GMC 1986 P-Truck Service Manual page 435

PROPORTIONING VALVE ADJUSTMENT
If a front wheel lockup is experienced when the
vehicle is being operated near the maximum GVWR
with a lower than desired brake application, the valve
adjustment should be checked. Use the following
procedure to check the adjustment.
1. Raise the vehicle.
• Support the frame with suitable safety
stands. The axle must be allowed to hang
free.
2. Remove the nut from the valve shaft.
• Remove the lever.
3. Select the appropriate adjustment gage from the
chart.
46. Bolts
47. Washer
48. Nut
49. Lever
50. Valve
51. Brake Pipe
Figure 10—Removing Proportioning Valve
Figure 9—Height Sensing Proportioning Valve
51 50
48
B-07783
ADJUSTMENT GAGE CHART
Part
Number Code Color
14061394 A Green
14061395 B Black
14061396 C Blue
RPO G52: Extra Capacity Rear Spring
RPO LS9: 5.7 Liter (Cal. Only)
RPO LL4: 6.2 Liter
RPO LT9: 5.7 Liter
4. Rotate the valve shaft to permit the installation of
the adjustment gage (figure 11).
• The center hole of the adjustment gage
must seat on the " D" shape of the valve
shaft.
• The gage tang must seat in the valve
mounting hole.
NOTICE: Do not drive lever assembly on valve
shaft by using nut or proper valve setting may
be disturbed.
5. Install the nut on the shaft. Torque to 10 N-m (89
in. lbs.)
6. Sever the tang on the adjustment gage (figure
12
).
7. Remove the safety stands.
• Lower the vehicle.
• Test the brakes.
BRAKES 5-15
Vehicle Combination
C/K 3500 with G52
C3500 Less G52
C2500 all
K 20903
G31305/06 with LE3/LS9
K3500 Less G52
K20906
G31305/06 with LLA/LT9