20 November 2008
 

Brakes Maintenance

Drum Brakes Servicing
 

By : Pierre Lalonde
 

Although disk brakes are increasing in use on the rear axle of many vehicles, drum brakes are still
prevalent.

For example, the 2005 Chevrolet 1/2-ton Silverado/GMC Sierra has switched to rear wheel drive and rear drum brakes. In general, drum brake shoes last longer than disc brakes pads. On most RWD vehicles, the rear shoes should last through two sets of brake pads, while on FWD vehicles you may replace three to  four sets of pads before you replace the rear shoes. This is due to brake balance: 80/20 on FWD vehicles and 60/40 RWD vehicles.

Shoe contact pointers

When servicing and replacing rear brake components, it is important that the repair is done thoroughly. When performing a rear brake inspection, make sure that the shoe’s friction contact is parallel to the  friction surface of the drum. correct mating of the brake shoe and drum will provide optimum rear braking performance.

A simple test

The following test will help you determine the rear brake shoe to drum contact area. Remove the drum, inspect and measure the inside diameter. Also make sure the drum is of sound integrity. With the use of a marking pen, draw a series of Xs across the surface and width of the friction material on both shoes and on both sides of the vehicle. Next, take the vehicle for a road test and perform a series of stops in a normal manner (no panic stops).

Back in the shop, re-inspect the rear linings and you will be able to clearly see the remaining Xs or black marking where the lining fails to contact the drum. The Xs that are erased are clearly making contact. This quick test will also help you determine if the wheel cylinders are sticking under light pedal pressure, if the shoes are sticking on the mounting pads of the backing plate, or other instances that are preventing equal side to side and front to rear shoe contact.

Backing plate check

When servicing rear shoes, check for any wear on the backing plate, because a worn out plate may cause poor shoe return and also wheel lock-up. When new brake shoes are installed, make sure you lubricate  the shoe contact area on the backing plate with high temperature silicone.

New shoes and new hardware go together, so do not reinstall old return springs. With time, they lose their tension and become weak, causing a poor brake shoe return. The wheel cylinders are part of the brake inspection and should be checked for leaks and proper operation. Finally, check parking brake function and adjust the rear shoes as recommended by the manufacturer.