The front brakes were working fine, but I had a leak in the brake line back by the rear. I took it in to get the line fixed, and they said that I also needed to replace the master cylinder.. They replaced that, and then they said that the passenger caliper blew a seal during the test drive. The guy working on it is a friend of mine who owns a shop, and he suggested that I just replace the caliper myself to save money on labor since it's a pretty easy job. I did that this morning, and bled both sides of the front brakes. I don't see anymore leaking brake fluid.

During my test drive, it felt like all I had was back brakes. When I try to stop suddenly, the back tires lock up and drag while the front keeps rolling. I don't think the front is getting any pressure, but I'm not sure what else could be wrong?

 

Pickup? With no weight in the bed, it's likely you can lock the rears while the fronts are still braking (rolling).

Have you asked your friend? a) he knows more about your rig than any of us, b) he's the one who installed the (now suspect) master cylinder, and c) he's a professional (does this for a living).

If you want to tackle this by your lonesome, jack up the front and have someone lightly press on the brake pedal. Can you turn either wheel by hand?

 

Yeah, it's a base model 2wd pickup. He mentioned that when he replaced the brake lines up to the proportioning valve, that the valve might have gotten clogged somehow (or be clogged with all the rust that was going through the lines when he was bleeding them). He'll look at it in a couple days, I was initially just looking for opinions to get it resolved today because I hadn't heard back from him yet and I couldn't think of what else it could be. But honestly, I've never even heard of a proportioning valve before, so clearly there is plenty about working on cars that I don't know.

 

The proportioning valve is the last thing to bleed. He should know if it is clogged because if it is clogged the fluid is not coming out of it.

If he fooled around with the proportioning valve, there could be too much rear brake pressure causing lock ups. The proportioning valve system is designed to increase brake pressure to the rear brakes as the loaded weight increases.