Question: What is a common cause for pedal pulsation that presents itself shortly after a brake job has been performed?
Answer: Today’s vehicles are staying on the road much longer. The square cut seal in the caliper can become stiff and prevent the piston’s return. While no leaks are visible, this condition keeps the piston from retracting and causes the friction material to drag. The buildup of friction material on the rotor face then creates pulsations that would not have otherwise occurred.
Question: Is there a way to quickly check for air in a base brake hydraulic system?
Answer: A little trick is to remember that air is highly compressible. Have someone firmly hold down the brake pedal while the engine is running. Watch the master cylinder reservoir and have your partner release the pedal. If there is air in the system, a large spout of fluid will come out of the vent port. If no air is present, very little fluid will release because the air-free circuit will simply release the amount of fluid required to apply the brakes.
Question: What is a common cause of premature ABS brake application?
Answer: Premature ABS applications are mostly caused by speed sensor issues. Rust build up under the speed sensors is one common cause as seen on General Motors light-duty trucks. The speed sensor output voltage drops as it moves away from the tone wheel and is interpreted as a slipping wheel. Then as it moves a little further, an ABS variable voltage speed sensor code can be set.
Question: Should there be any dampening products applied to the back of disc brake pads?
Answer: A number of "dampening" chemicals were used for older vehicles that had the consistency of adhesives and were designed for pads that did not use shims. That means there are virtually no applications on today’s vehicles that need these chemicals. If used on pads with shims, they may actually cause the shim to come off the pad, creating shim migration issues. A light coat of high quality non-petroleum based brake lube can be put on the piston faces and caliper-to-pad contact areas to reduce noise without restricting movement.
Question: Is it necessary to machine new rotors?
Answer: Premium quality rotors are machined on very accurate CNC lathes. These lathes cost upwards of $1 million and feature 18" vertical arbors and use ceramic cutters that work at high speeds and machine many rotors in one operation. Basically, if the surface smoothness is below 70 to 80 Ra, then it is smooth enough to use. If you choose to machine new rotors regardless, any removal of metal increases the temperature the rotor will operate at, reduce cooling, and can increase occurances of rotor runout.
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