brake question
 

71 swb, front disc, rear drum. when i apply my brake alittle hard the rear tires lock up first, is this common with the drum, disc set up? all my pads are new and so is my master cylinder, other than the rear tire locking up first my brakes feel and work great. just wondering if a new proportionary valve will solve this? are should i just not tinker with.

You might have the rears adjusted a little too tight. I can lock the rears up in both mine real easy.

I ran my back brakes loosely adjusted just so they would come in real late. You might try and use top quality pads up front, it might help them grab more. These trucks are just too light in the back empty. you could also put an adjust prop valve instead of reg, that way when empty you can use little back brakes, then when towing dial some more in.

Could you have a rear "wheel cylinder" or "axle seal" leaking? That would cause fluid to get on the shoe. I would pull a drum and check for something leaking.

I agree with lolife99 about a wheel cylinder leaking inside on the brake components. That has happened to me a few times with the same symptoms you have.Another thing to try is to re adjust the rear brakes . Jack up the rear with both tires off of the ground. Spin the tires and adjust till they start to drag, then they are adjusted.