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Do-It-Yourself Projects
Diagnosing Rear Drum Brake Drawbacks
By Mike Bumbeck/autoMedia.com
Printable version
Degree of DifficultyModerate
Moderate
Estimated Time240 minutes
240 minutes
How to Repair Pesky Brake Problems -
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.
Diagnosing Rear Drum Brake Drawbacks
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.
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