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Hummer I(Edit)

Full-time all wheel drive.

Transfer case: All HUMMERs use a New Process Gear (NPG) 242 2sp transfer case. It is a full time transfer case incorporating an open differential between the front and rear driveshafts (DS). It has 4 modes, High (H), High Locked (HL), Low (locked) (L), and Neutral (N). The ratios are 1:1 in high, 2.72:1 low.

Military versions have a 50/50 split, civil versions a 48/52 split via the planetary gear differential. Military TC has a mechanical speedometer output and a larger oil cooling loop.

The input shaft and rear output shaft are co-linear. The front is a left handed output, chain driven.In H, the normal operating position, torque is evenly split front and rear via the transfer case's differential. This center differential is open and allows the front and rear driveshafts to turn at different rates to allow turning on high traction surfaces. In HL, the differential is locked (manual locker), forcing the front are rear driveshafts to turn at the same rate. This is equivalent to a part-time 4wd system. The L position forces the input shaft to turn a planetary gear assembly at the front of the case. The ring gear is machined into the front case. Low adds a gear reduction of 2.72:1. The differential is always locked in low. The N position disconnects the input from the output shafts totally. The differential is open in this position. A sensor at the rear of the transfer case (TC) is used to determine speed. Another sensor determines if the TC differential is locked or unlocked, illuminating a status light. The TC is cooled via transmission fluid flowing through an intercooler inside the TC. The engine, transmission, and transfer case are rigidly connected together. The assembly is canted slightly to the right.

Differentials: The differential case is a Dana (AMC) 20, hypoid (top entry), same as in some older Jeeps (AFAIR). The differential has a ratio of 2.73:1. HUMMERs use Zexel-Gleason Torsen torque sensing/biasing (front and rear) differentials. These are not a limited slip design or locking design. The bias ratio is 3.8:1 AFAIK. Since the suspension is independent, the differential case is connected to the frame.

Optional Eaton ELocker locking differentials front and rear.

Source: Gerald's HUMMER Page

Do you own Hummer I? Can you please make a photo of the car's 4x4 transmission, switches, dashboard lights, etc. and send it to ?

Hummer II(Edit)

Borq-Warner 4484 transfer case.

Full-time all wheel drive with 40/60 torque distribution via planetary gear differential, which can be locked manually (Source).

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Hummer III(Edit)

Either the B-W 4493 or 4494 (greater low-range reduction).

Full-time all wheel drive with 40/60 torque distribution via planetary gear differential, which can be locked manually (Source).

Do you think this information about Hummer Iii is incorrect? Please send us what you know to or leave a comment below.

There is 1 comment
October 31, 2009 - 20:12

The torque split of the H1 is 48/52, not an even 50/50.

The Hummer II utilized the Borq-Warner 4484 transfer case.

The Hummer III utilized either the B-W 4493 or 4494 (greater low-range reduction)

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