Re: Why do my drums lock up??
There is a valve in your brake lines, (usually in the bottom of the master cylinder) that holds pressure against the wheel cylinders to make them keep adjustment.
These valves do go bad at times and hold too much back pressure against the wheel cylinders.
You should only have about 5 psi, and no more than 10 psi in the lines.
It's easy to tell with a gauge, unfortunately, most people don't have a gauge for break line pressure.
If you have done several brake jobs, you can crack the bleeder valve and check for pressure there.
Crud can accumulate in the wheel cylinders, and cause the pistons to drag or stick out.
This is easy to tell, just pop the wheel cylinder apart, and look for crud.
If you shoes are REALLY warn out, the pistons can go out too far, and stick too. (Usually in the crud..)
Some brakes are designed so that they will 'Cam Over' when the pads get so worn that the wheel cylinders are about to come apart.
That will cause the brakes to drag.
Another major cause is neglect. When the shoes are changed, or checked, people don't clean the crud out of the brake mechanical workings, and the acidic brake dust, and the corrosive brake fluid, combined with huge temperature extremes, and maybe good doses of mud, sand, dirt and water, all combine to 'plug up' the workings and cause things to stick.
I've seen emergency brake cables, and actuators get rusted and corroded up so badly that when you apply the brakes, the emergency brake doesn't disengage completely.
On very rare occasions, I've seen proportioning valves and safety valves go bad, but that is so very rare I even hesitate to mention it.
How about smashed brake lines holding pressure against the wheel cylinders...
Lot's of things it could be, maybe you have a better idea of what some of them are now....
Good luck, and keep us posted.
"I Have The Body Of A God... Buddha"