Very sorry that I overlooked this for so long. Did you solve the problem? A locked-up drum is not uncommon. If you raise the tires off the ground and shift to neutral, (or with your drive shaft removed), you're likely to find you can spin one wheel by hand but not the other one.
The first thing to suspect is a rusted parking brake cable that doesn't get used very often, but now got applied or bumped. Most of the time that will cause a rear drum brake to self-energize going forward, but they tend to want to release in reverse. Once the drum is removed, which won't be easy, you can identify this cause by looking where the two shoes rest on the large anchor pin on top. If either one is not touching that pin, suspect the parking brake cable. Regardless of whether the shoes are fully retracted or not, look at the parking brake strut bar that connects between the center of the two shoes and sits right above the axle flange. You must be able to push that bar forward with your thumb against the anti-rattle spring pressure. It should move a good 1/8". If it is tight and can't be moved, that indicates the parking brake cable is holding it applied. The most common symptom for that is that brake will lock up very easily under light brake pedal pressure.
Less commonly there can be grooves worn into the six "lands" or raised spots on the backing plate that the shoes ride on. Those are caused partly by failure to lubricate them with high-temperature brake grease during routine service. A shoe can catch on one of those grooves and stay in contact with the drum. This is more common on GM products because it's just the edge of the shoe's frame that rides on those lands. The shoes on other car brands have metal tabs formed on the sides of the shoe frames that provide a larger sliding surface so there's little chance of the metal frame getting caught.
One of the advantages of drum brakes is they are "self energizing", meaning one in contact with a rotating drum applies the other shoe so it also grabs even though you're not pushing harder on the brake pedal. (That's why we didn't NEED power brakes until front disc brakes showed up). With a parking brake cable stuck partially applied, that self energizing can cause a brake to apply any time the drum and wheel tries to rotate. The clue is if you irritate it enough, you'll get the wheel to turn a little before it locks up again, and there won't be much noise associated with it locking up.
When a vehicle sits for a long time, as in a month or more, without being driven, the shoes can rust to the drum. There are metal chips in the linings for heat dissipation and those are what rusts to the drum. Suspect that if you see the wheel turn just a little when you switch between forward and reverse, or when you go one way, you see the wheel bounce back and forth a little.
When a vehicle sits for a really long time, as in years, the drum's "labyrinth seal" can rust to the backing plate. The labyrinth seal is the groove on the drum's outer circumference where the lip of the backing plate sits in. Rust that normally builds up in that groove is ground away harmlessly during normal driving, and you won't hear it, but if it sits long enough, especially in wet grass, that can cause a locked brake. The clue to that is you won't see the bouncing like you would with a locked parking brake. The wheel will be solid as though it was welded to the axle housing. To fix that you have to pound the drum off, and the backing plate usually crumbles from rust or it gets bent or torn apart.
By far the last thing to suspect is the differential and axle assembly. You would have had plenty of warning ahead of time in the form of growling or humming noises, then crunching noises. That is pretty rare.
Tuesday, November 25th, 2014 AT 11:20 PM