Shock Absorbers; Inspection - PREVOST H3-41 Maintenance Manual

SECTION 16 : SUSPENSION
supports. Thread the lower nuts and the
small upper nut a few turns.
NOTE
To facilitate air spring installation, compress it
manually then put a piece of tape over the air
line threaded fitting. This prevents air from
getting back into the bag and keeps it
compressed, thus enabling to place the bag in
between the mounting plates and greatly
easing installation.
2. Tighten and torque the lower stud nuts, and
then the upper one as prescribed in Torque
Table 3.
3. Thread the remaining upper nut (large nut)
and tighten as prescribed in Torque Table 3.
4. Install elbow (if applicable), then connect air
line.
5. Connect the height control valve link.
6. Build up air pressure in system.
NOTE
To accelerate this operation, air reservoirs can
be filled from an exterior air supply connected
to the accessory tank fill valve or to the
emergency fill valve.
7. Check operation of bellows, and with the
primary air system at normal operating
pressure (122 - 140 psi (841 - 965
kPa)),coat the air line connections and air
spring mounting areas with a water and soap
solution. Bubbles will indicate an air leak,
and none is permissible. Repair or replace
defective parts.
8. Reinstall wheel.
9. Remove the hydraulic floor jack from under
the axle, then lower vehicle to ground.
5.2

SHOCK ABSORBERS

Double-action, telescoping-type shock absorbers
ensure a smooth ride and enhance vehicle
stability on the road. The tag axle is provided
with two shock absorbers while the drive axle is
provided with four of them (Figure 39).
44 PA1621 Maintenance Manual All Series | Section revised October 2018
Shock absorbers are non-adjustable and non-
repairable. Maintenance requirements involve
replacement of the rubber mounting bushings,
and tightening of all shock absorber mounting
pins at the proper torque (refer to Torque Table
3) when shock absorber replacement occurs. If a
shock absorber becomes inoperative, complete
unit must be replaced.
CAUTION
When a shock absorber is found defective,
always replace with a new set on affected
axle, except if there has been a recent
replacement of one unit. The following method
will help in determining if both shock absorbers
on the same axle have to be replaced.
5.2.1

Inspection

Loosen lower mounting of both shocks, and then
carefully attempt to raise and lower the bottom
portion of each shock. Note the rate of effort for
distance of travel. Replace both shocks if a
definite differential rate is found.
The shock must be bench checked in an upright,
vertical position. If checked in any other position,
air will enter the cylinder tube and make the
shock absorber appear defective.
Proceed as follows to check shock absorbers:
1. With the shock absorber in a vertical position
(top end up), clamp the bottom mount in a
vise.
CAUTION
Do not clamp the reservoir tube or the dust
tube.
2. Rotate the dust tube. Notice any binding
condition (may be compared with new unit).
Binding condition indicates a scored rod.
Units with scored rods should be replaced.
3. Fully extend shocks and check for leaks in
the seal cover area. Shock fluid is a very thin
hydraulic fluid that has a characteristic odor
and dark brown tint. A slight trace of shock
fluid around the seal cover area is not a
cause for replacement. The shock seal is
designed to permit a very slight seepage to
lubricate the rod. Units that leak should be
replaced.