining room table!! Torch it.
Paul Hanley

William. The master cylinder on the RB cars is different than the one on your 70.

Wiz. Have you considered a new master cylinder? Rather than rebuilding, I am replacing the old ones with new ones. I have replaced two of mine with one left to go. My reasoning is that a 25+ year old master cylinder may have been rebuilt any number of times in the past without my knowing about it. Hence, I am taking the opportunity to replace the old ones, on an as needed basis, with new ones. Then, I am starting from a know quality base and would expect them to last through the remainder of my life time. After that, it is someone elses problem.

This being said, get a socket that fits the bolt properly, grind off the beveled part on the end of the socket (the lead in--use a grinder or belt sander and cool it by plunging it into a bowl of water to prevent overheating while grinding/sanding). Like the the flywheel bolts, the head on that bolt is shorter than standard and a non-modified socket will tend to slip off. If you can get a six point socket to modify that would be best. If you go to my website and check the tooling section (under MG), you will see a picture of a modified and unmodified socket. If, with a properly modified socket, you cannot get it apart, heat is the next step. Les
Les Bengtson

Mike: John checked the book. Take out the pressure failure switch on the bottom and shoot some rust penetrant in there too. Then try shooting air in there through the primary outlet port as per the Haynes
william fox

Thanks for the advice all!

Paul, blowtorching is done on the kitchen counter, not the table! :-)

Les, a new master cylinder will be purchased if necessary, the thing is, we do know the history of the car from 1985 onwards, the master cylinder has had one rebuild and the main bore is still in excellent shape. The bolt you are describing came out with no problem, it is the piston behind it that won't move unfortunately.

Bill, our compressor only goes up to 125PSI, not enough to shift the little bugger! :-)

I will try the blowtorch although if the piston is rusted in I am probably going to have to buy a new cylinder anyway. I am hoping that it is just gummed in with crud, that would then just clean up and be useable.
The Wiz

time to try some HI-TECH solutions on it!!
william fox

The WIZ

IF you have the time try soaking Kroil, PB Blaser, or similar, down into it for a number of days. I have had some stuff come loose after a week or more of soaking.

Is there any way to adapt a fitting to pressurize it with a grease gun? Much higher pressures with a lot more safety than compressed air.

FWIW

Larry
Larry Hallanger

This thread was discussed between 14/02/2005 and 15/02/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.