1977 f-150 6 cyl auto

seems all my signal issues cept the obvious damaged fender fixture stem from the brake pedal not fully returning...ie brake lights stay on preventing other signals from working unless i lift the pedal the rest of the way. odd thing is my pedal responds with good pressure and normal return when the motor is off, but I lose ALOT of pressure ie I have to depress the pedal almost to the floor before the brakes engage and I feel any resistance and theres no pressure to return the brake to its original position. the MCs resevoir is full, and the lines all look good....whats going on?

 

Are they power brakes? could be a bad vacum booster

 

how can i tell the difference? my ignorance is massive! but im willing to learn

 

right behind the mastercylinder should be a large round drum. if you have one, then it has power brakes.

 

aha! yep big round black thing behind the MC? yep its powered. ok heres anouther thing.the smaller front resevoir on the MC was empty. I filled it. started up the truck. pressed the pedal bout 10 times, noticed no change in pedal, went back to the MC saw that it was half empty, refilled, pumped again, same results. crawled around under the truck couldnt find any drips....is it backflowing into the vacuum booster?

 

i have heard of this happening

 

 

How does brake fluid from the front (primary circuit) get past the piston seal of the REAR reservoir without emptying it as well ?

The Rear seal of the M/C piston is closer to the booster

 

sorry didn't realize the back wasn't empty as well