Since 1996, Quad 4x4 has been retrofitting 1989-'93 Dodge Turbo Diesel pickups originally equipped with the Getrag five-speed transmission with the newer NV4500HD five-speed transmission that is original equipment in 1994 and newer trucks.
|Complete 4x4 NV4500HD Conversion Kit features a brand new, current production transmission and all required parts to replace the original Getrag G360.|
When off-warranty 1989-'93 Dodge trucks with blown Getrags started coming in our shop in 1996, it was obvious a simple rebuild wasn't going to be the solution. These trucks came with a 7 year-70, 000 mile warranty which must have caused Dodge a fortune in transmission warranty claims because nearly 75% of these trucks we have seen had one to four transmissions replaced under warranty. With that kind of track record, you know the factory part just isn't up to the job. In addition, many of the parts required were not available and those that were had a gold-plated price tag.
Our inspection of failed Getrags revealed that excessive heat and insufficient lubrication were causing the transmissions to literally self destruct from bearing failure. At that point, I started doing research on the Getrag design and service procedures, looking for possible ways to modify it for better lubrication and cooler operation. My research showed the basic problem of premature failure with the gearbox was probably a combination of premature pilot bearing failure, use, bearing preload, basic design, type of lubricant and the power of the Turbo Diesel. We considered installing an external oil cooler and using synthetic lubricant. Our conclusion: while an oil cooler might prolong transmission life, we would still see bearing failures due to the modest size of the preloaded bearings; the use of a single tapered roller bearing on the front of the main shaft to handle radial, lateral and thrust loads; and drivers who would power up hills with heavy loads in fifth gear.
The only contributing factor to Getrag failures that is easy to remedy is the clutch pilot bushing. Why Dodge used a pilot bushing in the first place is a mystery, but a simple flywheel modification that any competent machine shop can perform permits the installation of a heavy duty, sealed ball pilot bearing.
|Broken stock clutch pilot bushing on left only lasted 44, 000 miles. It is strongly recommended you replace the stock bushing (a new one is shown on the right) with the heavy duty, thick wall QU51010 sealed ball pilot bearing (center). Flywheel modification is required.|
Our first thought was to install an older style four-speed with an auxiliary overdrive or installing a medium duty truck five-speed with adapters. These options may be viable alternatives, but high cost and supply problems made us decide to try the update to the NV4500 gearbox. Our first conversion took a week and utilized an adapter plate between the transmission and original bellhousing. Currently we are buying brand new, semi-finished bellhousings to adapt the NV4500 transmission to the Cummins engine.
The NV4500HD is a reliable and heavy duty transmission that is more than capable of handling the power of the Cummins engine. Early models had problems with retaining the fifth gear, but that has been taken care of by new mainshaft and nut designs. It is still a current production transmission, which means brand new units are available and affordable, plus service parts will be readily available for years to come.
The combined length of a new 4x4 NV4500HD and bellhousing is only 1/8" longer than a Getrag, so no driveline or crossmember modifications are required on 4x4 trucks. There is minor welding involved to reinforce the original transmission support plate and to modify the transfer case shifter to bolt to the new transmission. The weld-on pieces are included with the conversion kit.
The 4x2 conversion is a bit more involved. Cross member and propeller shaft modifications are necessary. We supply steel to weld to the crossmember as part of the kit. The 4x2 conversion also comes with a new transmission mount and rear output yoke for the transmission. Some 4x2 trucks will also need the speedometer driven gear replaced for proper speedometer calibration.
|4x2 NV4500HD with modified crossmember installed in a 1993 W250|
Included in all 4x4 conversions is a brand new, modified, current production NV4500HD transmission, new bellhousing with slave cylinder studs and pivot ball, clutch pilot bearing, clutch release bearing, transfer case input seal, transfer case adapter gaskets, adjustable transfer case linkage, Syntorq 75w85 synthetic gear lube for the transmission, transmission shifter, new floor plate, heavy duty transmission mount, made in the USA grade 8 hardware, 100 minute installation video, miscellaneous small parts, shop supplies, etc.. The primary components of the 4x2 kit are the same except of course the transmission is a 4x2 unit.
|(left) Getrag G360. (right) NV4500HD. Larger case of NV4500HD requires a new bellhousing to retrofit first generation Dodge trucks.|
The actual time required for an amateur mechanic to install the new NV4500, is probably around 15 hours. The conversion starts with the removal of seat and shifters. The new shift tower is farther back, so once the carpet is removed, a hole is cut in the floor to provide clearance for the new shift tower. Next, remove the drive shafts, disconnect the wiring, remove the transfer case, crossmember, transmission, bellhousing, and clutch components. The clutch assembly is a long-lasting (but somewhat "grabby" on take-ff) 13" Sachs/Borg and Beck unit which can almost always be reused, unless it has been subject to abuse or high (200, 000) mileage. If required, a brand new Sachs/Borg and Beck assembly is available as are a number of 12.4" and 13" South Bend performance clutches. The modified flywheel and ball clutch pilot bearing are installed after checking the rear crankshaft seal for leakage. Next is clutch assembly installation, then the new bellhousing and transmission. The original 4x4 crossmember is reused with the addition of a new heavy duty transmission mount. After the new transfer case input seal is installed, the transfer case is bolted to the transmission. One of our two styles of transfer case linkages is then installed, depending upon the year of the truck. With our kit, drive shaft modifications are not required, so finishing the underbody portion of the conversion requires simply replacing the remaining components and pumping the lubricants. The truck is then lowered for finishing the interior portion of the conversion which requires installing the new floor plate and shifter, relocating the transmission shifter boot, replacing the carpet, seat, and transfer case boot."
|First generation 1989-1993 Dodge turbo-diesel trucks have steel shell rear crankshaft seal pressed into an aluminum seal housing. Over time, the different expansion and contraction rates of the two metals will compress the seal shell. When this happens, engine oil starts to seep between the seal and seal housing. Replace this original seal before installing the NV4500HD. The QK6000 crankshaft seal kit includes the new design, Teflon lip seal with rubber sealing rings, installation tool, and video guide.|
The forward gear ratios of the current NV4500HD are slightly wider than the original Getrag. Reverse gear is slightly faster. (Gear Ratio Chart). Given the relatively narrow rpm band of the Cummins engine, does the wider ratio adversely affect performance? That was one of my main concerns when we started doing these conversions, but every customer that has commented on the gear splits tells me that they have a better spacing than the original Getrag. Everyone seems to like the lower first gear and the higher overdrive too. As a rule, NV4500's shift a lot nicer than the old Getrags.
The bottom line on retrofitting the NV4500 into '89-'93 models is that for about the same price as most Getrags can be pulled and rebuilt, the customer gets a stronger, more reliable, and easier shifting transmission.