Looking around for these NV4500s. Price seems to be $900-1000. Is that right? if I was to go down this path, am I looking at major issues with finding the appropriate bell housing, transmission mounts, other mechanical stuff? Sound like some of you guys have experience with this. Is it a simple swap, like the rear pumpkin?
Tom
You need to find a 1994-1997 Dodge 2wd NV4500. A newer Dodge NV4500 can be made to work, but it you will have to get a digital to analog converter for the speedometer.
Why the dodge NV4500, and not the GM NV4500?
The early dodge version can work with a Mechanical speedometer. The pilot shaft of the dodge unit is 1 inch longer than the pilot shaft of gm unit. Since there is no version that will bolt directly up to a stovebolt bellhousing, a 1 inch adapter plate is used. By using an adapter plate, most of the stock clutch components can also be used.
The NV4500 swap is still not quite a drop in swap. Additional machining is needed to bolt it all together. The adapter plate that Advanced Adapters sells is indexed for a bellhousing with a center hole of 5.125 inches. The bellhousing on your 270 is indexed to 4.686 inches. What this means is you either have to turn the indexing lip down on a lathe so it will fit your bellhousing, or have your bellhousing bored out so it will fit the adapter plate.
Next is the bearing retainer on the transmission. The throwout bearing rides on the bearing retainer of the transmission. The Dodge bearing retainer collar is a little wider than the sm420 collar. This part can be removed from the transmission and cut down on a lathe so the stock throw out bearing can be used. You may be able to use a crossover bearing and avoid this extra machine work. I machined mine so I could use off the shelf parts and still look it up by the year and make of my truck.
A custom pilot bearing will need to be used. This will be a bronze oillite type bushing. The Dodge NV4500 has a pilot tip of 0.750 inches. The sm420 you would be replacing has a pilot tip of 0.590 inches. The ND7109 ball type bearing you currently have will not work for this. So the pilot bearing is the only clutch component that has to be changed.
The Dodge NV4500 comes with either a 10 spline 1 1/8 pilot shaft, or a heavy duty 10 spline 1 1/4 pilot shaft. You want the 1 1/8 pilot shaft as that is the same pattern as the sm420. If you find the heavier duty diesel transmission, the pilot shaft can be swapped. You will also need to swap the bearing retainer for the lighter duty gas version. If using the 10 spline 1 1/8 pilot shaft, the stock clutch disc and pressure plate can be used.
The shifter for the sm420 is centered about 4.5 inches from the front of the transmission. The shifter for the dodge NV4500 is centered about 10 inches from the front of the transmission. When using a 1 inch adapter plate, the shifter will be pushed back approximately 6.5 inches from where it currently is.
The NV4500 is a longer transmsion than the sm420. You will likely have to have a driveshaft made. It may be possible to get rid of the 2 piece drifeshaft and have a single piece driveshaft made. I have a 59 1/2 ton long bed and was able to have a single piece driveshaft made.
Lastly, a transmission tail support will be needed. I had a local metal shop fabricate a crossmember for this purpose.
John
PM me if you have any questions. I'd be happy to answer any questions over the phone.
