Brakes on strike?

[Eddge]

I know bigger tires always puts more of a strain on the brakes, but the brakes would stop the 35s that were on the truck before, now I have 38s and the truck doesnt like to stop now. The brakes work but I have to pump them a few times every time I go to stop. I have bleed the brakes a few times, and I know I am bleeding them correctly, but I always have to pump the brakes to get them to work. Any ideas? I have not been able to find any leaks either.
It is a 77 F150 4x4.

 

[johnny reb]

I know bigger tires always puts more of a strain on the brakes, but the brakes would stop the 35s that were on the truck before, now I have 38s and the truck doesnt like to stop now. The brakes work but I have to pump them a few times every time I go to stop. I have bleed the brakes a few times, and I know I am bleeding them correctly, but I always have to pump the brakes to get them to work. Any ideas? I have not been able to find any leaks either.
It is a 77 F150 4x4.

Have you checked for a leak under the dash-sometimes the master cylinder will leak behiond it and the fluid MIGHT be leaking inside. Also check the check valve going into the brake booster. Sometimes the leak is behind the line on the frame side. Also-when you bleed the brakes------do you get air again ? If so-air is re-entering the line. Double check the line really good--go over ALL OF IT. Look at the firewall where the brake booster mounts up for brake fluid'
Good luck

 

[johnny reb]

I would watch the fluid leve and also check behind the master cyclinder for fluid.You might also want to check under the carpet on the driver-side of the carpet. Also,get under the truck and check under the line on the inside of the frame.Take a light and look-it will help you spot a leak better.A little pin hole can cause you to get air back into the lines.These a a few plaxes to check for leaks and also check the valve that gores into the master cylinder booster and check for a vacuum leak.Old vacuum lines get bad.Good luck and let us know-ok.