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MG MGA - Brake M/C seal fitting

Can anyone tell me if it is possible to replace the M/C piston seals without removing the M/C from the car , it looks straight forward enough even if I have to drop the peddles but any advise would be welcome, Vin.
Vin Rafter


Yes you can do it. But be careful if you are using ordinary brake fluid as any spillage will damage your paint work.

Drain the fluid out of the MC with a pipette or syringe.

Disconnect and remove the operating rods.

You may then find it easier to remove the front or even both MC retaining bolts to tilt the unit backwards for easy access. There is enough flexibility in the clutch and brake pipes to do this without the need to disconnect them.

With luck you may then find you do not need to bleed the system when the job is complete.

Steve Gyles

Steve, Tank you Ill try that, Vin.
Vin Rafter

Make sure to put an old towel under the piston openings as you remove the pistons, so you catch the remaining fluid from the bores. Have a watering can filled with hot water to immediately douse the area to wash off any that does drip onto paint.

Remove the towel asap to avoid letting any fluid soak through it, and throw it away to make sure you don't wipe down any paint with it afterwards.
dominic clancy

Depends how long your back can hold out! Not a big problem to do like Steve suggests, but for the sake of two more nuts you can work on the bench (or kitchen table, where it's warm!).

Forces you to bleed the system, which should be done periodically anyway! I spent another day and changed all the slave/caliper seals and rubber hoses too. They were all in good condition but over 10 (probably over 20) years old.

Neil McGurk

Thank you for your comments, the reason that im trying to do it in situ is that on removing the two retaining bolts I found that the front one fowls the heater box before it clears, like you neil Im in the process of renewing all the hoses and seals that I can, Vin
Vin Rafter


Seems like the previous owner/restorer mounted the MC before the heater box! On the RHD car the bolts should go in from the outside. i.e. the nuts should be on the heater side.

You could perhaps cut through the front bolt and install a new one.

Steve Gyles

Removing the m/cyl is tricky on RHD without bending the brake pipe because there is no banjo on the pipe and its v hard to get to it behind the cylinder. May be easier on LH drive.

You'll get a better job if you remove it and you can examine the bores to see if they are pitted, maybe get them re-honed or sleeved if necessary.

Another way to drain the fluid without mess is drain it through a brake bleed. Saves getting any fluid on the paint.

John Francis

Why didnt I think of that !!!
Vin Rafter

Stick with the towel whatever you do - there's always a bit of fluid that sticks around.

I'd cut the bolt and fit a new one. I'd also fit a banjo to the end of the pipe (that's a mod I did years ago)

dominic clancy

Vin, It is quite easy to take the pistons out and refit with new seals - I did this with mine a few years ago. The problem I had then was that the pistons were jammed in the master cylinder as the seals were too tight and I had to remove the MC to get some movement into them - wished I had taken the MC out in the first place. After working the pistons back and forth a dozen or so times everything worked OK when put back and has been OK since.
Cam Cunningham

Vin, I reconditioned mine last year without taking it out OR losing the fluid seal. Saves bleeding after the event, a great saving in time and effort.

BM Gannon

This thread was discussed between 12/01/2010 and 15/01/2010

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