There are many reasons for hot brakes

Question:

We have a 1970 Chrysler 300 with a 440 cid engine. We had the brakes and all of the parts involved replaced but even when we drive it less than a mile or so the rear brakes get all heated up and emit smoke. They get so hot that you can’t touch the outside of the rear wheel. What do you think the problem is?

Answer:

It’s almost certain that the rear brakes are constantly applied. This can be caused by a number of different things. Start with the easiest possible problem, which is incorrectly adjusted rear shoes. The shoes should be adjusted so there is slight clearance (about .010-inch) between the linings and the drum.

Another possible cause for the brake drag is that some of the new parts that were installed are not correct for your car. For example, if the brake shoes are too large or if the linings are too thick or if the drums are too small, the brakes will drag. This illustrates why it is so important to compare all of the new parts with all of the old parts to help guard against installation of incorrect components.

It’s also possible that all of the new parts are correct but something was installed incorrectly. For example, there’s usually a forward and a rearward shoe for each side, with the shoe that has a larger lining mounting toward the rear of the car.

The brakes on your car are self-adjusting. A link, cable, and return spring act together to index the star wheel adjustor when the brakes are applied while the car is going in reverse. If the self-adjustor is not working properly, for example, because some of the parts are not installed correctly, it could result in brake drag.

An incorrect or malfunctioning master cylinder could cause rear brake drag. A pinch or other obstruction in a line or hose also could cause brake drag. When the pedal is applied it may provide enough pressure for the fluid to get past the obstruction and activate the brakes but when the pedal is released the fluid may not be able to get past the obstruction to flow back and relieve all of the pressure, leaving the brakes partially applied.

The park brake in your car operates at the rear wheels by virtue of a cable-activated link that expands the shoes. If the system is poorly adjusted or if the cable or some other parts are binding, the park brake may remain on even after you have tried to release it.