Jeep Cherokee (XJ): General information

NV3550 manual transmission

DESCRIPTION

The NV3550 is a medium-duty, 5-speed, constant mesh, fully synchronized manual transmission. Fifth gear is an overdrive range with a ratio of 0.78:1. The NV3550 is available in two and four-wheel drive configurations.

The transmission gear case consists of two aluminum housings. The clutch housing is a removable component. It is not an integral part of the transmission front housing.

A combination of roller and ball bearings are used to support the transmission shafts in the two housings.

The transmission gears all rotate on caged type needle bearings. A roller bearing is used between the input and output shaft.

The NV3550 has a single shaft shift mechanism with three shift forks all mounted on the shaft. The shaft is supported in the front and rear housings by bushings and one linear ball bearing. Internal shift components consist of the forks, shaft, shift lever socket, and detent components (Fig. 1).

GEAR RATIOS

Gear ratios for the NV3550 are as follows:

IDENTIFICATION

The NV3550 identification and part number bar code tags (Fig. 2) are located on the top of the transmission, forward of the shift tower.

OPERATION

The manual transmission receives power through the clutch assembly from the engine. The clutch disc is splined to the transmission input shaft and is turned at engine speed at all times that the clutch is engaged. The input shaft is connected to the transmission countershaft through the mesh of fourth speed gear on the input shaft and the fourth countershaft gear. At this point, all the transmission gears are spinning.

The driver selects a particular gear by moving the shift lever to the desired gear position. This movement moves the internal transmission shift components to begin the shift sequence. As the shift lever moves the selected shift rail, the shift fork attached to that rail begins to move. The fork is positioned in a groove in the outer circumference of the synchronizer sleeve. As the shift fork moves the synchronizer sleeve, the synchronizer begins to speed-up or slow down the selected gear (depending on whether we are up-shifting or down-shifting). The synchronizer does this by having the synchronizer hub splined to the mainshaft, or the countershaft in some cases, and moving the blocker ring into contact with the gear's friction cone. As the blocker ring and friction cone come together, the gear speed is brought up or down to the speed of the synchronizer. As the two speeds match, the splines on the inside of the synchronizer sleeve become aligned with the teeth on the blocker ring and the friction cone and eventually will slide over the teeth, locking the gear to the mainshaft, or countershaft, through the synchronizer.

Fig. 1 NV3550 Shift Mechanism

1 - 3-4 FORK
2 - SHIFT SHAFT LEVER AND BUSHING
3 - 1-2 FORK
4 - FIFTH-REVERSE FORK
5 - SHIFT SHAFT
6 - REAR HOUSING
7 - ROLL PIN
8 - SHIFT LEVER SOCKET
9 - SHAFT RAIL DETENTS
10 - FRONT HOUSING
11 - SHIFT SHAFT

Fig. 2 NV3550 Identification

1 - PART NUMBER TAG
2 - IDENTIFICATION TAG
3 - FRONT OF REAR HOUSING

Lubricant

DESCRIPTION

Required lubricant for the NV3550 is Mopart Manual Transmission Lubricant, P/N 4761526. This is the only lubricant to be used in NV3550 transmissions.

No other lubricants are acceptable, or recommended.

The correct transmission lubricant level is to the bottom edge of the fill plug hole (Fig. 3).

The transmission must be level to obtain an accurate lubricant level check. A drive-on type of hoist is recommended for this purpose.

Lubricant capacity of the NV3500 is approximately 2.28 liters (4.8 pints). This represents the approximate quantity needed to refill the transmission after a lubricant change or overhaul.

DRAIN AND FILL PLUG LOCATIONS

The NV3550 fill plug is located in the front housing.

The drain plug is at the bottom rear of the housing (Fig. 3).

Fig. 3 Drain and Fill Plug Locations

1 - DRAIN PLUG
2 - FILL PLUG