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Spongy Brakes Usually Boil Down to Fluid

March 01, 2000|RALPH VARTABEDIAN | TIMES STAFF WRITER

Question: During the heat of last summer, my brakes were spongy on many days. Now with the cooler weather, that's gone away. I had the brake fluid changed, but now my mechanic wants to change the vacuum booster, the caliper and the master cylinder. I need some advice on what caused the problem and whether I need all this stuff. --M.H.

Answer: Sounds like your mechanic wants to change out all the major components in your brake system, yet it's highly unlikely--though possible--that all of it is defective.

Spongy brakes are generally caused by gas inside the hydraulic system. Remember that all passenger vehicle brake systems use a hydraulic fluid that transfers force through high-pressure brake lines.

If you get any kind of air or other gas inside those lines, then it compresses when you hit the brakes without effectively transferring force. That results in a spongy feel at the brake pedal.

The most common cause of this is water contamination of the brake fluid. Brake systems generate a lot of heat at the discs or drums during use, and some of that heat gets transferred into the brake calipers or brake cylinders and up the hydraulic lines. The heat can cause water to vaporize into a gas, resulting in a spongy brake.

Another possible source of gas in the lines is the brake fluid itself. It can actually boil if the brake system gets too hot. One cause of excess heat is a sticky caliper or wheel cylinder that causes the brake pads to continually drag on the disc or drum. Defective springs on rear drum brakes can also cause dragging. A dragging front brake pad will usually cause a car to pull left or right.

The first step in addressing spongy brakes is to change the fluid, which you have already done. It is unlikely that a vacuum booster, which is the major component that provides power assist in power brakes, would cause the condition you describe.

If the brakes are operating properly now and you have had them inspected for safety, it is best to delay further repairs until the condition returns. If it does, then you should immediately have a mechanic diagnose the problem. A second opinion may help.

In general, it is wise to have your brake fluid changed periodically, even though few manufacturers recommend it. Besides causing spongy brakes, water in the brake fluid causes corrosion that can ruin calipers and brake cylinders. Brake fluid changes are relatively cheap, so you should have it done every year or two.

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Q: My 1998 Honda Accord EX went through the original rear disc brake pads at about 17,500 miles. I considered that to be premature and asked for a partial refund on the repair, but Honda just laughed at me. The company claimed this was normal brake wear and suggested that I left my parking brake on. I am 48, driving for 33 years, and consider myself a car buff. I think Honda makes lousy brakes but just won't admit it. What do you think? --M.W.

A: Not every Honda brake in history has been a model of design perfection, but the company has made many fine braking systems.

The longevity of brake pads depends on a lot of factors, including the kind of driving you do, the loads you carry and the terrain you cover. Still, 17,500 miles on rear brakes on a front-wheel-drive vehicle is below normal.

It's possible that the parking brake was adjusted improperly, the calipers are stuck or the discs are warped. Assuming that both the left and right pads wore out simultaneously at 17,500 miles, a stuck caliper or warped disc doesn't seem likely. A more complex problem, involving a one-way valve, may be affecting the hydraulic system or the anti-lock braking system.

Honda has not issued any technical service bulletins regarding such a problem, based on Mitchell Repair Information Co.'s database of technical service bulletins.

Since it appears your car is still under warranty, I would demand that the dealer perform a comprehensive exam of the brake system.

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Ralph Vartabedian cannot answer mail personally but responds in this column to automotive questions of general interest. Please do not telephone. Write to Your Wheels, Business Section, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053. E-mail: ralph.vartabedian@latimes.com.

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