brake problem

[zookfest]

have bled the brakes on the 70 and has a hard pedal,the brakes are vacum assist and have a hose for vacum out of alternator to reserve tank with sensor then up into the booster.

truck has near no brakes but when i take the hose off the booster there is a big sigh of release so it is getting vacum to that point

so what am i doing wrong

also its a master cylinder from a 3b and the motor is a 13bt are they at all different

[H2OLOVA]

truck has near no brakes but when i take the hose off the booster there is a big sigh of release so it is getting vacum to that point

I presume its is a vacuum/sucking noise and not a pressure/release noise?? If you can bleed up the brakes and get a good pedal when the trucks not running then i would guess you have issues with the booster. Not to sure how you could test this without trying another booster to see if it makes any difference.

[thommo 1]

you can test the booster. with the engine off pump the brake pedal a few times to purge it and then with your foot hard on the brake pedal start the engine, if the brake pedal sinks slightly the booster is working. if it doesnt, you have and booster or a vacuum problem.