GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Proportioning Valve

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The proportioning valves, which are threaded into the master cylinder, limit outlet pressure to the rear brakes after a predetermined rear input pressure has been reached. This is used when less rear apply force is needed, and to obtain optimum braking and to prevent rear wheel lock-up on vehicles with light rear wheel loads.

REMOVAL AND INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Use a turkey baster or equivalent tool to siphon the brake fluid from the master cylinder into a suitable container.
  4.  
  5. Detach the electrical connector from the master cylinder.
  6.  
  7. Remove the master cylinder reservoir.
  8.  
  9. Remove the proportioning valve caps from the master cylinder.
  10.  
  11. Remove the O-rings, springs and the valve pistons. Be very careful not to scratch the valves in any way.
  12.  
  13. Remove the valve seals from the valve pistons.
  14.  

See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Exploded view of a non-ABS master cylinder



Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the proportioning valves, mounted in master cylinder

To install:
  1. Lubricate the new seals and the pistons with a suitable silicone grease. Place the seals on the valve pistons.
  2.  
  3. Install the valve pistons and O-rings into the master cylinder.
  4.  
  5. Install the valve cap assemblies and tighten to 20 ft. lbs. (27 Nm).
  6.  
  7. Install the reservoir assembly. Attach the electrical leads.
  8.  
  9. Connect the negative battery cable. Fill the master cylinder reservoir, then bleed the brake system as outlined later in this section.
  10.  

 
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