[Thanos]

Hey guys, its me! I got my truck going again (added a 750 holley and it moves again!). My brakes were soft before it died two months ago, but they are even worse now. I have put on new front disc pads, a new master cylinder, and bleed them about 5 times. I dont seem to be building pressure up. I am getting vaccumm at the brake power booster. No matter how many times i pump the brakes, it just goes to the ground. I am not losing any fluid.
Ideas and wild guesses are appreciated!

 

[Preston_USA1]

I'm super close to putting a 4 barrel on myself, how's the power now? Anyhow about the brake issue. I am guessing that you did a bench bleed of the master cylinder itself, if not you most likely have air in there. Sometimes air gets trapped in the distribution block and you need to pump it up and try to blast it out. Finally, do not be surprized if you have a bad new master, the one you got is most likely rebuilt and all it takes is a crumb or shaving in there to keep the piston from sealing and you are doomed. (I've had it happen to me) If the pedal feels spongy then its most likey air. If it has even pressure and slowly goes to the floor I'd guess bad master.

Hope it helps, good luck,

Preston

 

[K.C.]

If you didn't bench bleed ( prime ) the new one, you could try loosening the brake lines that go into the master cylinder slightly while someone is pumping the brake pedal. Hold a rag there to catch the fluid. If there is an airlock in the cylinder (fluid isn't getting in there from the reservoir) this may help to get things started.

 

[Thanos]

I have just been around the block with (the brakes scare me) but it seems to have a bunch more get up and go! i went from a holley 600 to the 750.
I bench bled it...

Proportioning valve? I didnt even know i had one on the truck. any idea where it is located on the 80TD? I might replace it too. about the only thing i havent replaced.

 

[MudFlap]

On my '79, it's on the driver's side inside the frame under the cab, just aft of where the frame bends down under the cab. Follow your brake lines from the master cyl, you'll find it.