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MG MGA - TRW Master cylinder woes

Hey all, after 40 months of effort, I took the MGA around the block yesterday. It's a good thing I did not go far as the brakes would not release. After reading Barney's site again, I have determined that the master cylinder is not releasing, per his site.

Now to the question. Can the master cylinder be repaired in situ? Can it be disassembled and reassembled without a system bleed? Thanks, Tom, hot to drive the darn thing!
Thomas McNamara

Yes. Extract as much fluid as possible from the reservoir. Place rage underneath the master cylinder. Remove pushrods and end plate. Try to leave the clutch side piston in place. Extract the Brake side piston and other internal bits for repairs. After reassembly, fill the reservoir before pumping the pedals. If all goes well, and you haven't disturbed anything downstream, a few pumps of the pedals should get fluid into the master cylinders and bring the remaining air back to the reservoir. With a little luck you may not need to bleed the system.
Barney Gaylord

Thanks Barney, for this and your site. You da man! :) Tom
Thomas McNamara

A TRW master cylinder is on it's way to me as you read this. Running with the wrong 3/4" MC for 10 years, complete with a broken plastic anti-return valve (shock). A spare unit I have needs sleeving and a new spring that lost its temper. I'm just going to break the new one down when it gets here and modify before installation. A 1mm bit is the smallest I can find commercially. It's a bit larger than a 1/32" bit. Hope it does not release too much pressure thus defeating the purpose.

May have a 3/4" unit for sale to one of you Sprite owners! Good bores!

Good luck Tom and thanks to Barney.
Tom Baker

Hey all, I to am having difficulty finding a 1/32 inch drill. Would a 1/16 inch hole be too big? That size is commonly available but is twice a big. Thanks, Tom
Thomas McNamara

Hey all, I too am having difficulty finding a 1/32 inch drill. Would a 1/16 inch hole be too big? That size is commonly available but is twice a big. Thanks, Tom
Thomas McNamara

Thomas, what are you drilling?
A 1/16 drill is 4x the hole area of a 1/32!
Art Pearse

Thomas
You will find the bits on Amazon or eBay

dominic clancy

TRW master cylinder arrived at 5:30, by 6 the anti-return valve was modified and the unit was re-assembled. Swapped the clutch elbow complete with new copper washers, replaced all hex bolts with the original slotted screws, light coat of poly and will re-install this weekend. No worries of sticking pistons as the action seems fine. Wonder what the clutch action will be like with the correct master cylinder installed???
Tommy Baker

Hey, needless to say, THANKS! The saga; I was finally able to find a 1/32" bit. It came with other small bits as a Dremel kit. When I got home with it I discovered that the Dremel oolets I had were too large. The next day I got a collet set and disassembled the M/C in situ.

Next, drilled the hole, reassembled the M/C and refilled it with DOT 5. No Brakes! Spent the next 3 days getting the air out of the system. Now I understand "bench bleeding!

Drove "around the block" today with no issues. Regards, Tom
Thomas McNamara

Strange how this was such a drawn out affair.

I fitted my new Caparo MC before Christmas, and didn't have time to bleed when I was done. The weather has been so awful, I only went back to do it last weekend.. To my great delight, when I tried the pedals I had firm brake and clutch operation - the air in the MC had apparently worked it's way back to the surface and the pedals are both rock hard. The drive around the block confirmed everything was fine.

Then it started snowing (again).
dominic clancy

Great, Tom. Next time try gunson's Eezibleed. Makes bleeding and flushing the hydraulics a one person job. Well worth the price of the kit in the frustration saved.

Dominic, I've nver been that lucky.
Tom Baker

Hey Tom & all, in retrospect, I think that there must have been air trapped in the master cylinder that was trapped by my filling the reservoir?

All's well that ends well. :) I hope to put plates on it shortly. Who-hoo! Tom
Thomas McNamara

Hey Thomas, I've been following this thread, always interested in learning something about our cars. What part were you drilling with the 1/32 drill bit?

Thanks, George
G Goeppner

Hey George, rather than re-invent the wheel, go to MGAguru.com. Nest, search for "master cylinder". He has pictures and directions there. After all, he is the "MGA GURU"! Be well. Tom
Thomas McNamara

This thread was discussed between 25/03/2013 and 02/04/2013

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