Is it/would it be possible to put a GV Overdrive unit on a divorced T-case? I figure since I will need to move my NP205 up further then that the NP203 was, I should be able to put a GV unit on so I have overdrive with my Eaton FS5205. Anyone know if I am right or wrong??? I figure a fake 10spd would be fun.

 

you would need to put it before the case so that both axles got the reduction. No reason you couldn't put one before it, though. You'd just have to get the GV unit for the 2wd c6 and space the transfer case back to make up the difference. Or shorten the intermediate.

 

Not meaning to hi-jack your thread Jessie. Iwas wondering about the GV thing. If you have a C6 and the GV will that esencially give you a 6 speed tranny? If so would you be able to shift it under load like 1st low 1st high 2nd low 2nd high and so on? I know it's a crazy question but just something that got the curiosity thing going. Popa John

 

I agree with this.



Your understanding of the GV is correct here.

 

The one consideration though is that the GV unit needs the driveshaft to spin at a certain rate to be able to build adequate oil pressure to properly apply. The oil pump is driven by the input shaft, so to safely work, the typical ground speed needs to be in the territory of 45 mph. This will eliminate use at 1st gear to second. You also will find that the gears are already close enough that splitting the gears usually is not needed. You would shift out of 1st into 1st overdrive, then back out for 2nd, back in for 2nd overdrive, then back out for 3rd (Drive) then back in for overdrive. So while you do gain additional forward gears, but not really enough to make a difference. If you are towing exceptionally heavy or on a mountain, the split is useful. The rest of the time, not so much.

 

yeah, it would depend on how the gears split, but its likely that first high would be equal to one of the other gears, either 2nd or 3rd most likely. And etc so on through the gears. Would probably be way beneficial on a 3 speed but as you get up to 5 speed a bit less so. Always nice to have the overdrive on top if you do a lot of highway cruising and have the torque to lug along. I know the 6 speed 1999-2000 ish camaros had a super overdrive in 6th and they would do 70 mph at something like 1300 rpm and supposedly get mid to high 20's doing it.

 

I used to get 21 or so out of my 83 T/A with a 700R4.

 

Well I dont need it for both axles for the fact the truck is mainly going to pull a trailer some and pull sled so when I am pulling sled I wont need OD for both axles, so I would have the GV unit at the rear of the housing so I can use it highway driving. Cause I would like to keep the 5.13s that are in my D80 at the moment... IDK was all just a thought.

 

..going to follow this...I want to do the same thing to my 77 crew,..figured I would install the GV behind the t/f case and use it as an overdrive..let me know how it works for you..it is going to be awhile before I get to do it to my crew

 

Its gonna be a while before I do it lol I am strengthening my frame ATM

 

if you have the divorced case I don't really see any advantage to doing it that way, but thats up to you.

 

Cummins 5.9 with a Eaton FS5205 5 spd, which is a non O/D trans, with 5.13 rear gears... Umm yeah I see the usefulness. a O/D will let me at least have some sort of cushion on the Highway. Then I dont have to use the OD on the pull track so I can take full use of my 5.13's See the Multipurpose? Why and when would i ever need both my axles to be using the OD unit? 4WD will only be locked in on the track....

 

It comes down more to a location concern. On the back of the t-case will make for a pretty steep driveline angle. I can measure the length of the unit itself, but you will also have an adapter to be concerned with. I am afraid no matter where you mount it, things will likely need some relocation.

 

because you have a divorced T case. its just a 2wd trans with an intermediate shaft. Really no reason to put it after other than "just cause." also agree with the comment about driveshaft angles. Divorced t case is already a good bit longer than a married one. Add an OD to the back and youre looking at a pretty short shaft..

Plus you would have the situation where if, for any reason, you ever "forgot" it was in OD and shifted into 4wd you would break something. There have been lots of times the ability to grab the t case and knock it into 4hi has helped out a lot.

 

The GV unit is built & designed to BOLT to the output of the transmission, and is intended (even on divorced setups) to be between the transmission and transfer case.

The big problem is with torque holding ability. The GV unit is stout enough to take pretty good abuse and power. HOWEVER, think about this:

Assume a motor makes 300ft-lbs of torque at 2,500rpms.
In first gear with a 3:1 ratio, the output of the transmission transmits 900ft-lbs of torque. This includes the Gear Vendors unit, driveshaft, and the INPUT of the transfer case.

Ok, now put move the GV unit to behind the 205. Sure, you won't "use" it while you're in low range or 4wd. But, when you slide the transfer case into 2-lo, suddenly the rear driveshaft output jumps to 1,800ft-lbs of torque with our imaginary engine. If the GV (whether it's over driving or not) is behind the transfer case, it still has to transmit the full 1,800ft-lbs of torque through a gearset before it goes to the driveshaft.

Yes, you can do it, but why? You're radically increasing the chance it's going to blow up the expensive GV unit. Put it where the manufacturer recommends (bolted to the back of the transmission) and simply move the transfer case back a little bit to accommodate it. If you're already strengthening the frame to take the abuse of pulling, do it right the first time.

Another reason not to do it? U-joints. With the stock setup, you have 6 u-joints (or 7 if you have a CV front driveshaft) 2 on the intermediate shaft, and 2 on each driveshaft (or 3 if it's a CV). Putting the GV unit where GV says to install it keeps this exactly the same. Putting the GV unit BEHIND the transfer case would mean you'd need an extra intermediate shaft between the 205 and the GV unit, unless they sell one that mounts straight to the back of a 205 (and last I checked, they didn't). Extra u-joints would mean more chances of breaking things. If you're planning on using this as a heavy-duty sled puller (or towing heavy stuff) this is exactly what you DON'T want!

If I were building a puller, I would actually put a 4wd MARRIED GV unit into the truck, and then source a stock adapter/married 205 and simplify the setup down to 4 u-joints.