Brake question

What shoes did you have installed? Did you replace the drums? That is going to have a lot to do with how often you have replace them. There may not be anything wrong with the brake system if you reused your drums and installed the cheapest shoes on the market.

 

My first guess would be an air leak. Chock the wheels. Release the brakes. Then turn the engine off so you can hear and have someone hold the pedal down while you check for a leak. Unless it's pulling to the right or left when you stop then it's probably not a problem at the wheels.

 

What do you mean you hear back pressure? I thought you meant you were hearing an air leak when you stepped on the brake.

 

No wear on front brakes could also possibly could be worn out auto slack adjusters in front, s-cam bushings, or bad brake chambers. Brake chambers dont need to spring a leak in order to be bad.

 

Trucks normally have a valve that limits application pressure to the front wheels. The harder the brake application the closer presser becomes equal to the rear. An over the road truck with a operator easy on the brakes can get a million miles on the steer axle shoes.
Hope that explained functions a bit. Sounds like you have some other problem.