Proportioning Valve
NOTE:
A premature rear wheel ABS cycling on a hard brake application may be caused by a defective proportioning valve. One proportioning valve is located on each rear wheel brake hydraulic circuit. Both proportioning valves must be checked to isolate defective proportioning valve.
- Road test vehicle to determine which rear wheel indicates a premature wheel skid. Remove suspect proportioning valve from brakeline.
- Using a brake pedal holding tool, depress brake past its first one inch of travel and hold in this position. This will isolate master cylinder from brake hydraulic system and will not allow brake fluid to drain out of master cylinder reservoir. Determine which proportioning valve needs to be tested. See Fig 1.
- Remove hydraulic brake tube from proportioning valve controlling rear wheel of vehicle that has premature wheel skid. Remove proportioning valve from outlet port on master cylinder.
- Install pressure test fitting Adapter (8644) into inlet port and Adapter (8187-2) into outlet port of proportioning valve. Install proportioning valve with adapters back into outlet port on master cylinder.
- Install Pressure Gauge (C-4007-A) into each adapter. Remove brake pedal holding tool. Bleed air from pressure gauges. Have an assistant hold brake pedal down until pressure on inlet side of proportioning valve is 1000 psi (70 kg/cm2 ) and note pressure on outlet side of proportioning valve. Pressure on outlet side should be 600-700 psi (42-49 kg/cm2 ). Replace the proportioning valve if pressure is not within specification.
- Remove test equipment. Install proportioning valve in master cylinder. Hand tighten until proportioning valve is fully installed and "O" ring seal is seated into master cylinder. Tighten proportioning valve to 30 ft. lbs. (40 Nm). Install brake tube on proportioning valve. Tighten tube nut to 145 INCH lbs. (17 N.m).
- Bleed brake system. See BLEEDING BRAKE SYSTEM . Once brake system is bleed, perform pressure test on remaining proportioning valve.