Modern Tire Dealer

APR 2019

Magazine for the professional tire industry

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Page 33 of 85

B r a k e s M T D A p r i l 2 0 1 9 32 retaining contaminants in the hydraulic system. Always remember to bench-bleed any master cylinder that has been emptied of fluid. An improperly bled master cylinder will result in a low, so pedal. is applies to a new unit as well as a used master cylinder that has been drained. is involves connecting temporary transfer tubes from the output ports into the reservoir(s), filling the reservoir(s) and slowly pushing the piston fully forward and slowly releasing several times until all traces of air bubbles are eliminated. In some cases, even aer bench bleeding via the output ports, it may be necessary to also bleed via the master cylinder's bleed ports (if so equipped). Once all trapped air has been released, be sure to keep the fluid level in the reservoirs sufficiently high to avoid exposing the outlet orifices at the bottom of the reservoir wells before installing the master cylinder. Naturally, during system bleeding, constantly keep an eye on the reservoir fluid level to avoid running the master dry. A note regarding the use of DOT 5 silicone brake fluid: Silicone fluid won't absorb moisture, and it won't damage a painted surface. Many customers choose this type of fluid because they assume that, since it won't absorb moisture from the air, this will prevent brake line/system corrosion. However, silicone fluid can still carry moisture on its surface, so while it may help to reduce the chance of corro- sion, it isn't a magic potion. e only real advantage of using silicone fluid is because it won't eat into a painted surface. During a fill/top-off, or if the system leaks, it may make a slimy mess, but it won't li paint from nearby areas. From a functional and performance aspect, it's simply not a good choice. Silicone fluid can become very unstable at tempera- ture, resulting in a low or ever-changing pedal feel. It's also affected by atmospheric Heavy rust or debris buildup inside a vented rotor can severely reduce heat dissipation and can lead to overheated and distorted/warped rotor discs. Even if the disc surface is or can be machined, if the vanes cannot be cleaned out, the rotor should be replaced. Regardless of the appearance of brake pad hardware, don't cut corners when servicing. Always replace all pad clips, pins and sliders.

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