Hummer H1 Service Manual page 210

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TRANSMISSION SERVICEABILITY
The Hydra-matic transmission used in Hummer vehicles is ser-
viced at two levels. Only external parts are serviced during the
warranty period. A transmission internal component failure
will require transmission replacement. Service replacement
transmissions are available through the DCS.
External repairs include replacement of the following:
• oil pan, gasket, magnet and filter
• converter housing access covers
• shift solenoids
• pressure switch
• speed sensors
• pressure control solenoid
• converter clutch solenoid
• park lock detent, actuator, pawl, pin, spring shift, plug,
and bracket
• torque converter and seal
• fill tube, seal, and dipstick
• adapter and gasket
• rear mount insulator and bracket
• transmission wiring harness
• vent lines and cooler lines
• PCM
TRANSMISSION DIAGNOSIS
Transmission diagnosis is a three step procedure. The first step
involves two preliminary inspection procedures to check exter-
nal parts. The second step involves road testing to confirm and
identify a problem. The third step involves shop testing to lo-
cate the problem system or part. Shop testing includes pressure
testing, scan tool diagnosis, and visual inspection.
Preliminary Inspection - Vehicle is Driveable
1. If problem involves vibration or noise, check following:
• tires and wheels for wear or damage
• drive belt and accessories for wear, or being loose
• propeller shaft U-joints for wear or damage
• exhaust pipes, muffler, converter touching body or
frame
• engine/transmission mount wear or damage
2. Check transmission fluid condition as follows:
a. Refer to Transmission Fluid Checking Procedure
3. Check transmission fluid level as follows:
a. Transmission fluid should be at normal operating
temperature for accurate check. Drive vehicle if
necessary.
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Transmission/Transfer Case
b. Start engine, apply brakes, shift through all gear
ranges and back to Park. Run engine at curb idle
speed.
c. Remove dipstick and check fluid level. Fluid should
be in crosshatch area of dipstick.
d. If level is low, add fluid in 1/4 pint/liter increments if
necessary. If fluid level is high, draw-off excess with
suction gun and plastic tubing inserted in filler tube.
CAUTION: Do not overfill the transmission. Excess fluid will
be churned into foam aerating the fluid. The result will be fluid
overheat, shift problems and clutch wear.
4. If fluid level was low, check for leaks at the oil pump seal,
cooler and lines, filler tube and oil pan.
5. Check shift linkage adjustment. If vehicle starts only in
Park and Neutral, linkage is OK. Linkage needs
adjustment when engine won't start in one of the ranges,
or if shift indicator in bezel is seriously misaligned.
6. Inspect transmission harness and case connector. Repair
loose connections or damaged wiring as needed and
proceed to next step.
7. If leaks, linkage, or fluid problems are not encountered,
proceed to road test.
Preliminary Inspection - Vehicle Is Disabled
1. Check fluid level and condition as described in procedure
for driveable vehicles.
2. Check for fluid leaks or broken shift linkage.
3. Check driveline as follows: Raise vehicle so wheels are
free to rotate. Then start engine, shift transmission and
transfer case into gear, and note the following:
a. If one or both propeller shafts turn but wheels do not,
problem is with differential or axle shafts.
b. If propeller shafts turn but transmission or transfer
case is noisy, stop engine immediately. Then repair
transmission or transfer case as needed.
c. If propeller shafts do not rotate and transmission is
not noisy, test transmission line pressure as described
in this section.
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