Brakes Work Example 10

WorkKey Level: 4
NATEF Automotive Tasks: V.A

A proportioning valve is suspected of being bad. You hook up a pressure gauge at the master cylinder and one at the wheel cylinder. The spec says there should be at least a 10% reduction in pressure at the rear. Pressure is applied and the following pressures are recorded.

                        Front    900 pounds

                        Rear     820 pounds

Is the valve doing its job?  Please explain.

Solution:

A 10% reduction in the rear would be calculated as follows:
(900)(10%) = (900)(0.10) = 90 pounds
900 – 90 = 810 pounds

No, the valve is not doing its job.  Rear pressure needs to be at most 810 pounds.