I have had DOT5 for 27 years in my truck, nothing has deformed yet and I am still waiting for the brakes to explode and fall off.
Go to a parking lot and give the truck three or four good hard stops from 30 to 40 mph. It will help set the shoes to the drums and wear off any edge or rust that maybe grabbing, this will also give you a better idea what may or may not be happening. Take along a thermo heat gun and check drum temps just to see what all four are. Everyone should do this just so you know what the truck is going to do in case you really need to stop. A true problem will repeat itself time after time.
Use a short section of clear bleeder hose, maybe 3" long, just long enough so it points straight up. Open each bleeder just enough to allow fluid out, but not let air enter around the threads, if there is any air, it will be at the top and come out, if no air, all you will get is a little bit of fluid. No need for waisting fluid, a full system will dribble fluid as soon as the bleeder is open. You may need a helper to apply a little pressure since the master cylinder is low mounted. Firewall mounted MC will gravity bleed easy enough. If you feel you need to fully bleed them again, just reuse the fluid if its clean, run it through a paint filter if it makes you feel better, I just dump it back in the master and go on.
Second quick test is to check the toe-in adjustment. Roll the truck forward on smooth ground at least one tire revolution without hitting the brakes. You want it to be in as driving position. Have helper hold one side of the tape measure, pick a tread groove or outer edge, or better yet a scribbled line down the center, and a high up as possible. I know the exhaust or something else will not permit using the half way point, but the higher you can measure, the more accurate it will be. Start at the rear of the tire, then move to the front and use the same points to measure from. 1/8" smaller at the front. This adjustment can cause all kinds of weird driving if its not right.
Tie-rod end adjustment, if they are loose, under hard braking, the spring gets collapsed moving the toe-in to toe-out real fast causing the one side to pull off center. Fully seat the adjusting screw to bottom out the spring, then back off 1/2 to 1 full turn. I went the closest hole that allowed the cotter pin to go through.
Be sure the steering wheel is center to the steering box, and the steering box is dead ahead straight when the tires are straight ahead, the tight spot of the gear box helps hold the steering tight. If the gear box has free play in the gears, it can cause stopping issues as well.
You can always swap tires left and right just to rule them out, it's unlikely they are the issue, but it can't hurt.
My truck will momentarially pull right but self centers and stops OK. I have tried to eliminate it, but it always does it under extreme stopping. My 40 mph jam on the brake test lets me know what to expect, and every so often I repeat it just so I'm reminded of it. Mine stops fine and I don't worry about the quick pull, what I do think about is the rear tires locking up, I have a regulator on the rear brake line to limit the pressure and prevent total lock up. It's set for the worst case stop, its on the edge of total lock up, tires just leave black marks but still roll. I can get total rear lock if I try. My truck has soft leaf springs and nose dives more then a stock spring did, so not much weight on the rear tires when braking. I do have disk brakes up front.
With the rear also acting up, a readjustment sounds like is what you need. Do the parking lot test first so the shoes are seated good, then readjust all four wheels. My method is to adjust till the tire won't turn, then back off 5 or 6 clicks of the star wheel on modern brakes. The '38 manual said to adjust to a slight drag, then back off 4 clicks. Your idea, GM's idea, and mine will differ on what a slight drag is, going to lock up then backing off eliminates the feel aspect.
Joe
