Chrysler 1998 Voyager Service Manual page 88

5 - 6 BRAKES
DESCRIPTION AND OPERATION (Continued)
Fig. 6 Fixed Proportioning Valve Location
FIXED PROPORTIONING VALVE OPERATION
The fixed proportioning valve is made out of alumi-
num and has an integral mounting bracket. The
fixed proportioning valve is non-serviceable compo-
nent and must be replaced as an assembly if found to
be functioning improperly.
The fixed proportioning valve is mounted to the
bottom of the left rear frame rail, just forward of the
rear shock absorber to frame rail mounting location
(Fig. 6). The proportioning valve has 2 inlet ports for
brake fluid coming from the ABS modulator, and 2
outlet ports for brake fluid going to the rear wheel
brakes.
The fixed proportioning valve operates by allowing
full hydraulic pressure to the rear brakes up to a set
point, called the valve's split point. Beyond this split
point the proportioning valve reduces the amount of
hydraulic pressure to the rear brakes according to a
certain ratio.
Thus, on light brake pedal applications the propor-
tioning valve allows approximately equal brake
hydraulic pressure to be supplied to both the front
and rear brakes. On heavier brake pedal applications
though, the proportioning valve will control hydraulic
pressure to the rear brakes, so that hydraulic pres-
sure at the rear brakes will be lower than that at the
front brakes. This controlled hydraulic pressure to
the rear brakes prevents excessive rear wheel ABS
cycling during moderate stops.
HEIGHT SENSING PROPORTIONING VALVE
CAUTION: The use of after-market load leveling or
load capacity increasing devices on this vehicle are
prohibited. Using air shock absorbers or helper
springs on this vehicle will cause the height sens-
ing proportioning valve to inappropriately reduce
the hydraulic pressure to the rear brakes. This inap-
propriate reduction in hydraulic pressure potentially
could result in increased stopping distance of the
vehicle.
On vehicles not equipped with ABS brakes, the
brake systems hydraulic control unit (HCU) is
replaced by a junction block (Fig. 7). The junction
block is made of aluminum and is mounted to the
front suspension crossmember on the drivers side of
the vehicle in the same location as the (HCU) on an
ABS equipped vehicle. The junction block is perma-
nently attached to its mounting bracket and must be
replaced as an assembly with its mounting bracket.
The junction block is used for diagonally splitting the
brake's hydraulic system.
Fig. 7 Junction Block Location
Vehicles not equipped with ABS brakes use a
height sensing proportioning valve. The height sens-
ing proportioning valve is mounted on the left frame
rail at the rear of the vehicle (Fig. 8). The height
sensing proportioning valve uses an actuator assem-
bly (Fig. 8) to attach the proportioning valve to the
left rear spring for sensing changes in vehicle height.
Fig. 8 Height Sensing Proportioning Valve
HEIGHT SENSING PROPORTIONING VALVE OPERATION
The height sensing proportioning valve regulates
the hydraulic pressure to the rear brakes. The pro-
portioning valve regulates the pressure by sensing
the load condition of the vehicle through the move-
ment of the proportioning valve actuator assembly
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