  The nice thing about owning a Jeep is that if anything breaks, some aftermarket company has already made a replacement part that will work better and last longer. 
That's the only thing that makes the failure of a part bearable. A failure gives
you the golden opportunity (and an excellent excuse) to upgrade a component. So it
was with the T4 transmission in our Scrambler. When the tiny transmission was
subjected to the torque of the Chevy 350, it immediately began to beg for mercy.
Six months later, third gear and the corresponding cluster gear lost several teeth
while accelerating on a freeway on ramp. (Click here for a close-up of the gears)After the Jeep limped back home, plans began forming for a transmission swap. Rebuilding the T4 was out of the question; we're confident we would have had the same fatal result in another six months. Besides, we wanted everything that the T4 tranny was not. We needed a tranny that was very reliable when coupled to a V8, we wanted a low first gear ratio, and we wanted an overdrive fifth gear. There is only one tranny that is easily swapped in to a Jeep that fills all of those requirements - the NV4500. The NV4500 tranny was introduced in 1992 in both Dodge and GM 3/4- and 1-ton trucks. The NV4500 has been used with both small and big block V8's, and the Cummins diesel in vehicles with a very high GVWR. This transmission should hold up extremely well in a lightweight Scrambler with a small block V8. Unlike the T4's all aluminum case, the NV4500 is made of cast iron and is physically much larger than the T4. Its size and heavy duty construction means the NV4500 tips the scales at 200 lbs; if you thought you could save some money by not using a transmission jack for installation, think again. From 1992-95, the GM version of the NV4500 transmission used a 6.34:1 first gear. This represents a 64% improvement over the T4's 4.03:1 first gear. Current Dodge and GM versions still use a respectable 5.61:1 first gear. As far as we were concerned, if we were going to go through the trouble of a tranny swap, we were going to use a GM NV4500 with the 6.34:1 first gear. All of the NV4500's use either a .73:1 or .74:1 overdrive ratio. Whether you choose a Dodge or GM version, these transmissions offer the best of both worlds in terms of gearing: a low first gear for slow speed off road work, and an overdrive for more efficient and much quieter highway travel. Since it was immediately clear which transmission we wanted to use in our Scrambler, we set out on the task of locating a used GM NV4500 with a 6.34:1 first gear. We didn't realize was how hard it would be to locate one of these trannies. These transmissions are a very hot commodity for salvage yards and don't stay in stock for very long. Rather than waste any more time fruitlessly searching the salvage yards in hope of saving a few bucks we decided to go straight to the source. JB Conversions is a one stop source for a complete NV4500 conversion, including all of the necessary adapters. A quick phone call to John White at JB got the ball rolling. Our completely rebuilt GM NV4500 with a 6.34:1 first gear ratio arrived within a couple weeks, with a factory Dodge tailhousing attached to mate our Dana 300, and a custom bellhousing to mate our 350. JB Conversions is the only source we're aware of that can readily supply a NV4500 with the 6.34 first gear. When we asked John where he was able to find the lower gears, he simply let out a chuckle. If you call him in search of one of these transmissions, don't bother asking him where he finds the gears; he (wisely) won't tell. At the moment, an NV4500 is in our Scrambler. The installation is not totally complete, however. There are still a few details yet to be resolved at the time of this writing. We'll let you know what difficulties we encountered during this installation and how they were resolved, and a complete list of the parts we used. We'll also throw in some installation photos for the next issue, as well as our thoughts on the driveability of this transmission, and address some cost concerns. Stay tuned! JB Conversions 132 Beauregard Ave. Sulphur, LA 70663 318-625-2379 
Dirt Road Magazine is sponsored by Turner 4WD Parts Co. |
