Reversed t-case as "overdrive" unit

[patracy]

Just kicking an idea around in my head. But what about taking a divorced NP205 from a older dodge or ford pickup. Gut the "front" output shaft and gears out of it. Then install it backwards between the transmission and t-case of the deuce. You'd effectively double the the output shaft speed. going into the t-case. The NP205 is a cast iron lump that's known for it's stoutness. You could probably get away with using a gear box from a NP203 too. I know you can't shift them on the fly from low to high. But we could shift our rockwell cases from low to high if you wanted to tow with it in "overdrive".

Just thinking out loud really. Any thoughts/feedback?

 

[appalacious]

So, would you normally drive with the rockwell in 'low' then? and then at highway speed shift it to 'high'? What if you wanted the really low granny that the rockwell normally gives? I guess then you could stop and shift the np205 to low?

probably lose a little horsepower, but might be worth it?

This seems like one of those things that sounds great to newbies like me, but its about to get shotdown by old farts who know too much.

 

[jwaller]

just buy the OD gears and be done with it.

 

[appalacious]

wait a sec, if the np205 is backwards, that means it's got to be in "low" to get that high gearing. so you'd shift it to 'high' to go back to the really low gearing the deuce is normally in.

ok, i think i got it now. whats the ratio of the np205 high vs low?

 

[patracy]

So, would you normally drive with the rockwell in 'low' then? and then at highway speed shift it to 'high'? What if you wanted the really low granny that the rockwell normally gives? I guess then you could stop and shift the np205 to low?

This seems like one of those things that sounds great to newbies like me, but its about to get shotdown by old farts who know too much.

My thoughts would be, have the t-case "overdrive" it it's "low" range (which with the case backwards would be an overdrive effect). It would effectively cut engine RPM's in half though. So it'll be very tall with the gearing. You could easily use the low range of the deuce's rockwell t-case to start out with though. Then pop it into high range when you get up beyond highway speed.

I'm running stacked t-cases in my little diesel suzuki samurai. The concept is the same, only you're fipping the t-case backwards for an overdrive effect instead of the traditional underdrive effect.

 

[appalacious]

is there any advantage to having it between the tranny and rockwell t-case? why not put it after the rockwell?

 

[patracy]

just buy the OD gears and be done with it.

$1500 + dropping the transmission + R&R for the gears + reinstall the transmission + gear oil. Or less than a grand for what I'm talking about?

 

[patracy]

wait a sec, if the np205 is backwards, that means it's got to be in "low" to get that high gearing. so you'd shift it to 'high' to go back to the really low gearing the deuce is normally in.

ok, i think i got it now. whats the ratio of the np205 high vs low?

Yes, that's exactly what I'm talking about. The NP205 and the NP203 gearbox have a 1.98:1 reduction range.

is there any advantage to having it between the tranny and rockwell t-case? why not put it after the rockwell?

You could place it afterwards, but there's a few things to consider. You can't have it in 6x6. Sprague trucks can't run it. And the effective torque load would be doubled to that "light duty" t-case when the rockwell t-case is in low.

 

[73m819]

Dont think there is room between the trans and xcaes, if you put it behind the xcase, if you are not carefull, you will have TWO different gear ratios going to the f/r axles, this will = BANG

 

[patracy]

Dont think there is room between the trans and xcaes, if you put it behind the xcase, if you are not carefull, you will have TWO different gear ratios going to the f/r axles, this will = BANG

Wish I still had that NP205 laying around. I'd measure the flange to flange length. Anyone know off the top of their heads the intermediate shaft length on a deuce? We could easily shorten the driveshaft to the tandem axles if the rockwell case needs to be moved back a hair. The front shaft would of course have to be lengthened.

I know the NP203 gearbox is about 6" in length.

 

[jwaller]

$1500 + dropping the transmission + R&R for the gears + reinstall the transmission + gear oil. Or less than a grand for what I'm talking about?

1. it's not that expensive
2. you get a rebuilt trans in the end
3. there is only about 8 inches between the trans and xcase in deuce and your 205 wont fit and still leave room for the u joints.
4. there is no way that 205 will take the abuse it was never designed for in a backwards configuration. doesn't it only hold about a quart of fluid?
5. the gvw the 205 came in is about 5000bs right? can'the deuce max out at about 22000?
6. All the time and effort and work of making what your talking about is worth something? I bet it's less than the difference in the gearset.

 

[patracy]

The 205 wouldn't fit, but the 203 gearbox is only 6". Again the cases could be moved and driveshafts adjusted accordingly. If you were to gut the 205 case, you'd gain another quart of fluid capacity I'm sure. You are correct about the weight. The 205's and 203's were in trucks that tipped the scales at 6-7k lbs. But the torque output from a multifuel is only ~330ft-lbs. These cases are known to stand behind big blocks pushing that much torque or more.

So how much are these gearsets for the transmission? There's a thread here I've followed and went to the member's site, but the pricing showed about $1500 for the gears.

 

[clinto]

1. it's not that expensive
2. you get a rebuilt trans in the end
3. there is only about 8 inches between the trans and xcase in deuce and your 205 wont fit and still leave room for the u joints.
4. there is no way that 205 will take the abuse it was never designed for in a backwards configuration. doesn't it only hold about a quart of fluid?
5. the gvw the 205 came in is about 5000bs right? can'the deuce max out at about 22000?
6. All the time and effort and work of making what your talking about is worth something? I bet it's less than the difference in the gearset.

I was going to write a long rely, but jwaller covered all the points I was going to cover.

A 205 is designed, at most, for one ton duallies, not 2.5 ton 6x6's.

