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MG MGB Technical - MGB Brake Master Cyl

Helo everyone,

I am needing some info regarding MGB brake master cyl applications. Is it true that the mid years MGB's had a dual line mcyl? I am asking becuase I am considering this conversion for my MGA which I am using for competition. I figured it would be an affordable solution to ft/rr bias control with the addition of a valve. And of course safety would be greatly increased should there be a failure at either end.

Thanks!
John
John Bries

John,

You are correct. My 74 has a dual line master cyl. I'm not sure which years were covered. There are 2 lines leaving the mst cyl to a distribution block with a pressure warning sensor mounted on it.

Good luck,

Lamar
Lamar Crowell

John,

Yes, it's true. Dual-circuit brakes were the norm on NA cars from about 1968 until 1976 when the servo-equipped cars appeared. UK cars had an optional servo available in 1970.

I just converted my '77 B roadster over to the earlier system. Fairly easy to do. New master cylinder, used pedal box assembly and a "Switch and Body Assembly" (part #29, page 115, Moss catalogue) that mounts on the inner-fender side-wall to distribute the lines (unfortunately VERY expensive. Try to find a used one and put in new seals).

Not sure how it all fits in an A but would imagine it's not a big problem.

Cheers
Simon
Simon Austin

Thanks all!

Do you know if the 63-67 and 68-76 pedal boxes are the same?

John
John Bries

John, You bring up a good point in the safty of a dual master cylinder. Maybe someone can explain how they are safer than the single cylinder system. Ive found on every car that I've bled brakes on, in effect creating a leak situation the pedal goes to the floor. I don't understand where this is any safer than the early B system. The A system has the added problem that a clutch failure can cause a loss of brake fluid. Hopefully some can shed some light on this.
John
J Davis

John, If a single cylinder system fails on one end you have no brakes. If one end of a dual cylinder system fails you still have brakes on the other end. Yes, when bleeding the rear brakes, assuming you always bleed the rears first, the pedal will go to the floor. When you move to the front the pedal should not go to the floor. If it does something isn't right with the master cylinder or the rear brakes weren't properly bled or correctly adjusted. THe pedal will move closer to the floor than normal but there should be some pedal left. FWIW, Clifton
Clifton Gordon

John,
Did you check with the folks in NAMGAR about this sort of change? http://www.mgcars.org.uk/namgar/

I think you ought to as they may have an article on just this conversion in the backlog of tech articles featured in 30+ yrs of their magazine, MGA! At the least, they may know WHO to check with who has done this for personal safety and/or competition. Some folks I am aware of have used tandem M/Cs to accomplish the same end, but I think your idea would appeal to most MGA owners looking at the limited space available. You might check out Barney Gaylord's site, http://mgaguru.com/mgtech/ , perhaps he may have something there that can help you or he may be able to direct you to someone who has done what you wish to do. Good luck!
Bob Muenchausen

John,
Love to come over and see this as you do it and help if need be. I live in SE Denver, Monaco/Evans area.

J.T. Bamford

JT,
shoot me an email and we'll talk.

thanks
John
John Bries

A friend of mine races a Bugeye using a 68 - 74 master. Forget the later distribution block and run 1 line directly to the rear and the other to the original distribution block and use a plug on the connection that originally went to the rear line. You can easily install a bias valve to the rear brakes using this method.

This is how I'm going to set up my 67 also.
Mike MaGee

This thread was discussed between 06/03/2004 and 10/03/2004

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