NV4500 - Manual Transmission

NV4500 - Manual Transmission / DESCRIPTION






The NV4500 is a five speed constant mesh manual transmission (Fig. 1). All gear ranges including reverse are synchronized. Fifth gear is an overdrive range. The transmission has a cast iron gear case and aluminum shift cover.

Two versions are used, a standard duty for 5.9L applications and a heavy duty for V10 and Cummins diesel applications. Main differences are the larger diameter input shaft, output shaft and mainshaft fifth gear in the heavy duty model.

Tapered roller bearings support the drive gear, mainshaft and countershaft in the gear case. Roller bearings in the drive gear support the forward end of the mainshaft. The mainshaft gears are all supported on caged type roller bearings. Drive gear thrust reaction is controlled by a needle type thrust bearing. The bearing is located at the forward end of the mainshaft.

The transmission is a top loader style. The shift lever is located in a shifter tower, which is bolted to the shift cover and operates the shift forks and rails directly. The shift forks and rails are all located within the aluminum cover, which is bolted to the top of the gear case.

GEAR RATIOS:

SHIFT PATTERN
The shift pattern is in a modified H pattern (Fig. 2). Overdrive fifth and reverse gears are in line and outboard of the first through fourth gear positions.








IDENTIFICATION
The transmission identification tag is attached to the driver side PTO cover (Fig. 3).

The tag provides the transmission model number, build date and part number. Be sure to reinstall the I.D. tag if removed during service. The information on the tag is essential to correct parts ordering.


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.