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MG MGB Technical - Brake Master Cylinder Replacement

Hello,

My car is a 1973 MGB. About five years ago and only 8,000 miles I had a new brake master cylinder installed when I was rebuilding/replacing/restoring everything.

Now, since early spring, if I let my car sit for any period of time - more than a week - when I get in the car there is a small puddle of brake fluid on my floor mat, where it has drained down from the brake pedal from the master cylinder. The master cylinder is leaking through the main rod.

So, it looks like I am going to have to replace the master cylinder and I have a few questions:

1) Where is the best place to get a new master cylinder?
2) Am I going to be able to buy a new one or will it be rebuilt? Does it matter?
3) Can I rebuild mine? I have read in the archives that you should not do this and it is better to replace it.
4) I have worked on American cars all my life and I have replaced many master cylinders. This will be my first one on my MGB. Is changing it the same as an American car? Are there any secrets/tips/tricks I should know?

Thanks in advance for your help.

Cheers,

Robert
Robert Browning

Robert,

The general feeling you'll read is that the brakes stop the car, so don't take any chances on a rebuild on the master cylinder. I applied this theory to my 73B roadster early this summer and bought a new brake master cylinder when I did the system.

However, I rebuilt my clutch master and slave cylinders. This worked great for about 8 to 10 weeks until the master cylinder began to leak at the same point as your brake cylinder. I replaced it with a new one this weekend.

On my car the components were original....which makes them almost 35 years old. No matter how good the fluids used there will be some moisture in the system over time that is going to cause corrosion to the cylinder walls.....at least that's my take on it.

I like your idea of asking where to get the new one. I think personally I would go that route if I were in your shoes.

BH
BH Davis

Robert,

1) Where is the best place to get a new master cylinder?

Moss, VB, BritTek,

2) Am I going to be able to buy a new one or will it be rebuilt? Does it matter?

I would buy a new one.

3) Can I rebuild mine? I have read in the archives that you should not do this and it is better to replace it.

Yes, you can but better to buy a new one.

4) I have worked on American cars all my life and I have replaced many master cylinders. This will be my first one on my MGB. Is changing it the same as an American car? Are there any secrets/tips/tricks I should know?

I rebuilt the brake booster myself and that worked out great. I don't think you have one on your car. When it came to the MC that was easy also. Nothing hard about it. I know you can do it.

Ray
Ray 1977mgb

Robert. The brake master cylinder on the 68-74 1/2 cars, North American specification, is somewhat more difficult to rebuild than the early single system and later servo-assisted dual brake system.

Last time I checked, Northwest Imports had the best price on new brake master cylinders.

I am afraid that I am the source of the common "buy a new one rather than rebuild an old one". Many years ago, I mentioned that I was replacing my master cylinders with new ones as part of the brake service. The reason is that I would then be starting off with a known quantity--a new master cylinder which I could keep track of over the years. The master cylinders on my cars were all original, I did not know how often the brakes had been serviced (should be flushed every two years and filled with fresh fluid if you are not using Silicone), nor did I know how often they might have been rebuilt in the past. Hence, my decision to replace the master cylinders with new ones rather than attempt a rebuild. This logic seems to have caught on with others and I commonly see the same reasons I posted many years ago, being given out by others today.

This does not, necessarily, apply to your case since you had a new master cylinder installed, know your maintenance history on the brake system, and have some experience at rebuilding such systems. In your case, rebuilding the master cylinder, should you desire to attempt it, would make perfect sense. Just note it in your maintenance logs, note any problems you found when doing the rebuild, and note the bi-annual system flushes. You are, already, at the point that my "buy new" advise was intended to get all of us to. You are dealing with a known quantity.

Les
Les Bengtson

This thread was discussed between 21/10/2007 and 22/10/2007

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