Professionals run into cars every week that we have never seen before. The secret is to take just one side apart first so you can look at the other side.
There can be different brake system designs on the same car model and year, but what you need to look at is how they are adjusted. If you have a fixed anchor at the bottom of the backing plate, the front and rear shoes will be the same and interchangeable. It sounds like you have a star-wheel adjuster at the bottom connecting the two shoes together. That is a movable anchor. That is called a "duo-servo" drum brake. On those, the shoe toward the front of the car is always the smaller lining. That is the primary shoe. Its job is to grab onto the rotating drum and try to rotate with it. In so doing, it pushes on the star-wheel assembly which pushes the bottom of the rear shoe into the drum. At the same time, the piston in the wheel cylinder pushes the top of the rear shoe into the drum, hence, due-servo. Two forces are acting on the rear, or secondary shoe. The rear shoe does most of the stopping. That is why that lining will be longer and/or thicker.
You also need to coat the six "lands" with high-temperature brake grease. Those are the three raised spots on the backing plate each shoe rides on. Chrysler uses bent-over tabs on the shoe frames for those sliding surfaces, so there is no wear, but GM does not bother with that or care about it. The edges of the shoe frames will rub grooves into the backing plates and the shoes can catch on them. That can cause them to not apply under light pedal pressure, and not release at times. Using that special brake grease is the only thing you can do to reduce that wear.
The drums need to be measured to insure they are still within the manufacturer's published legal limit for diameter. You do not want to get caught with over-size drums after a crash caused by the other guy running a red light. A lawyer or insurance investigator will convince a jury you were partly at fault for the crash because you were less able to avoid it. If the drums will still be legal after they are machined, the people at most auto parts stores will do that for you. Before mounting them on the lathe, they should scrape off the one or three round rust spots on the mounting surface. Those correspond to holes in the hub where water can sneak in. If you do not clean off that rust, they can get stuck between the drum and hub and prevent it from sitting squarely. That will make a horrendous wobble in the drum and wheel.
To maintain the front-to-rear brake balance that was carefully designed in, you should replace the return springs on the shoes. They come in a kit that is very inexpensive. The heat from braking makes those springs lose some of their tension, then the rear shoes can apply too easily and lead to easy rear-wheel lockup. A lot of us do not replace those springs, but it depends on the quality of the job you want to achieve.
Thursday, November 12th, 2015 AT 9:39 PM