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MG MGA - master cylinder front plate

Can I replace the front plate gasket without dismantling the whole unit i.e. can one undo clevis pins and pull out the push rods. Will they just pushback in without annoying the pistons/seals?
H L Davy

Hi HL. Yes you can pull the pushrods, and pull off the master cylinder front plate to replace the gasket. The hydraulic pistons may want to pop out though, so an assistant would be useful, to hold the pistons in place, while the front cover and new gasket are being manouvered back into place. Cheers! Glenn
Glenn

Hi HL

The piston on the brake side of the master cylinder will definitely try and move forward when the front plate and pushrod is removed. This is because the brake system has a static hydraulic pressure of about 8 psi. This pressure is necessaay to ensure that the cups in the wheel slave cylinders remain expanded at rest. This static pressure does not sound much, but it will take a significant force to contain the piston within the master cylinder when the push rod is removed. Should the piston escape you will have hydraulic fluid where you don't want it and once you have cleaned up the mess you will need to go through the tedium of bleeding the brakes. You can replace the gasket most simply by making two cuts in the gasket from the top of the push rod holes to the top of the gasket. This way you will be able to slide the new gasket into place bewteen the front plate and the master sylinder body without removing the pushrods.
David MacFarlane

David;;
What is the advantage gained by cutting two slots for the push rods? This will leave a path for the brake fluid to escape. It is not hard to replace in situ. Just use common sense and replace it. All you have to do is use your finger to hold piston in place. The only pressure you will have is that of the spring.I have done this several times and with a properly placed cloth matt below it will not allow more fluid than that what has already leaked out to damage the finish,
Sandy Sanders
conrad sanders

The master cylinder end plate gasket and rubber boots around the pushrods are dust excluders, not fluid seals. If you have fluid leaking out of the master cylinder it needs a reuild. A new gasket alone will not stop the leaking, but only force the fluid to dribble out around the pushrods.
Barney Gaylord

I agree with Mr. Sanders as to the degree of difficulty in replacing the end gasket. I might suggest you replace the single gasket and add a second gasket, doubling the total thickness. Also, ensure the cutout for the brake piston is in fact large enough for the piston to slide through it. This will help prevent a swollen gasket from preventing the piston from moving fully forward on it's normal return and blocking the fluid vent port at the bottom of the master cylinder, possibly creating a hydraulic lock on the brake system. Just a suggestion. Marv Stuart
Marv Stuart

Why do you need to replace the gasket ? If you have sticking brakes in a rebuilt cylinder, then it should be easy (the pistons will not shoot out if there is no pressure in the system).

If the problem is a leak, then Barney is right, the cylinder needs a rebuild. NOTHING is worth more than good brakes, and saving money here is (frankly) stupid. I have just redone the brakes on a B for a friend of mine, where all the cylinders had been replaced, but the flex hoses were still the original 30 year old ones - at $10 a hose, I just find that mindblowing, especially when they were cracked....

Brakes and brake cylinders need service attention too, and do wear out, even when using silicon fluid. When using normal fluid, this is even more true. Rubber parts deteriorate, and should be replaced, just as they are in the service process of a modern car.

dominic clancy

This thread was discussed between 06/05/2005 and 09/05/2005

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