Dodge Omni/Horizon/Rampage 1978-1989 Repair Guide

Height Sensing Proportioning Valve

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OPERATION



The Rampage and Scamp pickup models use a height sensing dual proportioning valve in addition to the regular differential warning switch. This valve is located under the bed just forward of the rear axle. It automatically provides optimum brake balance front-to-rear regardless of the vehicle load condition. The valve modulates the pressure to the rear brakes sensing the vehicle load condition through relative movement between the rear axle and the load floor.



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Fig. Fig. 1 Location of the Rampage and Scamp pickup model height sensing dual proportioning valve


WARNING
It is important that aftermarket load leveling devices are NOT installed on this brake/suspension system. The installation of these devices will cause the rear brake height sensing proportioning valve to sense a light load condition that is actually a loaded condition being created by these add-on devices.

TESTING



When a premature rear wheel slide is obtained on brake application, it could be an indication that the fluid pressure to the rear brakes is above the reduction ratio for the rear line pressure and that the proportioning valve is malfunctioning. To test the valve use the following procedures.


WARNING
During the testing, leave the front brake lines connected to the valve.

  1. Disconnect the external spring at the valve end.
  2.  
  3. Install one gauge and the tee of tool set C-4007-A, or equivalent in the line from either master cylinder port and brake valve assembly.
  4.  
  5. Install the second gauge from tool set C-4007-A or equivalent to either rear brake line. Bleed the rear brake system.
  6.  
  7. Have an assistant exert pressure on the brake pedal (holding pressure) to get a reading on the valve inlet gauge and check the reading on the outlet gauge. The inlet pressure should read 1000 psi (6895 kPa) and the outlet pressure should read between 530-770 psi. (3654-5309 kPa). If either is not as specified, replace the valve.
  8.  

INSTALLATION & ADJUSTMENT




WARNING
After installing a new height sensing proportioning valve, both rear brakes should be bled.

  1. Raise the vehicle and support on jackstands so that the rear suspension is hanging free and the shock absorbers are fully extended. Leave the wheels and tires on the truck to help keep the suspension in the full rebound position.
  2.  



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Fig. Fig. 2 Adjustment on the height sensing proportioning valve

  1. Loosen the spring adjusting bracket nuts A and B .
  2.  
  3. Push the valve lever C rearward until it bottoms and hold it there.
  4.  
  5. Rotate the spring adjusting bracket D rearward until all the free play has been removed from the spring. (Be careful not to stretch the spring). While holding the adjusting bracket in position, release the valve lever. Tighten nut B temporarily, to hold the adjusting bracket in this position.
  6.  
  7. Mark the position of the adjusting bracket nut B on the bracket support E .
  8.  
  9. Loosen nut B and rotate the top of the adjusting bracket rearward so that nut B is 1 / 8 in. (3mm) forward of the no free play position. Tighten nut B to 21 ft. lbs. (28 Nm) while being careful not to move the bracket. Tighten nut A to 21 ft. lbs. (28 Nm).
  10.  

 
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