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MG MGB Technical - front brakes freezing???

73B' Running fine. Then all of a sudden the front brakes freeze up. Takes about twenty minutes to free wheel front hubs. Already replaced brake lines, polished pistons, new seal kits. Haven't got into the master cylinder yet, but has anyone have a sudden failure happen and is there any suprises that I can possibly avoid?
Victor Gardino

What a pain, did you change the flexi brake line to the calipers? next time it seizes, undo a flexi line on one side at the caliper and see if it frees up the brake on that side, probably will not so then its easiest to swap the caliper, if it does free the brakes then change the flexi lines. Have you adjusted the master cylinder actuating pin at the pedal top, there should be a few mil of free play to allow the fluid in the lines to release back to the cylinder.
Tatty

Is it just the fronts, or the rears too? If they all freeze then it could be a sticky piston in the servo. If so then it's quite easy to remove and clean it - and with care you don't even need to bleed the system afterwards.
Miles Banister

Victor; Since you said both brakes are locking up the only thing common to both is the master
cylinder and pressure failure valve. Sounds like you replaced the hoses. Did the brakes unlock
by waiting or did you do something to unlock them? I just went through the same thing on one
front brake and I found it easier to open a bleeder to see if the caliper unlocked. In my case it
unlocked the brake, the hose was bad. You could also losen the brake line into the hose, if that
unlocks the caliper the hose and caliper should be ok and the trouble is in the master cylinder
or the lines. I don't think the brake failure valve on a 72 can shut off the brakes.

You mentioned you polished the pistons? I have never done that, I replace any pistions that look
bad so I cannot comment on what may happen if the pistons are polished.

Regards, Clifton
Clifton Gordon

Sounds like the master cylinder is not retracting all the way. Sometimes a little crud gets in the way. It only takes a fraction of an inch.
The brakes are heating up and the fluid expands locking the brakes. When the brakes cool down, about 20 min. the brakes release till you start driving again.
Kelly

I have had the same thing on a 74 NA spec B with the brake light switch adjusted in too far and putting slight pressure on the pedal. If your master cylinder pedal box cover is a bit misshapen or not quite correctly installed this happens easily. Try backing out the brake light switch a couple of turns or take the shroud right off temporarily and see what happens.Anthony
Anthony Henderson

This thread was discussed between 12/06/2002 and 15/06/2002

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