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Driving with parking brake on

Driving with parking brake on — what to do next?

Of course it was an accident. But driving with parking brake on happens all the time. If you only drove for a short distance, you’re probably ok. However, if you drove a long distance and noticed a burning smell, you may have caused damage. Here’s what happens when you drive with the parking brake on.

The parking brake only works the back wheels

When you apply the parking brake, it only applies braking force to the rear wheels.

Driving with parking brake on with rear drum brakes

In a drum brake setup, the normal brake shoes are mechanically forced against the drums by the parking brake cable. If you drive for long periods with the brake shoes in contact with the drums, you’ll overheat the brake shoes and drums and possibly overheat the brake fluid.

Let the system cool down completely before checking.

overheated brake shoes

Overheated brake shoes — glazed and cracked

Then, remove the brake drum and look for signs of overheated metal (blue or rainbow colors on the friction area of the drum). If you find those, you must replace the drum. Next, check for glazing on the brake shoes. If the brake shoe friction material is shiny, they should be replaced. In the old days, techs would sand them, but that’s no longer recommended.

Finally, check the condition of the springs and wheel cylinders. Overheating can cause the springs to break or lose tension and it can also damage the rubber seals in the wheel cylinder. If you see any brake fluid leaks, replace the wheel cylinder and install new springs.

Driving with parking brake on with rear disc brakes

There are two types of parking brakes for vehicles with rear disc brakes: parking mechanism internal to the caliper and drum-in-hat.

In an integral design, the parking brake cable pushes the caliper piston out mechanically, as opposed to hydraulically. In this design, if you drive with the parking brake on, you can damage both the rear brake pads and the rotor and in extreme cases, also the caliper.

In a drum-in-hat design, the rear disc brake operates normally, while the parking brake uses a shoe or ring setup to apply friction to the drum-in-hat rotor. If you drive with the parking brake on in this design, you can damage the parking brake shoes, but usually not anything else.

drum in hat parking brake

Posted on by Rick Muscoplat

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