brake lock

[TnTom]

first time post for me, i have a 77 124 spider went thru calipers & re sealed, ft & rear. took master cyl off -clean & free, it seems to start to lock up after car has been idling for a while if i crack fitting @ master it relieves it and things are normal for a while . could it be the booster? no vacuum leaks there, and i hear the hiss when stepping on the pedal . any help will be appreciated thanks . Tom

[mbouse]

Tom,

Welcome to the site. please take some time to pop up to the introductions section and tell us more about you and your '77... perhaps add some pictures? of the car, not you! har har har..

yeah, the pressure builds and builds, plus a hissing noise? could be the booster. is the check valve in place and properly sealing?

what fitting are you cracking at the master cylinder?

are all four wheels locking, or just one corner?

[So Cal Mark]

I've never heard of brakes locking while sitting, unless a line is in contact with the exhaust and the fluid is being superheated. If you suspect the booster, merely disconnect the vacuum hose to it and see if the lockup still occurs