Need good brakes for offroad

[71HANKER]

I have a 71 f100 that has had alot of mods done to it. It has disc brakes up front and drum in the back. it was originally manual brakes but i put a new brake booster that my brother in law had, its for a 1980 bronco, a good used master cylinder off of a 71 ford, with power brakes. The brakes work pretty good, but the pedal is effortless to push. The booster pumps up good with the engine off and doesn't seem to be defective. i have bled the brakes numerous times with a hand held vacuum bleeder and the level is good. i dont know if the proportioning valve is the problem or what. I have 38 inch tires on this beast and i need it to stop. im pulling my hair out. any advice would be great.

[Wes]

the brake actuator rod is in diff positions depending on power or manual. If you have the rod in the same hole as the manual setup, you may have to much mechanical advantage, ( a big lever ). If you can compare your brake pedal to factory power brake pedal.

[heep70]

Do you have the right MC? Calapers take alot more fluid. Also try a 3/4 or 1ton MC. The bores are generaly bigger and will push more fluid.

[71HANKER]

I really appreciate everybodys input. I finally figured out why my truck didn't want to stop. THERE WERE NO DAMN DRUMS ON THE REAR!!!!!!! This truck was an unfinished project when it was given to me and the last owner couldn't remember where he had left off. The truck sat for 10 years in his driveway and he lost interest. I went down to the junkyard and pulled a set of almost brand new rear drums off of a late 90's f150, put them on, rebled the brakes and it stops on a dime! Even with 38's. I did put a new master cylinder on it to, for a 1 ton with power brakes. my 71 has a 460 big block, 79 bronco front axle, with disc brakes, Currie 9'' rear end with 5.13 gears, mickey thompson 38.5 baja claws, c6 trans, and now power brakes. this thing stops better than my 93 chevy!