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Rear Drum Brake Diagnosis | How to repair pesky brake problems.

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This particular weekend started with a call from a pal who had a vexing problem. His usually trustworthy and freewheeling Toyota pickup truck had rear wheels that refused to turn. The pickup truck was a basic Eighties model with even more basic drum brakes out back. Running through possible problems and finding solutions is what we were going to do on this given Saturday. Freeing the rear wheels to return to their usually rolling selves should be basic, or so we thought.

Big Turnout
Drum brakes feature a set of shoes that get pushed out by a hydraulic wheel cylinder against a drum. A set of springs returns the shoes to rest in wait for the next time around when the brake pedal is released. Also incorporated in both the rear wheels is the parking or emergency brake. The cable connected to the parking brake handle or lever is connected to the shoes through another set of levers. The parking brake operates independently of the main system for parking, or in case of emergency when and if the main system fails.

Which Part?
The first step was to jack up the front of the truck and check the wheels. No dragging or grabbing on the forward end meant the problem was definitely out in the drum brake-equipped back. There are a few different parts of the drum brake setup that could cause brakes to get stuck or drag. We narrowed it down to three possibilities.

1) Rusted or Stuck Parking Brake Cable:

Rust can cause the cable to get jammed in its housing. Even when the parking brake lever is released the cable stays put. Since the cable pulls one of the shoes against the drum the wheel drags. Stuck parking brake cables can be checked without disassembling the brakes.

2) Over-Adjusted Adjusters

The brake adjuster is supposed to automatically position the shoes near but not against the drum as the friction material of the shoes wears out. Sometimes the adjuster goes haywire and pushes the shoes out too far, causing them to drag against the drum.

3) Corroded and Stuck Wheel Cylinders

A stuck wheel cylinder can also cause the same problem as a stuck adjuster. Neglecting brake fluid can cause corrosion to form inside the system. The wheel cylinder gets stuck in the open position and the brake shoes push out against the drum even after the brakes are released.

In this case the brake adjusters had over-adjusted and caused the shoes to bind onto the drum. Follow along to see how we got there.

How To Photo Guide:

We started with jacking up the vehicle and lowering it onto jack stands. Before attempting to go any further, make sure to get a service or repair manual. Tip: loosen wheel lug nuts slightly before jacking up the rear or front end.1) We started with jacking up the vehicle and lowering it onto jack stands. Before attempting to go any further, make sure to get a service or repair manual. Tip: loosen wheel lug nuts slightly before jacking up the rear or front end.

Inspection of the parking brake cables showed no signs of severe rust or binding. Yank on one end of the cable and watch to see if the lever on the drum backing plate moves freely. Now is a good time to squirt some cable lube into the housings.2) Inspection of the parking brake cables showed no signs of severe rust or binding. Yank on one end of the cable and watch to see if the lever on the drum backing plate moves freely. Now is a good time to squirt some cable lube into the housings.

On to the brakes: Brake drums can be stubborn to remove. A quick once-around with a plastic faced hammer can help loosen the drum's grip on the shoes. If the drum remains stubborn try backing off the adjuster.3) On to the brakes: Brake drums can be stubborn to remove. A quick once-around with a plastic faced hammer can help loosen the drum's grip on the shoes. If the drum remains stubborn try backing off the adjuster.

With the drum off the axle, we saw that everything looked good. There was still plenty of meat on the shoes and there were no signs of any leaking gear oil or brake fluid. Tip: Always leave one side of the brakes assembled for reference.4) With the drum off the axle, we saw that everything looked good. There was still plenty of meat on the shoes and there were no signs of any leaking gear oil or brake fluid. Tip: Always leave one side of the brakes assembled for reference.

Since the truck had been sitting for a long time, we removed and inspected the wheel cylinders. Look for pitting and corrosion inside the bore. These looked fine. We reassembled them with fresh brake fluid and back they went.5) Since the truck had been sitting for a long time, we removed and inspected the wheel cylinders. Look for pitting and corrosion inside the bore. These looked fine. We reassembled them with fresh brake fluid and back they went.

Here is what the adjuster looks like. In this case the adjuster had turned out too far and was causing the shoes to bind against the drum. We took the adjuster apart, added some fresh grease, and returned it in its shortest position.6) Here is what the adjuster looks like. In this case the adjuster had turned out too far and was causing the shoes to bind against the drum. We took the adjuster apart, added some fresh grease, and returned it in its shortest position.

It may be necessary to bring the adjuster back where it's supposed to be, otherwise the shoes will have to travel too far to contact the drum. This will cause low pedal, which can be dangerous. The screw is designed to turn one way. Turn it until a slightest amount of drag is heard.7) It may be necessary to bring the adjuster back where it's supposed to be, otherwise the shoes will have to travel too far to contact the drum. This will cause low pedal, which can be dangerous. The screw is designed to turn one way. Turn it until a slightest amount of drag is heard.

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