i have a 99 f250 that i am trying to put a dt466 and a Eaton rt6610 in and i want i bigger final drive gear ratio than 1:1 and was thinking about putting a divorced np205 tcase in backwards but i still want to keep 4x4 and if it would be possible to move the 4x4 out put shaft to the back so when you reverse the tcase the 4x4 output shaft on the drivers side front and give me a .5:1 gear ratio with the tcase in low range and the transmission in 10th and when you put the transfer case in high range it would be a 1:1 final drive ratio so in the end i would have i high and a normal range which i would be fine because it rarely goes into 4x4 and i would have tons of torque with the 466 under the hood and don't really need a low range. wondered if that would be at all possible?

Ben McAdams

 

I am thinking better options if you go this route are either...

A - Do a twin stick conversion on the NP205. One stick is for Hi-Lo and the second stick with be for 2 or 4 wheel drive
B - Combine NP205 with the range box from an NP203 to build a "doubler" then you have 2 hi, 4hi & 4lo w/NP205 (can also be combined with twin stick to do what was stated above) and the NP203 range box will give you and ultra low option.
C - Go with an Atlas transfer case that you have 1:1, 2:1 & 4:1 outputs in either 2 or 4wd

 

Thoese are good ideas if I wanted to go slow but the problem is i want a higher speed and a lower rpm

Ben McAdams

 

Ah...I misunderstood.

In that case you might check out gear vendors overdrive, they offer a bolt-on solution that mounts to the output of transmission or transfer case. If mounted to a transfer case you will only have over drive in 2wd and it allows you to "split" gears, typically 2nd through top gear. 1st gear usually doesn't have enough road speed for it to engage. They also offer custom options but no idea what process is involved to order a custom setup.

Another consideration thinking about the first solutions I mentioned, since you would have options to have ultra lo, lo and high, you could go with different rear end gears that keep RPM down when you're in "high gear" 1:1 ratio, but if you need additional gearing to get a load moving you can start in low or ultra low depending on whatever setup you were using for transmission and xfer case.

Using a transfer case backwards I don't think would work very well. My thoughts are the gears are designed for moving a vehicle forward, they can go in reverse but at slow speeds, at highway speeds the gears might not hold up very well since you would be spinning the gears backwards of how they were designed to be used and inputting power on what was designed to be an output. That's just a guess on my part.

 

You can look around and find an RTO6610, which is an overdrive unit. There used to be overdrive kits available for those also. Don't know if they are still available, but, I expect you can still find one online.

 

I am not sure how well a transfer case would like to be driven from the output shaft. It would require a divorced transfer case and a bunch of driveshaft work in any case.

Other than finding an overdrive transmission, another idea is to put very high gears in the rear axle of the truck so that direct is similar in final drive to overdrive with a "normal" rear axle ratio. The Sterling 10.5 apparently came with gears as high as 3.08s at one time and currently can be had with as high as 3.31 gears, but finding anything aftermarket higher than 3.55 or 3.73 is not easy since apparently everybody wants lower gears to run large tires.

 

My '87 has 3.08s. Not high enough for a DT-466 B. Those engines turn 2800 rpm max. You can probably run around 70 with them, but be on the governor. Could put some big tires on to make up the difference and use 3.08s.

 

Yeah 35inch tires is the biggest i want to go but I want to be capable of 75mph and a lower rpm. The picture is gear ratio, tire size, rpm and transmission gear ratio =speed

 

Yeah 35inch tires is the biggest i want to go but I want to be capable of 75mph and a lower rpm. The picture is gear ratio, tire size, rpm and transmission gear ratio =speed. And 2200 is about as I would be comfortable with over long periods of time

 

https://www.powerstroke.org/threads/...endors.237571/

this is where i got the idea but i want to keep 4x4 without having to install 2 transfer cases, the one in front for 4x4 and the one beind that backwards and when I would put the front one in 4x4 I would pull the back one out low and In to high

 

There were a couple valid points brought up in that thread why this may not work so well.

The splash oiling system may not work correctly since the transfer case will be working in reverse, if that's the case the bearings and gears will have a much shorter life.

The second thing was in order to shift into 4 low (redneck overdrive in this case) you have to be at a full stop. If you're trying to get going with a full load you may not have enough​ gearing to do so in when you're engaged in "overdrive"

You could compensate for that by putting taller gears in the the differentials but by the time you add all this up cost and labor wise and the likely event of failure using the transfer case well outside its design parameters I think you'd be much better off sourcing a proper overdrive add-on or transmission with overdrive.

Interesting thought exercise none the less.

 

Are you going with a 466-B? They will run 2200 all day long without problems, I've owned two mid-80's DTs that worded 5 days a week. They were constantly changing gears at governor limit rpms delivering heavy loads all day, then at high idle while pumping off at each stop, then on the governor when on the interstate. One had at the high end of 300k and the other 160k when I sold them. Never any problems at all.

These were heating fuel oil delivery trucks, so they weren't pampered.

 

Yeah I get the oiling issue would be a gamble but I think starting with a load wouldn't be to hard the rt6610 has a first gear ratio of 8.94:1 and take off .51 would be 8.43:1 i think would be ok and if I'm towing a heavy especially in hills i would stop and shift the transfer case in high and just go slower with a 1:1 od gear ratio.
and as far as what the engine will handle I could run the governor long and hard and it most likely will hold up very well with the reputation that engine has made but I would like to play it safe and hope it's nice back.

It is a 85

 

If I'm doing my math right, 8.94:1 first gear, being reduced/multiplied by .51 in the transfer case would result in 4.47:1 first gear. You can't just subtract .51 from 8.94, gearing multiplies or divides what is input.

For every rotation of drive shaft going into the transfer case (now reversed) the output shaft would only make about half a rotation.

8.94 x .51 = 4.47:1. For final drive ratio you'd need to multiply by your rear gear ratio.

 

Oh I dont know what i was thinking that make a lot more sense yeah with a load that would be a problem