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MG MGA - Master cylinder leaking

I have noticed hydraulic fluid stains on the rubber carpet on the right hand side (driver's side) of the car. On inspection I noticed that the brake side of the master cylinder was leaking fluid. I am assuming that the rubber cups and rubber seals inside the cylinder are worn and need replacing. I have one question here. Do I have to remove the master cylinder from the car to replace all the inards? or can I just replace them with the M/cyl still installed in the car. Sorry, I have one more question; I suppose if I remove the M/Cyl from the car I have to bleed the brakes all round. Do I have to bleed the clutch side too?

Will appreciate your help with this.

Frank
F. Camilleri

Frank

Where about on the MC is the leak? Is it the banjo end or the cover area by the pushrod?

It can be sorted insitu by removing the pushrod linkages and the 2 MC retaining bolts, then raising the front end. Be careful if you are using a fluid other than silicon otherwise you risk paint damage other than you may already have.

Steve
Steve Gyles

Thank you Mr. Gyles.

The leak is from the hole in which the brake pushrod goes in. There is no leak from the clutch pushrod hole.

I have silicone brake fluid in the system so not worried much with the paintwork.

When removing the retaining bolts, and raising the front end of the M/cyl, do I have to undo the clutch and brake pipes??. I would be extremely happy if I won't have to bleed both the brakes and clutch. Perhaps bleeding the brakes is quite a straight forward operation, and I won't have any problems with that. But bleeding the clutch is a different story. Also, at my age I have been warned not to crawl under cars. I'm 74 and with a past heart condition.

Regards

Frank

F. Camilleri

Frank

There is enough flexibility in the pipelines to allow the unit to be tilted up at the front end without undoing the banjos. I usually syphon out some of the MC contents before taking the front plate off and removing the piston. This avoids spillage out the front when you remove the piston.

Are your brakes working ok? Sometimes you can get a small seepage around that front plate gasket, so your seals may be ok. However, worth a look while you have it that far stripped.

I have found that I have managed to avoid a subsequent system bleed doing it this way. Once all back in place and topped up I allow time for the fluid to settle and for any bubbles to float to the top before operating the pedals.

Search "Removing the master cylinder?" in the archives and you will see the attached photo taken by Barry Gannon.


Steve

Steve Gyles

To answer your specific question. Yes the rubber pieces can be replaced in the car without removing either tube from the rear. The only consideration is you cannot hone the cylinder this way. If honed in the car this way there is no way to properly clean out any grit. Changing just the rubber bits this way is quick and easy. Bleeding brakes after is easier as ther in less air to remove. If you don't address the clutch side it won't need bled. But. The parts in there are the same age and it would be prudent to do both.
R J Brown

Thanks again Steve, and thanks too to RJ. The way you described the operation of replacing the rubbers inside the M/Cyl. seems to be quite an easy job. However, I am still a little sceptic about removing the old rubbers from the unit. What say you guys? How do I get to the rubbers inside?

Frank
F. Camilleri

Frank

When you remove the front plate the piston will probably spring out part way due to the spring pressure on the other side of the piston. You then just grab hold of it and extract. Make a note of the bits and their orientation as you take them out. The manual shows an exploded diagram.

Steve
Steve Gyles

Steve,

the way you explained everything makes a lot of sense, and is clear as crystal. Many many thanks for your time and advice.

Frank
F. Camilleri

Hi Frank
Had a leak from the push rod end with fluid collecting in the rubber dust seal cap. The M/C was new and car only on the road since December. However I guess that the seals had lost pressure. I have luckily used silicone fluid and apart from draining cylinder (as Steve suggested) I still had lots of fluid exiting out the bores. 2 issues worth noting. 1 I inadvertently bolted the M/C to mount with bolts facing heater. Big mistake. I could not withdraw the bolt to replace M/C in future. And 2 there seemed to be considerable pressure in both bores making it difficult to fit front pate and screws. All done now only need to bleed systems and fingers crossed leak resolved.
Good luck with your rebuild
Brian
Brian Paddon

There's a one way valve on the brake half of the MC which sits on a plain rubber washer at the other end of the bore. Easy to miss if you don't know its there. Bit of a mission to get it out in situ perhaps.
AR Terry

This thread was discussed between 03/03/2017 and 13/03/2017

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