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MG MGB Technical - Brakes, or lack there of

Help, I am getting very frustrated with my car. 1973 MGB dual line, non-servo brakes. I asked a few weeks ago about a replacement for a master cylinder, so I decided to order a new one from LBCarco.

To recap, front brake lines started leaking somewhere, checked connections, nothing, but the line was wet. I replaced the front lines. So far so, good, only when I hit the brakes gradually the pedal slowly goes to the floor without really stopping. However if I stab the brakes the car squealed (sp) to a stop. Okay figured master cylinder, so I replaced it today.

Went ahead and attempted to bleed the brakes with a friend that has helped me bleed the brakes before.
I first put the MC in without the lines connected and put in a little fluid and pumped until the fluid came out of the fittings (to prime the MC). I then hooked up lines and proceeded to bleed like normal, only something was not quite right. I had to depress the pedal about two inches to get it to brake. I don't think this seems right but I tested it around our block. I could lock up the brakes, but it took an incredible amount of pedal effort and that is when the brake warning light came on. I figured that I had not bled them the right way, so I tried again.

For some reason when bleeding back brakes the pressure goes down and does not return? Could the rear brake adjuster affect this? Any other ideas?

Thank you
(I have posted this to the email list as well, so I apologize if you have already read my note)
Zach

Zach, first the rear brakes do need to be adjusted.
If they're a little bit loose, the pedal will
be noticeably lower. It's best to use the
correct adjusting tool from Moss or VB, but a
wrench will do. Takes some practice to do this
right -- follow the procedure in Haynes or check
the archives too.

Have you checked the rear brake cylinders for
leaks? The leak may be barely noticeable, e.g.
the rubber boot may be a little moist, but this
is enough to let lots of air into the system.

I've found that a leaking rear cylinder causes
symptoms that mimic a bad MC.
Ronald

Zach-
If it takes "an incredible amount of pedal effort" to lock up the brakes, then you've most likely still got a lot of air somewhere in the system. You said that the "front brake lines started leaking somewhere, checked connections, nothing, but the line was wet". Ask yourself "Which line?" Metal line from the master cylinder? Rubber line to the caliper? How did you "check the line"? Clean it dry with carburetor or brake cleaner, then drive, then look by slowly wiping with a dry paper towel, starting at the connections. Once you've isolated and fixed the source of the leak, rebleed the system until no bubbles and clear fluid comes through. If the pedal pressure problem reoccurs, then you've almost certainly got a bad seal somewhere, most likely in the calipers or possibly the rear brake slave cylinders.
Steve S.

When you did the bleeding did you loosen the fitting on the brake pressure failure switch first? What order did you bleed the brakes? Sounds like you still have air in them somewhere. I've read that it helps to raise the rear end when bleeding.
william fox

Thank you to all that replied.

Ronald - I have no checked the rear cylinders yet because the PO told me that he had rebuilt all the brakes (I know for a fact that the front brakes were replaced when I took the front end apart, so I was trusting him on the rear + he gave me the 'orginal' parts). But I will check again this evening when I raise the rear end up.

Steve S. - I forgot to mention that I replaced all of the flexible lines about two months ago. The reason that I knew that it was one of the front lines was because the crossmember was only wet there, there was a puddle under the crossmember, and when I went to pull out the front brake line for the passenger side it basically crumbled in my hand.

William - Is the switch that wire leading into the 'brake block' (not sure of appropriate name)? I have not loosened this before when bleeding brakes and did not realize that it need to be done, however I will try it now.

Thanks again.
Zach

About that brake adjuster tool.... there is a 4 way wrench with different square holes at each end that is used for opening residential & commercial water valves that do not have the handwheel on them. I can't remember the official name of the thing but I keep a couple around for the stray faucet that doesn't have a handwheel and for adjusting the brakes. It fits the hand and the job better and costs less. Most plumbing supply places have them.
David

Zach,
The switch you are refering to is for the brake lamp warning light. The unit seperates the front and rear brake systems. In side is a sealed rod that slides back and forth with the brake pressure. IE if there is no rear pressure it moves towards the rear and the light goes on. It has stops, so it will not go too far and leak fluid from one side to the other. There is a slot in the top of the rod that will push the switch up if the pressures are not equal. Fluid should not leak from this fitting, even with the switch removed. If it does you will have problems.
As for your brakes not working well, I would think you have air in the system. I always start at the rear drivers side(longest line) and work to the shortest, front drivers side. An old trick to assure no air is to connect a rubber hose to the nipple and place it in a glass jar with some fliud in it. Open the nipple and as you pump you will see air bubbles in the fluid at first and you can stop when the fluid is clear. As the hose is in fluid no air can be sucked into the system as you close the nipple.
The rear brake adjustment is fairly easy too. Jack up the rear of the car and in neutral with the handbrake off spin the wheel. You tighten the adjuster one notch at a time whike spinning and when it starts to grab, back it off one. Make sure the wheel spins free as you don't want it catching.
If you have no leaks and bleed the system you should have good brake if the calipers/cylinders are working. Also, sometimes you have to pump like hell to get the fluid started on the rear.

Hope this helps
john
J Arthurs

Thank you for the responses. I think that I have everything figured out at this point. The switch was for some loose for some reason.
As some had mentioned I let it sit over night to let it 'gravity bleed.' Well when I went to check it the next morning, there was pedal pressure and the light no longer came on. The brakes feel ok, but I really don't have anything to compare to.

Zach

This thread was discussed between 31/08/2002 and 05/09/2002

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