Refurbishing Drum Brakes - Whoa It Down - CHP Step By Step

A brake-spring compressor like this one from OPG (PN CVT0269, $10) makes the off-and-on task easy. The backing plate may look like a simple part, but it supports the drum-brake system and allows the shoes to move correctly. Inspect the contact areas on the backing plate for wear. True Connections offers replacements.

We inspected the rear drums for cracking, scoring, and grooving. Having the brake drums turned to a smooth surface can repair small imperfections, tapering, or out-of-round conditions. A maximum-diameter spec is cast on the outside of each drum. Past this point, braking performance may suffer because the thinner drums will not dissipate braking heat well.

Many GM F-bodies ('82-88), G-bodies ('78-88), and S-10 trucks ('82-88) use this special retainer to hold the rear wheel cylinder in position. Removing the wheel cylinder requires prying up both tangs from the retainer. To install the retainer, we hammered it on with a 111/48-inch 12-point socket. If the clip comes loose, the wheel cylinder can rotate because both top ends of the shoes move uncontrollably outward, resulting in rear-wheel lockup. '77-and-earlier GM cars used a bolt-on wheel cylinder and did not exhibit this problem.

The solution to holding the wheel cylinder firmly against the backing plate (with the retainer) is to install this $15 retrofit bracket from Raybestos (PN GMB25851). This eliminates the chance for rear-wheel lockup due to a rotating wheel cylinder. By using the bracket as a template and drilling two 151/464-inch holes, the bracket secures through the backing plate and into a flange on each side of the rearend with two self-tapping bolts (provided).

If you want to increase the size of your rear-drum system ('64-77 Chevrolet musclecars) for improved stopping, Master Power Brakes offers an 11-inch finned-drum system that is much larger than the stock 911/42-inch setup. Larger drums increase the effective friction area while also improving heat dissipation. This equals comparatively shorter stopping distances.

Before our install, we placed the new actuator lever onto the trailing shoe (secondary) with the lever pivot (A) in place to locate it. Notice how the primary shoe's friction material area (B) is smaller than the secondary shoe's (C). The primary shoe (smaller of the two) always faces forward (like an arrowhead). With the backing plate clean, we also lubed all of the brake-shoe contact areas with a small amount of high-melting-point silicone grease.

We installed all the Raybestos brake parts with the proper tools so that we did not damage any of the hardware. Each backing plate used two hold-down pins to secure the two shoes. These were retained with a hold-down spring and a specially slotted upper washer that was depressed, turned, and released with a brake-spring compressor tool. Next we installed both shoe-return springs, using the brake pliers.

Note that the adjusting-screw spring (arrow) coils are not above the star wheel. If reversed it would have hit the star wheel. Left- and right-side adjusting screws are threaded opposite and do not interchange. This drum-brake adjusting tool (aka spoon) is available from OPG (CVT0272, $7). We adjusted the star wheel downward then test-fit the drum into position, checking for a slight drag. If it is too far down, the pawl, which locks onto the star's cogs, must be lifted up to release the star. Then we installed the drum and adjusted for a slight drag.

The final step was to bleed the system with the rear drums installed. After topping off the master cylinder and installing the cap, we had an assistant slowly pump the brake pedal (parking brake released). After about three easy pumps while holding the pedal down we released the bleeder screw. We repeated this step at each wheel, while monitoring brake-fluid level at the master cylinder, until only a stream of brake fluid flowed from both of the rear-wheel cylinders. Then we topped off the brake fluid again and gently test-drove the car.