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Master Cylinder - Brake

Posted by docajay 
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docajay Avatar
ajay h
belize city, Belize   blz
1978 MG MGB
Good day one and all in MG land,

I am back, and this time it is because of the brakes. The story goes as fine day I noticed brake fluid under the car so I did some investigative work and realized one of the lines was leaking. So I proceeded to change all the lines. Upon getting the car back, it was working fine. Just a little pressure on the brake pedal produced great resistance and resulted in the car coming to a halt. After using it for couple of times I noticed the brake pedal had to be depressed further in to get the same stopping power. It didnt take too long before the pedal was to the floor and it wasnt stopping. I took it back to the mechanic who told me it was the master cylinder that was out and I needed a new one.


1. Is it possible he screwed up on the installation and it needs to be bled and refilled? (Something he initially suggested)

2. Being in Belize you can't get MG parts they have to be ordered in. Is there another car master cylinder i.e. toyota that can fit a 1978 MGB?

3. Will anyone be coming to Belize any time soon and will be so kind as to pick up a part or two for me smiling smiley?



ingoldsb Avatar
Terry Ingoldsby
Calgary, Alberta, Canada   can
1971 MG MGB

1. Is it possible he screwed up on the installation and it needs to be bled and refilled? (Something he initially suggested)

Not likely. Oftentimes when a master cylinder is near the end of life, almost anything will disturb it. What happens is that the rubber rings that seal the piston normally travel over a certain portion of the cylinder. When you crack open the system (to change lines, or just to bleed it), the piston now moves into a region it didn't normally reach. There is often some corrosion in that area and, as the rubber parts wipe it, it is the straw that breaks the camel's back.

Quote: 2. Being in Belize you can't get MG parts they have to be ordered in. Is there another car master cylinder i.e. toyota that can fit a 1978 MGB?

Not without a great deal of work - definitely not recommended. If your master cylinder is in good shape (not pitted) then, providing you have the skills, you can put in a rebuild kit and should be fine for years. However, people on this BBS keep telling me that it is a hard job. winking smiley You will have to judge your own skills and the internal condition of your m/c.

Terry Ingoldsby

twigworker Avatar
Jack Austin
Blowing Rock, NC, USA   usa
Ajay, you didn't say which "line" was leaking and was replaced but I will suppose that it was one of the flex lines.

Ditto on all that Terry said, but I would add this...

Do yourself a favor and "shotgun" this situation. If one of the flex lines was bad then all three, the other two, should be replaced as a preventive measure.

Also, look carefully at the steel pipes running across the rear axle that carry fluid out to the wheel cylinders. They are often found squashed where a tow truck driver has latched his J-hooks around the axle and pulled them tight. Replacement of the pipes is called for if a problem is found there.

Pull the rear drums and eyeball the wheel cylinders, lining material and axle seals. Pull the cylinder dust boots back a little to check for seepage even if you can see no actual leaks.

Finally, replace the master cylinder. As posted in previous threads, I realize that an effective overhaul can be done, but the liability issue is just too great these days. Replace it with a new one. At the same time look carefully at the clevis between the master cylinder push rod and the hole in the top of the pedal arm. Elongations calls for repair. A new pin will be needed but the push rod itself can be saved by brazing flat washers to both sides of the old rod if you can't get a new one, and the pedal arm can be welded up and re-drilled.

In the brake department it is false economy to short change repairs. Do it right the first time and you can feel safe,


--------------------------------------- Services to Interesting British Automobiles----------------------------------- ----------------------------------------------------

-------------I like to think that I don't service automobiles so much as I provide entertainment, fulfill dreams and revive wonderful memories --------------

I am in the northwestern North Carolina mountains, right up against the Blue Ridge Parkway. Lawn chairs are in the shop and always time to talk. Drop in any time.

BumbleB74 Avatar
William Milholen
Tidewater VA, USA   usa
I wouldn't skimp here either. You life, or somebody else's is worth a WHOLE lot more!

Oh, and drop by more often, even when you don't have a problem!

1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, un-named, Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels

docajay Avatar
ajay h
belize city, Belize   blz
1978 MG MGB
Hey guys,

Once again, thank you all for the great support you have offered. The line that was leaking was the one on the front right wheel, however I went ahead and replaced them all using the "Brake Pipe Set" from moss motors. I am going to go ahead and order the master cylinder, with shipping it is coming out to be about $180.00 from (anyone ever used them before).

Jack thank you taking the time out to guide me through this process.

As soon as the clutch comes in I shall keep you guys posted.

Thank you,


DB Wood Avatar
Daniel Wood
Tumalo, OR, USA   usa
1969 MG MGB GT "Clyde"
1970 MG MGB GT
Although it is best to change the master, I have found that flushing the fluid often will revive a master cylinder as long as it is leaking internally. My Saab 900 had the typical master that would bleed down in hot weather under light pressure. Changed the brake fluid and the problem went away for a year. Changed the fluid again and it is still good a year later. Water in the brake fluid is the cause in some cases. In fact that is the second Saab that I have cured the brake master problem in this way. I have always used Castrol LMA brake fluid in the Saabs and MG's. Others have used many brands but Castrol has never failed me, so why change?

Dan Wood
70BGT driver, OD, Pertronix, HS4's, Peco, .060 over, Elgin cam, Superlite wheels, poly bushings, panhard rod, rear tube shocks, 1" lowered front end, HD shock valves, etc, etc.
68 MGB rebuilt engine D9 cam balanced, still a work in process but runs real nice.
88 Saab SPG Turbo
86 Vanagon Westy (South African conversion engine 2.0 OHC 135HP)

Lucas= Loose

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