POWER TRAIN GRT880 SERVICE MANUAL
7-24
Published 10/19/2017, Control # 618-00
detent ball and spring in the direction spool provides three
positions, one each for forward, neutral, and reverse.
With the engine running and the directional control lever in
the neutral position, oil pressure from the regulating valve is
blocked at the control valve, and the transmission is in
neutral. Movement of the forward and reverse spool will
direct oil, under pressure, to either the forward or reverse
direction clutch, as desired. When either directional clutch is
selected, the opposite clutch is relieved of pressure and
vents back through the direction selector spool. The same
procedure is used in the speed selector.
The direction or speed clutch assembly consists of a drum
with internal splines and a bore to receive a hydraulically
actuated piston. The piston is oil tight by the use of sealing
rings. A steel disc with external splines is inserted into the
drum and rests against the piston. Next, a friction disc with
splines at the inner diameter is inserted. Discs are alternated
until the required total is achieved. A heavy back-up plate is
then inserted and secured with a snap ring. A hub with OD
splines is inserted into the splines of discs with teeth on the
inner diameter. The discs and hub are free to increase in
speed or rotate in the opposite direction as long as no
pressure is present in that specific clutch.
To engage the clutch, the control valve is placed in the
desired position. This allows oil under pressure to flow from
the control valve, through a tube, to a chosen clutch shaft.
This shaft has a drilled passageway for oil under pressure to
enter the shaft. Oil pressure sealing rings are located on the
clutch shaft. These rings direct oil under pressure to the
desired clutch. Pressure of the oil forces the piston and discs
against the heavy back-up plate. The discs, with teeth on the
outer diameter, clamping against discs with teeth on the
inner diameter, enables the hub and clutch shaft to be locked
together and allows them to drive as a unit.
There are bleed balls in the clutch piston which allow quick
escape for oil when the pressure to the piston is released.
Maintenance
General Information
1. Always check oil level with engine idling, and
transmission in neutral at normal operating temperature
(180 to 200°F (82 to 93°C)).
2. Change oil filter element every 500 hours. Drain and
refill system every 1000 hours or 6 months.
Troubleshooting
Following is an aid to locating the source of difficulty in a
malfunctioning unit. It is necessary to consider the torque
converter charging pump, transmission, oil cooler, and
connecting lines as a complete system when checking for
source of trouble, since proper operation of any unit depends
greatly on condition and operation of the others. By studying
principles of operation together with data in this section, it
may be possible to correct malfunctions which occur in the
system. Troubleshooting procedures basically consist of
hydraulic checks.
Hydraulic Checks
Before checking the transmission/torque converter and
associated hydraulic system for pressures and rate of oil
flow, it is essential that the following preliminary checks be
made.
1. Check oil level in transmission. This should be done with
oil temperature at 82°C to 93°C (180°F to 200°F). Do not
attempt these checks with cold oil.
2. To bring oil temperature to this level, it is necessary to
either work the machine or stall out the converter. When
it is impractical to work the machine, stall out the
converter as follows.
a. Apply parking brake and service brakes.
b. Position shift lever to forward and high speed.
c. Accelerate the engine to between half and three-
quarter throttle.
d. Hold converter stalled until desired temperature is
reached.
NOTE: Always make all troubleshooting checks with the
converter outlet temperature at least 82°C to 93°C
(180°F to 200°F).
CAUTION
Full throttle stall speeds for an excessive length of time
will overheat the torque converter.
Reference Only
To Next Page
Loading...
Need help?
General
