Hummer H1 (2002+). Manual - part 88

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 Transmission/Transfer Case  5-151

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05745159

OPERATING RANGES

The three operating ranges are for specific use on or off road.
Usage recommendations are:

High Lock (HL)

High lock range is for use on low traction surfaces. It is an un-
differentiated range and should only be employed on unpaved,
or low traction surfaces; low traction defined as surfaces cov-
ered by snow, ice, sand, mud, or dirt. The differential is by-
passed (locked out) in this range.

High (H)

High range is the only range recommended for use on hard, or
paved road surfaces. This range can be used on, or off-road as
desired.

Low (L)

Low range is for low speed, off road operation. The extra pull-
ing power provided is useful when traversing steep grades, or
driving in deep mud or sand. The low range gear provides a
2.72:1 reduction ratio when locked in the low range annulus
gear.

Neutral 

Neutral range is used for towing purposes.

TRANSFER CASE SHIFTING

The transfer case shift lever is adjacent to the transmission shift
lever. A straight-line shift pattern is employed (Figure 5-69).

The transfer case can be shifted from High (H) to High Lock
(HL) and back, at any legal speed without putting the transmis-
sion in neutral.

The vehicle must be completely stopped and the transmission
shifted to neutral before a shift to low range (L). This is neces-
sary because the low range gear must be moved into engage-
ment with the fixed annulus. Once the low range and annulus
are engaged, the transfer case is locked into a 2.72:1 reduction
ratio. All output to the propeller shafts is undifferentiated and
equal. Maximum recommended vehicle speed in low range is
23-31 mph (37-50 kph), with the lower speed preferred.

Figure 5-69:   Transfer Case Shift Lever and Bezel

TRANSFER CASE DIAGNOSIS

The diagnosis guides outline probable causes of various trans-
fer case malfunctions. The problem causes are listed in order of
potential (most to least probable). The guides do not cover ev-
ery possible condition or possibility. They do however, provide
a means of reducing the number of components requiring fur-
ther diagnosis and inspection.

TRANSFER CASE

OPERATING

RANGES

5-152

Transmission/Transfer Case

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TRANSFER CASE DIAGNOSIS

PROBLEM

POTENTIAL CAUSE

CORRECTION

Transfer Case 
Hard to Shift 
or
Will Not Shift 
Into Desired 
Range

1.

Vehicle speed too great to permit shifting.

2.

Vehicle driven for extended period on paved 
road surface in high lock (HL) range. Inter-
nal torque load can prevent shifting.

3.

Shift rod adjustment is incorrect.

4.

Shift control housing fault.

5.

Incorrect or low lubricant.

6.

Transfer case internal fault.

• sector damaged or loose

• range or mode fork failure

• damaged gear

1.

Reduce speed to 15 mph if shifting from H to HL 
and back. Stop vehicle completely if shifting into 
low range.

2.

Stop vehicle completely. Shift into neutral. Then 
into high (H) range. Do not operate vehicle on 
hard road surface in high lock.

3.

Adjust rod. Refer to procedure in this section.

4.

Remove and inspect housing shift arms. Replace 
housing if shift arm is damaged or binding.

5.

Add fluid, or drain and refill transfer case.

6.

Remove and overhaul transfer case.

Transfer Case 
Noisy In All 
Ranges

1.

Low lubricant level.

2.

Incorrect lubricant

3.

Shift rod mispositioned.

4.

Internal component wear or damage.

5.

Extended operation on paved roads in high 
lock range. (Causes accelerated bearing, 
wear, gear wear, and chain stretch.)

1.

Add lubricant and check for leaks. Correct leaks 
as needed.

2.

Drain and refill transfer case.

3.

Adjust shift rod as described in the section.

4.

Remove and overhaul transfer case.

5.

Inform driver that only high range should be used 
on paved surfaces. Repair transfer case if wear or 
damage has occurred.

Transfer Case 
Jumps Out Of 
Gear

1.

Not fully engaged in desired gear range.

2.

Shift linkage bind or misadjusted.

3.

Range or mode fork problem:
• fork cracked

• inserts worn, missing

• shift rail scored

• shift sector or shaft worn

4.

If transfer case jumps out of low range, prob-
lem is with low range gear, lockplate, or 
annulus.

1.

Stop vehicle, shift into gear, and resume opera-
tion.

2.

Adjust shift rod. Correct bind in control housing 
shift arm.

3.

Remove, disassemble transfer case and repair as 
necessary.

4.

Disassemble transfer case and repair as needed.

Lubricant Leaks 
From Vent Or 
Output Shaft 
Seals

1.

Transfer case overfilled.

2.

Vent or line restricted, kinked, pinched.

