How to Diagnose a Pulsating Brake Pedal
A pulsating brake pedal may indicate brake parts worn beyond their limits or loose components. Excessive lateral run-out or thickness variation also may cause this condition. Diagnose a pulsating brake pedal by implementing the following steps.
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Instructions
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Determine if the pedal feels firm or mushy. A soft, mushy or spongy feeling could result from leaks in the brake lines. Examine the pedal to see if it slowly sinks which may indicate a worn-out master cylinder. Look for worn or loose brake parts.
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2
Look for excessive lateral run-out. This refers to a rotor's wobbly movement. Rotor run-out should not exceed .002 and .005 inches. Brakes may produce pulsation, noise or vibration when the run-out exceeds this range. Excessive run-out can push the pads too far from the rotor.
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Inspect loose components, such as wheel bearings or calipers that can cause rotor thickness changes. Lack of parallelism or variation in rotor thickness can produce the same factors that cause run-out. Look for loose wheel bearings, lateral rotor run-out, uneven torque or a dragging caliper that causes the friction material to contact the rotor.
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Pinpoint parallelism with a micrometer that measures rotor thickness for at least four equally spaced points about an inch from the edge.
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Examine lug nut torque. A lug nut with five pounds more pressure on it can cause a rotor to warp. When tightening the lug nuts, follow a two-step process in a star pattern and use a torque wrench, a tightening device that yields equal pressure. Tighten the lug nuts to half the necessary torque, and then use the wrench to secure the nuts to the final torque specification.
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Comments
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I took my car for new breaks. When I drove it hime I noticed the peted pulasting,,, took it bace,,, macanic said breaks are fine. Been driving it that wat wor two monts, Last week my som drove the car and said, Mom you car really needs to go back...there is something wrong with your breaks. To my sorrow...I don't have the reciepe...any help?
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polychromeugand
Oct 07, 2010
In section 5 the statement "A lug nut with five pounds more pressure on it can cause a rotor to warp" is nothing more than useless fear mongering. An engineer can tell you (and this one will) that the torque is beside the point; its the clamping force created by the elastic elongation of the steel stud. The problem is that the correlation between the applied torque and the clamping force is quite variable. The torque has two parts, the translated clamping force and friction. In the end, the friction is larger. If it wasn't the lug nut would spin back off the stud and we'd all be putting lock washers and loctite on the wheel studs. The actual friction depends on a lot of factors that come down to materials, and surface condition, the properities of any lubricants - like anti-seize - that are present. The simple fact is that if you instrument a wheel stud with a strain gauge and...
