Proportioning Valve
NOTE:
For proportioning valve testing on Anti-Lock Brake System (ABS), see the BRAKE SYSTEM - ANTI-LOCK article.
NOTE:
A premature rear wheel skid during hard braking may be caused by a defective proportioning valve located on left frame rail, below master cylinder. Proportioning valve is divided into 2 separate systems, one system for right rear brake and one system for left rear brake.
- Proportioning valve is located on left frame rail, below master cylinder. See Fig 1 . Road test vehicle to determine which rear wheel indicates a premature wheel skid.
- If right rear wheel skids first under hard braking condition, install pressure gauge and "T" fitting of Tester Set (C-4007-A) in master cylinder secondary brakeline at proportioning valve. See Fig 2 . Install second pressure gauge in brakeline to right rear brake. See Fig 2 . Go to step 4).
- If left rear wheel skids first under hard braking condition, install pressure gauge and "T" fitting of Tester Set (C-4007-A) in master cylinder primary brakeline at proportioning valve. See Fig 2 . Install second pressure gauge in brakeline to left rear brake. See Fig 2 . Go to next step.
- Bleed air from pressure gauges. Have an assistant hold brake pedal down until inlet pressure at proportioning valve is 1000 psi (70 kg/cm2 ) and note outlet pressure on proportioning valve. On 1996 models, outlet pressure should be 600-700 psi (42-49 kg/cm2 ). On 1997 models, outlet pressure should be 725-850 psi (51-60 kg/cm2 ). Replace proportioning valve if outlet pressure is not within specification.
- Remove test equipment. Reinstall brakelines on proportioning valve. Tighten brakeline nuts to specification. See TORQUE SPECIFICATIONS . Bleed brake system. See BLEEDING BRAKE SYSTEM .