3.

Output seal failure (front or rear) caused by 
wear, incorrect installation, cut seal lip.

1.

Drain to correct level. Check transfer case cooler 
if transfer case is overfilled and transmission fluid 
level is low.

2.

Replace vent or line as needed. Reroute line to 
eliminate kinks.

3.

Replace seal(s). Correct cause of cut seal lip or 
abnormal wear of seal lip (rough surface on output 
shaft or yoke).

Rapid Tire Wear

1.

Vehicle driven for extended periods in high 
lock on hard, paved road surfaces.

1.

Inform driver that only high range should be used 
on hard, paved road surfaces.

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 Transmission/Transfer Case  5-153

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05745159

TRANSFER CASE SHIFT ROD SERVICE

Removal

1.

Unfasten snaps and pull velcro strips apart to open shifter 
boot cover. 

2.

Remove cotter pins and washers securing shift rod to shift
arm and range lever (Figure 5-70).

3.

Remove shift rod and trunnion as assembly. 

4.

Remove trunnion from shift rod if necessary.

Installation

1.

Install trunnion on shift rod.

2.

Connect shift rod and trunnion to shift arm and range
lever.

3.

Secure shift rod with washers and or cotter pins.

4.

Adjust shift rod. Refer to Shift Rod Adjustment procedure.

5.

Push velcro strips together and fasten snaps to close shifter
boot cover. 

Figure 5-70:   Transfer Case Shift Rod Attachment

Adjustment

1.

Apply parking brakes and shift transmission into neutral.

2.

Shift transfer case into high lock (HL) position.

3.

Disconnect shift rod and trunnion at control housing shift
arm (Figure 5-70).

4.

Verify that transfer case range lever is in high lock
position. This is last detent toward rear (Figure 5-71).
Move lever fully into detent if necessary.

5.

Adjust shift rod trunnion so it is slip fit in control housing
shift arm. Install washer and cotter pin in trunnion.

6.

Check shift rod adjustment. Be sure transfer case is firmly
engaged in each detent (range) position. Also be sure shift
lever aligns with range positions on shift lever bezel.

Figure 5-71:   Range lever Positions

VENT LINE REPLACEMENT

1.

Loosen clamp and remove vent line from fitting on rear of 
transfer case (Figure 5-72).

2.

Remove bolt, clamp, and vent line.

3.

If installing a new vent line, transfer clamp to new vent
line.

4.

Connect vent line to tee fitting.

5.

Connect vent line transfer case fitting and tighten clamp.

6.

Attach clamp and vent line to transmission. Tighten clamp
bolt to 16-20 lb-ft (22-27 N•m).

Figure 5-72:   Transfer Case Vent Line Routing

ADJUSTING

TRUNNION

TRANSFER CASE

RANGE LEVER

TRANSFER CASE

SHIFT ROD

CONTROL

HOUSING

SHIFT

SHIFTER BOOT

COVER (SHOWN OPEN)

WAVY

WASHER

FLAT

WASHER

WAVY

WASHER

FLAT

WASHER

COTTER

PIN

VENT LINE

FITTING

TEE FITTING

TRANSMISSION

TRANSFER CASE

5-154

Transmission/Transfer Case

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SPEED SENSOR AND/OR SWITCH 
REPLACEMENT

1.

Disconnect harness connector from vehicle speed sensor, 
lock indicator switch, and/or range indicator switch  
(Figures 5-73 and 5-74).

2.

Remove switch and/or sensor from transfer case
(Figures 5-73 and 5-74).

Figure 5-73:   Speed Sensor and Lock Indicator 

Switch Location

Figure 5-74:   Range Indicator Switch Location

3.

Install new switch and/or sensor in transfer case.

4.

Attach harness connector to switch or sensor.

GUIDE CABLE REPLACEMENT

1.

Remove bolts, nuts, and washers attaching cable bracket to 
muffler bracket (Figure 5-75).

2.

Remove bolts, nuts, and washers securing guide cable.

3.

Remove guide cable and bracket.

4.

Attach guide cable bracket to muffler bracket.

5.

Attach guide cable bracket to transfer case with washers
and nuts.

6.

Install guide cable and brake line support bracket. Tighten
bracket bolt to 27-33 lb-ft (37-45 N•m).

Figure 5-75:   Guide Cable Attachment

LOCK INDICATOR

SWITCH

VEHICLE

SPEED

SENSOR

WIRING HARNESS

RANGE

INDICATOR

SWITCH

MUFFLER

BRACKET

SUPPORT

BRACKET

GUIDE CABLE

BRACKET

TRANSFER

CASE

FRONT

PROPELLER

SHAFT

GUIDE CABLE