Reverse Divorced NP205 instead of Gear Vendors

[Boise Outlaw]

this is a hypothetical "what if". I know on the older trucks w/out overdrives its common to run a divorced t-case set backwards to have a higher final drive ratio. Question is would this be possible in our rigs with a little custom fab work, and could the np205 handle what the 7.3 deals out for power?

[glovemeister]

Why not get bigger tires, instead?

[351fifty]

pending on how much gear reduction you want, tires would be silly kause you loose one way by city driving with those, but i like the way your thinking, but how do you figure it would give some reduction to the gearing?

[Boise Outlaw]

i'm talking about running it backwards, the way a t-case is designed the output reduces the final drive ratio in 4 low, its what makes your tires turn slower at the same rpm. Flip that t case around and it will increase your final drive ratio, or make your tires turn faster at the same rpm.

This is the gear ratio of the e40d

1st = 2.71
2nd = 1.538
3rd = 1
4th = .712

and the np205 has a 1.96:1 ratio, so flipped backwards this would be your new ratio when you put the np205 into 4 low

1st = 1.38
2nd = .78
3rd = .51
4th = .36

You'd only really use it for distance driving, and probably never even use 4th gear unless you were really booking it.

[elrojo63]

I like the way you're thinking. Would you be doing this on a 2wd or trying to mount a second tcase to a 4x4?

[Boise Outlaw]

i have a 4wd and pretty sure the 4.10 gears, so having a higher final drive would make up for that. Basically you would need a custom intermediated driveshaft, t-case cradle, and shortened rear driveshaft. The shifter would probably sit somewhere under the rear seat in an ext cab.

I've done this before in my suzuki samurai (w/ the t-case facing the normal way). Its got an isuzu 2.2L diesel motor w/ 4x4 transmission and the divorced samurai t case behind that. When both t-cases are shifted into 4 low it has some serious crawling ability.

The only thing I would be concerned about with the np205 setup would be there may be an effect on the bearings wearing out quickly depending on how well it would lubricate itself running in the reverse direction.

[elrojo63]

if it would hold up, then that would be an awesome addition. I wonder how much of a PIA fabbing up something to work would be

[Boise Outlaw]

I think the t-case mount itself would be pretty easy, just find a 73-77 F250 with the divorced np205 and remove the whole thing including drivelines and mount, could probably even use the intermediate shaft as your intermediate in the new setup. If i'm really lucky maybe a 94-97 reg cab 4x4 8' driveline can be used as the shortened rear driveshaft. That would mean having to forego shortening and balancing the current rear driveshaft. Only custom work would be beefing up the t case cradle and cutting a hole in your floor for the shifter (ext cab) or just shorten the shifter and crawl under the truck every time you wanted it engaged. Probably add an oil cooler also for a little extra capacity and to keep your gear oil temp lower with the higher speed it is turning.


This is one of the forums that gave me the idea, ignore the stuff about running inline reverse transmissions

reverse transfercase- homemade overdrive - Ford Truck Enthusiasts Forums

Only concern they really bring up over there is the actual performance improvement. I'd say gaining 2-3 mpgs HWY could be justified, especially if you keep your cost low by only using stock junkyard parts. Say your total cost is $500 and you gain 3 mpgs HWY, that would mean that at $4 a gallon you would have made back your money after about 7k miles.

[elrojo63]

how about electric shift? for us guys with regular cabs and everybody who doesn't want another hole in the floor

[Boise Outlaw]

it looks like theres some guys out there that have converted the np205 to pneumatic shift, so with a little tinkering I'm sure you reg cab guys could figure it out.

Remember that all this is hypothetical, I havent sourced a parts truck or measured or anything else, I just know that if people are shelling out $3k for the Gear Vendors then there is definitely a need for a DIY version. I also dont know how well it would work with the auto tranny (which I have). With a manual there is alot more room for play in the gears, whereas with an auto you may run into issues with bogging out at certain speeds and would then have to add an electric shifter with computer override.