The NV4500 manual transmission is highly sensitive to its fluid type as it uses special carbon fiber synchronizers. The original fluid spec is Castrol Syntorq synthetic 75W-90 GL-4 manual transmission fluid. Castrol's fluid is difficult, if not impossible to locate (it may be discontinued), but both General Motors and Chrysler continue to sell the formulation under their own brands. The Chrysler part number is 12346191 and the GM part number is 4637579. While the ACDelco fluid is spec'd as a 75W-90, the MOPAR fluid is actually listed as a 75W-85; both are suitable fluids for the NV4500. Amsoil 75W-90 manual transmission fluid is a popular, more affordable alternative to the relatively expensive OEM oils. Do NOT confuse Castrol Syntrax and Syntorq.
The Dodge and General Motors versions of the New Venture NV4500 are slightly different, with the Dodge unit marketed as a heavy duty "NV4500HD". For all intents and purposes, the operation of the transmissions remains the same, as are the service procedures. However, for the sake of following OEM recommendations, we would recommend obtaining GM fluid for a GM NV4500 application and MOPAR fluid for a Dodge application; or reduce the impact on your budget and go with Amsoil's alternative.
The Dodge NV4500HD commonly suffers from a loss of 5th gear, where it becomes physically impossible for a driver to put the transmission into overdrive - this problem is extremely rare if at all existent in GM applications. The cause of such failures has been attributed to frequent lugging of the engine; high load, low speed situations. Towing in 5th gear at 1,000 rpm, for example, should be avoided in order to prevent such occurrences. Proper transmission service will not prevent, alleviate, or eliminate such failures as driving behavior alone is to blame.
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• Place the transmission in gear and set the parking brake.
• The NV4500 has PTO provisions on both the driver and passenger sides, while the fill plug is located on the passenger side.
• Place a suitable container below the transmission to collect the fluid. Remove the bottom bolt from the PTO cover with a 9/16" socket; allow fluid to drain completely.
• You may drain the fluid via this single PTO cover bolt, or you can remove the entire PTO cover. We choose to remove the entire cover, which allows us to soak up fluid in the sump of the transmission that will not drain through the PTO bolt hole, as well as give us the opportunity to inspect for metal particles or debris. If you choose not to remove the cover, you can simply replace the PTO cover bolt and fill the transmission with fluid after it drains, skipping several of the following steps.
• With the cover removed, soak up any remaining oil that has settled in the sump of the transmission using a lint free rag.
• Thoroughly clean the mounting surface of any sealant, then spray a lint free rag with a solvent (brake cleaner, carb cleaner, etc) and wipe the surface clean of any oil. Do not spray solvent directly onto the surface. Do not allow any debris to enter the transmission.
• Thoroughly clean the PTO cover of any sealant, oil, dirt, and debris.
• Apply a continuous bead of oil resistant RTV silicon along the perimeter of the PTO cover (~ 1/4" wide will suffice).
• Reinstall the PTO cover; torque bolts in a cross pattern to 30 ft-lbs. Allow sealant to cure per manufacturers specifications before continuing (24 hours is common if a cure time is not listed).
• Remove the transmission fluid fill plug using a 3/8" Allen wrench/socket.
• Add transmission fluid until it reaches the fill hole level - when fluid begins to spill out of the fill port, the transmission is full. Most auto parts stores sell a convenient adapter that turns an ordinary oil quart container into a fluid pump. Reinstall the transmission fill plug when full. See fluid information above; only use a suitable fluid as discussed above or transmission damage will occur.
• Drive vehicle, allowing transmission to reach operating temperature and check for leaks.