I installed a complete 4 wheel disc brake conversion system on my 69, including master, booster, proportioning valve and lines. I am having a problem with the front calipers locking and not releasing until I release the pressure out of either of the front bleeder valves whenever I do any hard braking. Under normal braking conditions it doesn't happen. what could be the problem?

It may be the pushrod for the master cyl is slightly too long. If they are locked and you loosen the master from the booster and they release I would shorten the pushrod.

TTFN
Mat

Ya thats probly it, put a couple of washers between the booster and master then try it. Be sure the push rod from the pedel to the booster is not to long first, it should fit without actualy moving the booster interworkings and still return to its stop/light switch.

thanks, I'll give it a try!