Car Doctor Q&A: A Braking Mystery in a Chevrolet Suburban

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Braking issues can make or brake (HA see what we did there) a fishing trip. Car Doctor John Paul investigates.

Q. I have a Chevrolet Suburban that I use on weekends for camping and fishing. After about a 30 minute ride the front brakes were locking up and acting just like I had my foot on the brake.

I jacked up the car and opened the brake caliper bleeder screws and the brakes acted normally again. The next time I drove it the same thing happened. This time I thought that the brake lines may be a problem so I replaced the two front brake lines that attach to the calipers. The next time I drove the truck about 3o minutes the same problem would happen. The only other part of the brake system that we have had replaced recently was the brake master cylinder. Could the problem be a defective master-cylinder?

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A. It is possible that the brake pedal is hanging up causing the brakes to apply. When the brakes start to drag are the brake lights on? If not it is possible the tolerance between the brake master cylinder and the brake power booster rod are too tight. As a test loosen up the bolts that secure the master cylinder to the power booster so there is about an 1/8th inch space. In now the wheels spin freely you have found your problem.

This video represents a different brake booster problem, but it covers how to loosen the nuts and remove one:

Some brake boosters have an adjustable push-rod, others you may need to shim slightly to achieve the necessary tolerance. Since the master-cylinder and brake booster are not a matched set, sometimes you need to adjust for proper tolerances.

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.

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John Paul