Posted by Ben on August 21, 19100 at 06:50:15:
In Reply to: Re: Fix for brake pulsating/vibrating posted by Dave on August 21, 19100 at 04:07:39:
Most disc brake calipers today "float" on the two pins that ride on these "O-Rings" and must slide easily within the holding tube, else they will bind.
As the disc pads wear, the caliper must slide over a bit to kept themselves "centered" in relationship to the rotor. The slide pins are solidly bolted to the suspension and do not move. The calipers have tubes that house the slide pins and is what the caliper uses to interface with the pins.
Our calipers are single pistion, which means there is only on piston that your foot pedal effort actuates. The piston then moves out against the disc pad backing plate, which contacts the rotor. The whole caliper assembly then moves in an opposite direction until the other side of the caliper contacts the other disc pad, which then contacts the other side of the rotor. Once this happens, the two pads squeeze the rotor and provide braking forces.
If one or both of the slide pins bind inside the caliper tubes, the whole assembly will not be allowed to "squeeze" the rotor, therefore no/less braking force is attained.
The reason there is a need for the "O-Rings" is that there is a tremendous amount of dirt, dust, etc that gets into everything in this area. It would compact and jam the sliding between the pin & tube. The O-Ring seals out the dirt, dust, etc. The part of the pin outside of the O-Ring does get theis junk on them, but is swept clean as the caliper moves over in time.
I personally like to fill the cavity between the two O-Rings with high temp grease each time I do a brake job. I've found plastic syringe like tools in the local hardware (Orchard) and fill them with the various greases I use.
The competition calipers have multi pistons and the calipers are usually "fixed" and do not slide or "float". The centering is by the two pistons and the hydraulic fluid between them inside the circuit.
-Ben