And regarding point 6, I think this is dead on. It isn't going to fit between the trans and transfer and if you put it behind the transfer, that's going to be complex, what with the parking brake, driveshaft length, air tanks, etc. to be dealt with. I think it's one of those things that is "simple in theory, but complex in execution".

 

[tm america]

It's not gonna work like you think...yes that would double your gear ratios..but the mutlifuel doesnt have enough hp or torque to take off from a stop if you doubled the gear ratios you would have to use low.This would give you the same ratios as stock in high...Then you would need to shift the 205 to low and trans to like second or third while moving.....Here's where the won't work comes in....The 205 is not syncronized like the stock deuce t case.so it can't be shifted on the fly....and what if you do all of this ,and find out there are no more useable ratio cuz the multi won't pull that much ratio drop at highway speeds.oh ya you would have to move the transfer case back to fit it in there which means all new driveshafts$$$$$$$

 

[appalacious]

doesn't the preferred overdrive gear replace another gear?

 

[patracy]

Wasn't that hard to make a underdrive unit for my samurai. Course the alum welding was farmed out. The main work for this would be mounting everything. But the frames are so simple on these trucks. Just some thick wall C-channel would work for a crossmember. Since the NP205 comes in a divorced setup from the factory. One could "cheat" and just use flat flanges on the input and output. Then have the flanges surfaced flat and re-drilled to the flanges off the rockwell case and deuce's transmission. Then couple them directly to each other. Of course this would require solid mounting the t-cases, transmission, and engine in the frame. But that'd be the "cheap" way out.

I'm just applying a concept that was used in the past in the samurai. The samurai has a divorced setup from the factory. There was a company that took a set of gears from a sidekick and placed them into a custom billet housing. This housing then had a slip yoke on one end and flange on the other. It was swapped in place of the factory intermediate shaft. It's no longer produced since the billet housing was so costly. And it's cheaper to just run a sidekick transmission, hack a sidekick t-case, use a coupler on the output shaft of that to couple it with the stock samurai t-case with a steel "housing" between them. It's the same concept of this, only in a larger scale and backwards.

 

[patracy]

It's not gonna work like you think...yes that would double your gear ratios..but the mutlifuel doesnt have enough hp or torque to take off from a stop if you doubled the gear ratios you would have to use low.This would give you the same ratios as stock in high...Then you would need to shift the 205 to low and trans to like second or third while moving.....Here's where the won't work comes in....The 205 is not syncronized like the stock deuce t case.so it can't be shifted on the fly....and what if you do all of this ,and find out there are no more useable ratio cuz the multi won't pull that much ratio drop at highway speeds.oh ya you would have to move the transfer case back to fit it in there which means all new driveshafts$$$$$$$

I mentioned the fact the NP205 and 203 gearsets are not syncronized in the past. That's why I mentioned one would simply lock it in "overdrive" and use the rockwell case in low to start out with. Then pop it into high range when up to speed. You are right though, I'd imagine the multifuel doesn't have the grunt to pull with that ratio now that I've looked at the math on it. (BTW, shortening driveshafts isn't that expensive.) Guess I'll look around more for a more suitable candidate with a narrower "overdrive" ratio. I would be easy to come up with a small box with a plantery gearset in a fixed ratio. But the downsides would be that you'd locked into that taller gearing and it affects all gear ratios.

 

[docfarmall]

I say try it with the abuse i put my old 1 ton ford thru it was as tough as my duece only diff i got more brakes now those transfers granted are in smaller trucks but will take more abuse than you think ever pull 11 rail cars with a 1 ton ford stock 7.3 i have and the transfer is still in that truck that truck is still on the road with well over a million miles on it yes the transfer will stand up .

 

[73m819]

Wasn't that hard to make a underdrive unit for my samurai. Course the alum welding was farmed out. The main work for this would be mounting everything. But the frames are so simple on these trucks. Just some thick wall C-channel would work for a crossmember. Since the NP205 comes in a divorced setup from the factory. One could "cheat" and just use flat flanges on the input and output. Then have the flanges surfaced flat and re-drilled to the flanges off the rockwell case and deuce's transmission. Then couple them directly to each other. Of course this would require solid mounting the t-cases, transmission, and engine in the frame. But that'd be the "cheap" way out.
.

This wont work, HAVE to have the slip joints because of frame flex, you bolt everything rigid with the cross members, you WILL BREAK a bunch of something

 

[stumps]

... One could "cheat" and just use flat flanges on the input and output. Then have the flanges surfaced flat and re-drilled to the flanges off the rockwell case and deuce's transmission. Then couple them directly to each other. Of course this would require solid mounting the t-cases, transmission, and engine in the frame. But that'd be the "cheap" way out.
.

The frame in the deuce flexes enough that it was necessary to use springs to mount the box! If you leave out the universal joints, you will break something.... At the very least, use an appropriately sized lovejoy coupling.

And after all of that, you will discover what those that drive deuces already know: They barely have enough HP/torque to get up hills in 4th gear, let alone 5th. Add a 2:1 overdrive, and you're sunk if you can't shift it out on the fly.

Also, the gearing in the typical low range of a transfer case is intended for walking speeds. They are horrifically noisy when you try to make them go fast. The deuce is loud enough already.... and you will be driving the gears backwards, to boot... not a recipe for long life.

One of the most unsettling things about using a deuce on the road is traffic lights. I have more than once started when the light turns green, and just about cleared the intersection by the time the light turns red. There is a lot of weight to get moving, and a very small engine... You definitely don't want to toss a 2:1 OD on top of those lower gears!

Give M35Tom the business and buy an OD gear set from him. He'll be thrilled, you will be happier with the ratio, and you will get a well tested product for a reasonable price.

-Chuck