Rear Brake Drum
Brake drums play a very important role in the overall performance of your vehicles
entire braking system. In this article we will explain what a brake drum is, what
it does and hopefully everything else you will need to know about them.
Brake drums are usually found on the rear of vehicles, but prior to the late
60’s and early 70’s they were standard equipment as the
as well. Brake drums are the friction point where the brake shoes contact to slow
a vehicle. They vary in size depending on the application: large work trucks will
use a larger drum brake, while passenger cars use a much smaller brake. Brake drums
can be made of different materials such as cast iron, on some vehicles they have
used aluminum to save weight and improve the cooling of the brakes.
Brake drums are usually stamped with a “maximum diameter” measurement somewhere
on the drum for safety and performance purposes. This must be checked when
replacing the shoes
and the drum requires machining. If the drum diameter gets too large, the friction
surface becomes too thin and can distort or become overheated very easily which
can cause brake “fade” or brake loss. Another issue that may arise if the drum diameter
gets too large is rear brake lock up. This will occur when the diameter of the drum
is so large that too much of the brake shoe is contacting the friction surface,
causing them to grab or lock up when the brakes are applied.
Brake drums are also the emergency
on most vehicles (with rear drum brakes). When the emergency brake is
pulled (lever) or pushed (pedal), it uses a mechanical linkage and cable system
to force the brake shoes out against the brake drums, holding the vehicle in place.
Most vehicles with
rear disc brakes
have the inside of the rear rotor machined like a small brake
drum, with a small set of shoes for the emergency brake.
Brake drums also come in a wide variety of price ranges. Less expensive drums
tend to be made of lower quality materials and may not perform as well. When the
material is too soft, it can cause the drum to become oblong (egg-shaped) which
will cause a pulsation in the brake pedal. Lower quality material may also not work
as well with the brake shoe material causing excessive pedal effort and possibly
noise from the brakes. It is always a good idea to use high quality OEM (Original
Equipment Manufacturer) parts to get the most out of your brakes and avoid problems
later down the road. As with any automotive repair, proper protective clothing and
equipment should be used at all times.
When replacing a brake drum, it must be cleaned very thoroughly of all foreign
coatings. Brake drums are coated after they are manufactured to prevent rust on
the mating surface, this coating must be removed before installation or it will
contaminate the brake shoes and cause performance issues or noise in the brakes.
To clean any brake parts or mating surfaces, you can use an aerosol brake parts
cleaner and a clean rag. Wear eye protection when using spray cleaners, they can
spray back into your eyes and cause damage.
If further assistance is needed, our certified car repair technicians are ready
to answer your car questions
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Article first published 2016-02-03