10. Install regulator spool assemblies into their re-
spective sleeve bores. The spherical end must be
inserted toward the spring seat. Push into bore
until contact is made with lower spring seat.
11. Install sleeve retainer plug packing (4) in valve
body.
12. Check to be certain spring seats (13 & 15) are
properly positioned into the regulator springs (14)
and the reaction plunger (8) slides smoothly in its
bore. Install retaining plug (5) in valve body coun-
terbore.
13. Position sleeve retainer (6) on valve body. Install
the four capscrews and washers (7), tightening
capscrews evenly to properly seat plug (5) in
counterbore. Final tighten capscrews to 140 - 150
in. lbs. (15.8 - 16.9 N.m) torque.
14. Tighten the two capscrews (20) holding the mani-
fold body (1) to the valve body (2) to 180 - 190 in.
lbs. (20.3 - 21.5 N.m) torque.
15. Install plugs (19) in manifold body ports. Tighten
the larger (#8 SAE) plugs to 275 - 300 in. lbs.
(31.1 - 33.9 N.m) torque. Tighten the smaller (#4
SAE) plugs installed in the “TC1” and “TC2” ports
to 90 - 100 in. lbs. (10.2 - 11.3 N.m) torque.
16. Install differential pressure switch on valve body
using new seals. Tighten capscrews to 140 - 150
in. lbs. (15.8 - 16.9 N.m) torque.
DIFFERENTIAL PRESSURE SWITCH
The differential pressure switch (3, Figure 3-11)
mounted on the dual relay valve detects an imbalance
in brake apply pressure between the left and right
wheels on the front or rear brake circuits.
If the regulated output pressures at the “B1” and “B2”
ports differ more than 300 psi (2068 kPa), the switch
(26) activates a warning horn and lamp in the cab to
alert the operator to a potential brake system problem.
Disassembly
1. Remove the four socket head capscrews attach-
ing the differential pressure switch body (3, Figure
3-11) to the dual relay valve body (2).
2. Remove switch assembly (26) and O-ring (25).
3. Remove plugs (28).
4. Remove screw plug (29).
5. Remove spring (30) and piston (31).
6. Carefully push spool assembly (32) out of its bore.
Cleaning and Inspection
1. Clean all metal parts with solvent and air dry.
2. Inspect spool assembly (32, Figure 3-11) and bore
for scoring and other evidence of damage. If spool
seals are damaged, the entire switch assembly
should be replaced.
3. Lightly lubricate spool assembly and insert in
bore. Spool must slide freely and smoothly in
bore. If there is binding, the entire differential
pressure switch assembly must be replaced.
4. Lubricate piston (31) and insert in its bore. Piston
must move freely with no binding.
5. Inspect spring (30) for cracks, distortion, etc.
6. Attach an ohmmeter to switch assembly (26)
center terminal and switch body. Actuate the
switch plunger to verify contacts close when
plunger is depressed and contacts open when
released.
Assembly
1. Install one plug (28, Figure 3-11) in the spool
assembly bore. Tighten plug to 190 - 210 in. lbs.
(21.5 - 23.7 N.m) torque.
2. Lightly lubricate Glyde rings on spool assembly
(32) and carefully insert in valve body bore until
seated against the plug.
3. Install plug in other end of spool bore. Tighten to
190 - 210 in. lbs. (21.5 - 23.7 N.m) torque.
4. Using new O-ring (25), install switch (26). Tighten
to 55 - 60 in. lbs. (6.2 - 6.8 N.m) torque.
5. Turn valve over and install piston (31), spring (30)
and screw plug (29). Plug should be inserted
approximately 0.5 in. (13 mm) below edge of
valve body. Temporarily install plug in screw plug
port.
NOTE: Screw plug (29) adjustment controls switch
actuation point. Refer to “Valve Test and Adjustment,
Differential Pressure Switch Adjustment ” for calibra-
tion procedure.
J3-18 Brake Circuit Component Service J03019 1/99
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