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MG MGB Technical - Hard Brake Pedal

Very hard brake pedal on my 72B. I have some ideas, but thought I would ask the "audience". Anyone have some good knowledge on this subject?
James Huggins


Personally, I like a very hard, low-travel brake pedal... but some people don't. Here's one good approach to "softening" the pedal (and simultaneously increasing available braking force at the wheels): http://www.britishv8.org/Articles/Budget-Brake-Mod.htm

Please note the disclaimers. There are many different variables that interact to determine how a brake system performs. Changing to a later model power-brakes system or fitting differently sized cylinders (smaller master cylinder or larger wheel cylinders) might also work.

The article recommends two books on the subject. I've read the Fred Puhn one, and can recommend it. IMHO his "How to Make Your Car Handle" is a classic.

Curtis

James, from your post I'm not sure what you are refering to, is the pedal normally 'hard' or has this happened after some maintenance? Please elaborate a bit.
Bill Young

Hard pedal is good. What is not so good is only being able to lock the front wheels with difficulty. A North American 72, I presume, and so no servo to fail and cause 'difficult to lock'. That leaves problems with the pads and/or discs (the rear brakes add very little retardation). As Bill says we need more info, this can simply happen with new pads, which take time to 'bed in' and give full retardation. This can take much longer if the discs are scored. Does it pull to one side? If so I'd suspect a blockage in the hydraulics on the side it pulls away from, slacken each caliper bleed nipple in turn and make sure you get an equal volume of fluid out each side, and the pedal should go to the floor very easily.
Paul Hunt 2

It just feels very hard with only slight braking. Panic stops are impossible. I don't have a history. I purchased the B for rebuild. So far I have only replaced pads on RF.

My thoughts:

1. bleed all lines, note I do have a mashed flat brake line on LR.
2. I have purchased new MC but have not replaced. On second thought, I didn't think it would do any good.
3. Will update, I am going to check and rework the LF, and both rear brakes, and replace the line.

I have finally reached this point after about 8 months working on this B.
James Huggins

Still not a ton of info to go on, but it sounds like stuck pistons in the calipers/wheel cylinders or obstructions in the lines. A complete brake redo would be in order.
Tom

"I have a mashed flat brake line on LR"

OK, not a lot of info to go by, but if this is not a smoking gun what is!? If the line is closed off, then the fluid displaced by the master will be divided amonst the other three corners. Less fluid to move equals shorter pedal travel.

When you say the wheels won't lock, do you mean front or rear? What pads did you use and have you broken them in? Did you use new rotors. If you re-use the old rotors, chances are the new pads are just riding on the ridges and using very little surface area of the disk. This could improve as the pads are worn down to match the disc.

Good luck with this.

Pete
Pete

One simple thing to check is if the brake switch on the pedal cover under the hood is screwd in to far. This can cause the piston to not move back enough to allow the fluid to fully release easily.
BEC Cunha

My LHD GT V8 is fitted with the pedal box from a 1975 US MG B and dual circit, incorporating a servo.

I have the same system in my 1975 roadster, all hoses and lines are O.K., so are the seals and pads and everything mooves fine. Both the systems are filled with silicone brake fluid and bleaded propperly, the material of the pads is identical and both the servos are working fine. The rotors are in as new condition.

The roadster has perfect braking performance like a modern car with ABS switched off, the GT is hard to stop and it is difficult to have the front wheels blocked. The difference in wight between the cars is not that mutch to explane this differance in breaking performance.

Talking to another MG owner with a GT V8 and a roadster, I was told that his experience was just oposite to mine.

Has anybody an idea where to start investigating the GT's system, it is equal to the rodster's in any aspect but the thicker dics and calipers both with the same seals and the same new pistons...

Ralph
Ralph

HI James,you may have no rear brakes.It is common for the warning valve block to pop in one direction when bleeding.You must centre the valve & lock it in place until brakes are bled.A QUICK CHECK IS TO LIFT THE REAR WHEELS CLEAR OF THE GROUND,APPLY THE BRAKES,IF YOU CAN TURN THE WHEELS THE VALVE HAS POPPED & WILL NEED TO BE RECENTERED.
Mick burke

The brake pressure failure valve on 68 to 74 North American cars turns on the dash light to warn the driver of a problem, but it does "not" shut off brakes. The only seals in the valve are two shuttle seals to keep fluid from leaking into or around the plastic switch. See details of the switch in my Yahoo photos
http://new.photos.yahoo.com/flash1929/album/576460762322215695

Clifton
Clifton Gordon

This thread was discussed between 18/12/2006 and 28/12/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.