1989 F-150 rear drum brake problem

Of course, I’m only assuming that it’s a brake problem.

The other day I’m tooling about doing stuff when I notice smoke and burning brake smell from my rear wheels. Along side the road I craw under the truck, burn myself on the tail pipe and see that smoke is coming from both rear wheels out of the drums. As I limp home I notice that it seems that both rear wheels are locking up. Not enough to stop the truck, but enough that I have to consistently give more gas to keep moving. Once home, I check the fluid (it’s full and fine), and look for leaks (nothing there). I pulled first the driver side tire and drum and have my wife apply the brakes. They expand and contract normally. Same with applying the parking brake. I did the same with the passenger side. Also no problem. For a day it seemed the problem went away. Yesterday the same thing happend again, except for burning myself on the tail pipe. I’ve asked several real mechanics, several back yard mechanics, and prayed to God for an ephiphiny. The answers I’ve recieved have ranged from a master cylinder (which I think might be most logical), to “when’s the last time you had a certified engine tune up?” (that one came from a local mechanics shop, I definately won’t be going there for any work). I don’t think it’s a rear end problem as when they go that’s it, and there’s no going at all. Before I go out and buy a complete brake system can anyone give me an intelligent solution to this problem?

When you lifted up the rear end and spun the wheels (before you pulled the drums) did they seem to drag? If so I would suspect the parking brake mechanism is not moving freely enough, even though it does move some. If the wheels didn’t drag (awhile after driving) then I think the master cylinder is causing a pressure buildup. The proportioning valves tend to favor the rear brakes with light brake application, so that’s why the fronts aren’t dragging too. If that’s the original 19 year old master cylinder I would certainly change it first. In fact I would change the master first anyway. Do you change your brake fluid every 2-3 years.

I have no idea if it’s the original master, but I would wager that it is. As to wether or not the wheels spun afer I jacked it up, they didn’t, I could definately tell that the pads were agains the drums. It was hot as hell, and I had to use a piece of wood to get the drums off. After everything cooled the drums slipped right on without problem. The parking brake is never used, although I did check and test it after this mishap, so I don’t think that it could be hanging up or not moving freely enough. There seems to be no problem with the front disc brakes.

You could loosen a bleed screw when they’re locked up to confirm that it’s a pressure buildup. Fluid would spurt out and the brakes would let go. The rubber seals in the master cylinder could be deforming when hot and keeping the fluid from returning to the reservoir.

At least check for gear lubricant in the differential housing. Your wheel bearings could be shot.

As odd as it sounds, if the rear end leaks gear oil out the axle seals onto the brakes, they will STICK! But, I think that the rear brake hoses have deteriorated internally and aren’t letting the brake fluid pressure return to zero after the brake pedal is released.
A theory is: the moisture in the brake fluid at the wheel is turning to steam when the brakes get hot enough. The steam pressure then pushes the brake shoes into contact with the drums. Drain all the brake fluid at the wheels and master cylinder, and replace with new.

I’ve checked the rear differential and that’s ok. I put some oil in, but it really wasn’t low. When I pulled the wheels and drum I didn’t see any oil in or amongst the brakes. I’ll be changing the master today and we’ll see how that goes. Of course, that means I’ll be draining the brake fluid as part of the process.

Is it possible for both wheel bearings go out at the same time?

With the brake drums on, loosen a bleed screw. As someone presses the brake pedal, observe the brake fluid issuing from the bleed screw. The brake fluid should come out in a small, steady, stream. If it doesn’t, there is a restriction in the hose or line.

Thanks for the replies everyone.
I’ve replaced the master cylinder, and of course, the brake fluid. Took her for a nice test run giving the brakes a nice work out. The problem seems to be solved. No smoke, no locking rear tires. Now the wife wants me to fix the AC. I told her to open the windows. Not the reply she was looking for. Man, I tell ya…

Thanks for getting back with us. It’s so rare that people on this forum follow up with the solution.