Hummer H1 (2006+). Manual - part 200

5-40

Transmission/Transfer Case

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TRANSFER CASE OIL COOLER

The NP 242 used in HUMMER H1 vehicles is equipped with an internal cooler (Figure  5-19). The cooler is mounted within the
front case and secured by nuts and washers. O-rings are used to seal the cooler inlet/outlet tubes.  In operation, coolant from the ra-
diator flows through the transfer case cooler. Heat from the transfer case oil is transmitted to the coolant which is then conveyed to
the radiator.

Figure 5-19:   Oil Cooler Location

TRANSFER CASE IDENTIFICATION

An identification tag is attached to the rear case of each NP 242 transfer case  (Figure  5-20). The tag provides the model number,
assembly number, serial number, and low range ratio. The serial number also represents the date of build. For example, a serial
number of 10-10-99 would represent a build date of October 10, 1999.

Figure 5-20:   Transfer Case I.D. Tag Information

FRONT CASE

O-RING

TRANSFER CASE INTERNAL OIL COOLE

SUPPORT

BRACKET

10-1-08

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RECOMMENDED LUBRICANT

Dexron III is the recommended lubricant for the NP 242. Use it for topping off the fluid level and as replacement fluid for fluid
changes, or after overhaul. Dexron IIE can also be used for topping off a low fluid level when Dexron III is not readily available.

Do not use friction modifiers or similar additives in the NP 242. Use recommended lubricants only.

Transfer Case Fluid Level

Correct transfer case fluid level is to the lower edge of the fill plug hole. Recommended fluid is Dexron III.

The vehicle must be on a level surface for an accurate fluid level check. If the vehicle is raised on a hoist to check fluid level, a
drive-on style hoist is preferred. This type of hoist will keep the vehicle level.

The fill plug is just above the drain plug in the rear case. Tightening torque for the plug is 15-25 lb-ft (20-33 N•m).

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 undifferentiated range and should only be employed on unpaved, or low
traction surfaces; low traction defined as surfaces covered by snow, ice, sand, mud, or dirt. The differential is bypassed (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 de-
sired.

Low (L)

Low range is for low speed, off road operation. The extra pulling 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  5-21).

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

The vehicle must be completely stopped and the transmission shifted to neutral before a shift to low range (L). This is necessary
because the low range gear must be moved into engagement 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.

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5-42

Transmission/Transfer Case

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Figure 5-21:   Transfer Case Shift Lever and Bezel

TRANSFER CASE DIAGNOSIS

The diagnosis guides outline probable causes of various transfer case malfunctions. The problem causes are listed in order of po-
tential (most to least probable). The guides do not cover every possible condition or possibility. They do however, provide a means
of reducing the number of components requiring further diagnosis and inspection.

 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.

1.

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

2.

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

2.

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

3.

Shift rod adjustment is incorrect.

3.

Adjust rod. Refer to procedure in this section.

4.

Shift control housing fault.

4.

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

5.

Incorrect or low lubricant.

5.

Add fluid, or drain and refill transfer case.

1.

Transfer case internal fault.

• sector damaged or loose

• range or mode fork failure

• damaged gear

6.

Remove and overhaul transfer case.

TRANSFER CASE

OPERATING

RANGES

TRANSFER CASE
SHIFT LEVER

10-1-08

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 Transmission/Transfer Case  5-43

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VENT LINE REPLACEMENT

1.

Loosen the clamp and remove the vent line from the fitting on the rear of transfer case.

2.

Remove the bolt, clamp, and the vent line.

3.

Transfer the clamp to the new vent line.

4.

Connect the vent line to the tee fitting.

5.

Connect the vent line to the transfer case fitting and tighten the clamp.

6.

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

Transfer Case 
Noisy In All 
Ranges

1.

Low lubricant level.

1.

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

2.

Incorrect lubricant

2.

Drain and refill transfer case.

3.

Shift rod mispositioned.

3.

Adjust shift rod as described in the section.

4.

Internal component wear or damage.

4.

Remove and overhaul transfer case.

5.

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

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.

1.

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

2.

Shift linkage bind or misadjusted.

2.

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

3.

Range or mode fork problem:

• fork cracked

• inserts worn, missing

• shift rail scored

• shift sector or shaft worn

3.

Remove, disassemble transfer case and repair as
necessary.

4.

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

4.

Disassemble transfer case and repair as needed.

Lubricant Leaks 
From Vent Or 
Output Shaft 
Seals

1.

Transfer case overfilled.

1.

Drain to correct level. Check transfer case cooler 
if transfer case is overfilled and fluid appears 
milky for possible coolant leak.

2.

Vent or line restricted, kinked, pinched.

2.

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

3.

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

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.

 TRANSFER CASE DIAGNOSIS

PROBLEM

POTENTIAL CAUSE

CORRECTION

10-1-08