1968 Other Chevrolet Models

LEFTIE224

MEMBER
1968 CHEVROLET

1968 Other Chevrolet Models V8 Two Wheel Drive Manual

Hello, Just replaced master brake cylinder on 68 chevy dump truck, C60. Its been parked for 2 years after loosing brake pedal. The master cylinder bolts to a vacumn tank. I bled the master cylinder, yet have no pedal. Pedal is somewhat firm, but slowly goes down. I figure I need to bleed each wheel, but that vacumn tank is my cocern. It whines when brakes are applied, and when engine runs, the pedal becomes worthless with no firmness as it has when engine is not on. What does that vacumn tank do, and how does it effect the brakes operations. Thanks

1 Reply

KLSHIEL

MECHANIC
163 POSTS

The vacuume tank takes vacuume from the intake of the engine and uses it to increase the pressure applied to the plunger in the master cylinder when the brakes are applied (It basicly makes your foot heavier). The pedal should be easier to push with the engine running as opposed to off. I would start by bleeding all four wheels stating at the furthest wheel from the master cylinder. The whining in the vacuume tank could be air moving around or leaking, but it could also be that new master cylider leaking. A leaking vacuume tank would make the peddal harder not softer. A leaking master cylinder, a leak any where in the lines, or a leak at the brakes will cause the peddal to drop slowly after being firm. Air in the lines makes the peddal feel squishy or low.