Hey Guy,
This thread is going to sound silly but I literally have run out of ideas as to what is causing problems with my brakes.

1987 pickup

A few weeks ago I replaced my rear axle. I hooked my old brake lines up and noticed I have no pressure at the brake pedal. I replaced a ton of brake line, my bleeder valves and the master cylinder and still have the same problem. I can press on the pedal when the truck is off and the pressure is great but once the truck turns on the pressure goes away and won't stop the truck.

I adjusted the brake shoes, gravity bled the lines, got a vacuum pump and bled the entire line out of air but still have the same problem. I disconnected the booster to see the vacuum pressure and the booster works great. It's been 2 weeks of brake work on this truck and still no progress. Any help would be greatly appreciated!!
Thank you

 

I have only been able to successfully bleed the brakes while the truck is running and someone is assisting. Can you use the vacuum pump while the truck is running or get someone to help out?

 

Yea I tried it. There was some air coming out of the line but overall it still wasn't a hard pedal

 

Sounds like a bad mc. Swap it out.

 

I did again last night. I put in a refurbished one and last night I bought a brand spanking new one And put it in. And still no luck

 

Then brake booster.

 

Sounds like you might have the lines to the lspv mixed up
Swap the two lines around and try again

 

X2

Also check the MC. If you got one from Advance/AutoZone, then chances are you got garbage. I live in Roanoke, VA where Advance is HQed, and I HATE their parts

 

I had a refurbished one but went out and decided to buy a brand new one afterwards. I didn't touch any of the lines in the engine bay, only the rear brake line on the axle and the one under the cab going to the MC

Would a squishy pedal be the booster though?

 

what order did you bleed the brakes in?

 

I started with farthest to closest. And after I redid the master cylinder a few times I switched it up to closest to farthest and farthest to closes again. I've been doing these brakes over and over again for 2 weeks and still can't get pressure

 

when you did you bleed the lspv in that sequence? you do know you have to bleed the lspv right?

 

The ISPV being the rear one on the frame? That was deleted And cut off from the previous owner. Or is there another one I am missing?

 

that is the only lspv. How are your lines being ran? One MC port to the front, the other to the rear? Any inline manual proportioning valves installed? Do you have the required residual valves in your mc? factory size calipers/drums?

 

Booster does not effect pedal only the effort to push it.

Your getting air back in the system some place or your rubber brake hoses are swelling up under pressure.

Poor connection will allow air back in.

Then maybe your rear shoes are not adjusted up enough or the drums are worn over size .