MGB & GT Forum

Hi all, I’ve an issue with my brakes that I haven’t found answered yet I don’t think. While driving, I can depress the brake, begin slowing and everything works fine. Then, about halfway down the bake pedal travel, I hear a “ppfffttt” and a slight release of tension, then the brake pedal extends a bit further while stopping the car. The final bit of travel usually causes a slight grab of the brakes to stop more suddenly. I’ve bled the brakes several times. I just found a very slight leak (a drip) by the passenger rear brake rubber hose. I plan to tighten and or replace. I’ve checked the vacuum hose from the engine to the booster and that seems fine. Is it a master cylinder, booster or something else? Any help is appreciated!

I have no personal experience with brake boosters*), but changes in backpressure on the brake pedal are often associated with such booster systems.
Normally this release of tension is experienced while with the pedal pushed in, the B is started: then the slight pressure release is considered OK

Of course the brake hose leakage should be remedied first and renewing rubber hoses in anything carb related never does harm anything. I remember visually perfect hoses from my HIF's to the PCV Y-piece had become poreous over the years and this influenced gas mixture and block underpressure
The same kind of underpressure your brake booster is supposed to work with.....

*) PS Once a roommate of me at the office in the seventies and owning a MGCGT told me he had problems with is doubled set of Girling brake boosters. Still I do not know whether such more tricky Girling types were also found on the B. Clausagher's book covers only the B, V8 included and a book of mine covering the A, B and the C does not contain so many details as Clausager does over the model years. Maybe somebody else on MGE knows..




Edited 1 time(s). Last edit at 2024-04-21 10:39 AM by Donthuis.

Chris, So does the brake failure warning light come on when this happened or happens?

I think you’re right. I will replace all hoses plus tighten that leak at the back. I also noticed the vacuum hose into the booster is loose right so I will try that first. New boosters are expensive!

No, but I have a sneaky suspicion it may be broken. When bleeding, I read to loosen the Pressure Differential sensor 3 1/2 turns. So, when I went to do so, it fell off. It looks like it had been that way for a long time. The lead wasn’t attached at all. The plunger wasn’t inserted? But no leak/liquid anywhere on the MC.

Ok, I just tried to tighten the rear leak and was hoping it was at the rubber hose. Alas, nope. It looks like it is coming out of the top of the metal, picture attached. I think I was tightening it, but when a pumped the brakes, it looked like I either did nothing or loosened it. Is the only way to check to drain the brake fluid, take it off and reseat it? What if it still leaks? As always, your expertise for this novice is much appreciated.

Personally, while it will make a mess, I would back the fitting all the way off and then try to reseat it. Wiggle the fitting around as you are turning it on, these fitting can be very finicky. If you are lucky this will solve it and it will tighten down. If it does not go back on and seat correctly you will need to check the threads on both the rubber hose on the tube fitting. Then replace the one that is stripped, hopefully the rubber hose…

At the risk of sounding independently wealthy, brake parts may seem expensive, but they are way cheaper than body shop prices, if the brakes don't brake. I think they're the most important system on the car.
Don't be afraid to replace what is questionable. And don't be afraid to ask questions. You may get differing opinions, especially about bleeding, but you won't find out unless you ask.
The University Motors/John Twist website is an excellent resource.
Good luck

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The important thing is not to get ahead, but to get along.

One advice on this joint for getting the best alignment between the hose end and the metal line end is to leave the nut holding the hose to the pedestal slightly loose in the beginning. This way the danger of having both parts not meeting straight on is minimized. Once the metal part on top is firmly torqued up with a two spanner method to assure no force is exerted on the pedestal this nut above the pedestal can be tightened without risks. Success!

PS Was the metal on the hose end without grooves on top? Such damages influence the mating to the flare on the metal line. Of course renewing the hose will give you a new, unblemished surface to work with. Improving a flare is nigh impossible IMHO, I am not aware of any tool that improves its inner surface.




Edited 1 time(s). Last edit at 2024-04-23 03:59 PM by Donthuis.