In the words of Ricky Bobby, I wanna go fast! Well, at least the speed limit. These military trucks were only designed to go convoy speed, which is only 55mph. I think the truck shifts into it's 3rd and final gear at 32-35mph. So at 40mph it will get 25mpg, which is great. But who wants to drive down the highway at 40mph? at 60mph, that fuel economy drops down to around 18 mpg. At 70mph, with the engine redlining, I don't want to know. 9mpg? It be nice if we could go 65mph, with at least 20mpg, and the engine somewhat quiet so two can have a conversation in the cab.
Sure, there are a few solutions.
#1 Man up and deal with it.
-I guess I lost my man card when I lost my hearing from the screaming engine.
#2 Change the speedometer gear to a different ration so it says the truck is going faster than it really is.
-This would be great if someone did it and never told me about it. I'd just assume everyone passing me is just really really speeding.
#3 Swap in an electronic 4L80E transmission.
-Too much work just to be stuck with another automatic.
#4 Actually man up and drop in a manual transmission with overdrive, like a NV4500.
-Now we're talking! If only the engine was old and no good, then we could throw in a Cummins 6bt! But really, with the whole pto generator setup, I really just don't want to mess with that stuff because it just works and it's awesome the way it is.
#5 Find another way to get overdrive.
They sell bolt on units to get this extra gear. But they aren't cheap...
But hey, can't beat free! It's a Gear Vendors overdrive unit, fresh out of the garbage! This unit came out of a Ford van, so it's not exactly going to bolt right up. But we can make it work. This unit will automatically engage around 45-50mph, giving us that nice, relaxing overdrive that everyone with newer vehicles keep raving about.
First thing to do is see how we're gonna attach this thing. It bolts to the back of the transfer case, so we took that out. Here you can see the back of the TH400 transmission.
The old overdrive is going to have to be taken apart. The old adapter is useless, will need new one for the NP205. We're even teaching the local youth all about auto mechanics and drivetrain components. It's good to start them early.
Here is the NP205 transfer case we removed. You can see in the lower right hand corner, the pto for the generator. In the upper right hand corner, there is the new adapter needed to mate the overdrive to the back of the NP205.
One big hiccup we ran across is that the overdrive only bolts up to a fixed yoke NP205. This truck has a slip yoke NP205. Well, we can fix that too, just need to open up the case and change out the rear output shaft. Don't need the rear housing or yoke or anything because the overdrive bolts right up to the back of the NP205. Found this used output shaft on the interwebs, should be an easy replacement.
Don't lose these!
Old slip yoke shaft...
New fixed yoke shaft...
Now we just gotta get this giant thing back into the truck...
Well, it fits, barely. Due to the added length of the drivetrain, the outputyoke for the driveshaft almost hits a bracket for the generator belt. It should probably be fine.
eepwall:
Had a driveshaft laying around. Got it cut down to the right length and bolted her up. Here's a video of the whole thing bolted and wired up, and some unexpected guests came to see what was going on.
https://www.youtube.com/watch?v=4CCIBmLDj-Y
