It was, without question, the best manual tranmission option that Dodge ever offered for a Cummins, V10 or V8. The input shaft, front retainer and output spline count are the only differences on the Dodge versions. The Chevy versions used a longer tailshaft that was 32-spline, the Dodges were shorter and either a 23 or 29 spline depending on the original application. Internals, with the exception of the early Chevy versions with the crazy-low first gear ratio and fith-gear retention hardware (Dodge only), were all identical. And yes, "bomb proof" would adequately describe a tranmission that can handle a Cummins 6BT that makes 800+ pounds of torque. To say otherwise makes me wonder if you have it confused with the little sister, the NV3500, which was a turd pile.
No, I'm certainly not confused. I have overhauled many, many NV4500's. I've seen more than I can count ripped apart behind 500 lb/ft 5.9's with stock clutches. I've installed more than a dozen Torque King mainshaft and 5th gear sets and seen every other style of 5th gear retention fail. I did this work as side income when starting a machine shop for local hotshot guys. A close friend owns a diesel repair shop. I did all his stickshift transmission benchwork for several years. In the time period I did this work a 5.9 Dodge with an NV4500 was the primary vehicle employed for hotshot type work. I was busy with NV4500 repairs.
I have machined custom mainshafts for NV4500's, switched gearsets and ratios. mixed and matched GM and Dodge parts to create custom versions and I still have to call experts at transmission parts houses with questions on occasion.
There are three completely different cluster gears for NV4500's, not two. The early GM, the early dodge and the late dodge. The late cluster gear set coincided with the top plate change. These parts do not interchange.
There is a significant difference in the diameter of the mainshaft from the standard duty NV4500 to the HD version. This is not regarding the output shaft splines, but specific to the size of the shaft inside the transmission. The HD NV4500 requires a different socket to remove the 5th gear nut.
A good 5 speed transmission behind a 5.9 Cummins is an FSO Fuller.
I agreed the NV4500 HD is a reasonable transmission behind a 5.9 on the grounds that when they do break parts are dirt cheap for them and they are easy to work on with only a few special tools. The NV5600 is an engineering disaster. The G56 isn't a bad design, but parts are beyond ridiculous for them.
IMO, the Ford ZF 6 speeds are miles ahead of any of the other diesel pickup offerings. The ZF is a good design, it's engineered well with service and rebuilds in mind, the size of the parts inside is in accurate proportion for what they should be to handle a 350HP diesel engine. The shift quality is fair and quite good when you're aware of the mass of the parts the stick is moving inside.
NV4500's are not bad, in the overall scope of transmissions to put behind a 5.9 Cummins an NV4500 with a few thousand in upgrades assembled properly will handle quite a bit. A stock one is atleast cheap to fix when it breaks.
Sorry for cluttering the thread. I just don't see a significant advantage to a light duty NV4500 over an H55. I think with the right gears and tires the H55's short overdrive will actually be pleasant, not disliked. I have driven a number of 4BT converted vehicles with Mazda M5R2 5 speeds including a 60 series Landcruiser and the overall performance was excellent. The M5R2 has a similar short 5th gear.
