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MG MGB Technical - Soft brake Pedal

Hello all,
was wondering if someone can help diagnose a brake problem with my 72 B GT ?
The brakes were spongy, so I bled them and it made a bit of a difference but now the pedal is still very soft on the first application of the pedal. The next press or presses the pedal is pretty firm ...

any ideas pls ?

Jon.
Jon

Sounds like the master cylinder seals are on there way out.
K Harris

I would guess there is still air in them. Bleed them again, preferably with an Eezi bleed system, and see if this improves things. I assume when you bled them you ensured you completely changed the brake fluid (ie got all the old stuff out). If not then also make sure this is done.

Good luck,
Iain
I D Cameron

Thx. can the seals be replaced themselves, or only the whole master cylinder ?
jon

Yes you can replace them, but in practise a new M/C is a easier option as you can have wear in the bore, new ones on EBAY all the time.
K Harris

Have you inspected the braking system for leaks? Was there any work done on the brakes recently? How old are the flexible brake lines?
Kimberly

Definitely check your front brake hoses. If they feel soft change them. It is an easy job and the hoses are not expensive. You might consider up-grading to the braided lines.
Lee

Stick to the simple thing first. By far the most likely thing is that there is air still in the system. Unlikely to be brake hoses as you get a firm pedal on a second pump. If it was hoses you get a spongy feeling on both pumps I think (as pressure of first pump released the hose would return to normal, second pump does the same thing). To test for leak press pedal firmly over a long period (5 -10 minutes). If the pedal goes further and further down then you have a leak, either in the brake system (ie fluid escaping) or in the maste cylinder seals.

Iain
I D Cameron

Sounds like air is still in there to me. This is exactly what I get after bleeding mine (both cars), either with the pedal or an EeziBleed. After the 'normal' bleeding I then have to get someone to stand on the pedal while I rapidly open and shut each caliper nipple in turn. This always gets an extra 'lump' of air out, and after that the pedal is fine. I'm not sure whether it is due to the much higher pressure developed with the nipple initially closed compresses the air bubbles which detaches them from the wall of the pipe, or the sudden extreme flow blasts them of the wall off the pipe, or simply pushes the air bubbles out of the loops of pipe and down to the calipers whereas lower pressure and flow allows them to rise as fast as the fluid flows. But it works for me.
Paul Hunt 2

This thread was discussed between 15/11/2006 and 17/11/2006

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