Power Brake Booster for '68 Super Bee

[Hannibal1340]

Installed Power Brake Booster with new master cylinder part of unit from Classic Industries (part #MB850200). Mechanic says front brakes work fine...rear brakes not engaging. Would appreciate any insight any of you could offer? It's a 383 4-spd with 11 inch drum brakes.
Thank you.

 

[Hannibal1340]

Thank you.

 

[Fran Blacker]

Doesn't engage? Meaning shoes don't move? If so what is in the line from MC to wheel cylinders, brake block on frame rail below MC. Anything else like proportioning valve.

 

[PurpleBeeper]

Sounds like the proportioning valve, or more likely, the rear brake hood off valve is stuck