Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/636156
26 | February 2016 The Chassis of uneven or over-tightening of the wheel fasteners, can easily create a pulsating brake pedal. Aside from the annoying feel of this, if the pedal is pulsating/bouncing, this means that the pads are not in a con- sistent full contact with the disc surface, which results in a varying contact patch between the disc and pad, which reduces braking effciency. Measuring lateral runout is a simple process, and there's no reason to avoid the task. With the wheel removed, install all of the wheel fasteners to secure the rotor to the hub. Installing only two or three fasteners can result in an erroneous runout reading. This is especially critical when dealing with thin-hat rotors. Uneven and incomplete defection at the hub can easily result in warped discs that display excessive runout. Always install and fully torque to specifcation all of the wheel's fasteners. In order to avoid damaging the nut seat surfaces, it's also a good idea to install coni- cal washers between the nuts and rotor hat surfaces. As an example, by installing only two nuts on a fve-bolt hub, you might obtain a runout reading of, say, 0.005-inch. By installing three nuts the reading might be 0.003-inch. But by installing all fve, the reading may be 0.002-inch, which would be within spec. Mount a dial indicator to a stationary area that doesn't move in relation to wheel rotation (frame, strut, etc.). Dial indicator mounts are available with magnetic bases or clamp-on designs. Position the dial indi- cator's plunger at 90 degrees to the disc surface, and push the plunger in to provide about 0.050-inch preload. Then zero the In order to conduct lateral runout and thickness measurements, a dial indicator and thickness gauge are mandatory. The dial indicator requires a mount that will attach rigidly to a non- moving surface, such as the fexible-locking mount shown here. While a common micrometer can be used to measure thickness, a specialty rotor thickness caliper such as the one shown here features one pointed anvil and an opposing fat anvil, for more accurate measurement.