GV Overdrive unit on Divorced T-Case?
#16
06-25-2012, 11:30 AM
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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.
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.
#17
06-25-2012, 06:30 PM
It can go in either location in this instance. The majority of applications are married t-cases, so they don't really mention the divorced options.It doesn't directly matter if it is transmission mounted or t-case mounted. The one I have wasn't mounted to anything but the frame, as you can't directly mount it to a Dodge A518 transmission. It replaces the carrier bearing on that instance. The biggest problem I see with mounting to the transmission is the space. I'm not sure it will fit without relocating the t-case.
#18
06-25-2012, 07:27 PM
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Now lets ask this... How the sam hell would I get a GV OD unit on a Eaton Fuller FS5205? And has anyone ever installed it backwards on the input side of the T-Case? And Married T-Cases has the intermediate shaft and adapter go where as a Divorced one just may eat up jack shafts. You use big drive shafts and and big yokes. And don't tell me it wont work. Local cummins guy his old pulling truck was divorced T-Case and he would whipt he **** out of everyone easily..
#19
06-25-2012, 08:18 PM
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the GV can take some serious abuse...race cars use them instead of switching gears on the rear axle...I do know when I go and get my overdrive unit I am going to use it as an overdrive for highway driving so under/overdrive to my front axle means nothing in my situation, sounds like you are on the same page...
#20
06-25-2012, 08:26 PM
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the GV can take some serious abuse...race cars use them instead of switching gears on the rear axle...I do know when I go and get my overdrive unit I am going to use it as an overdrive for highway driving so under/overdrive to my front axle means nothing in my situation, sounds like you are on the same page...
#21
06-25-2012, 08:32 PM
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I once had a s/c w/ 4:10's up front and when the rear went I swapped in 3:50's ...more so to try the ratio..to see if it would work for me...along came an ice storm and I needed the 4wd....drove it...just a little squirrelly..
but it worked...but it took 'some' finesse to get it out of 4wd....so the different front and back ratios are doable..UNDER the right conditions
but it worked...but it took 'some' finesse to get it out of 4wd....so the different front and back ratios are doable..UNDER the right conditions
#22
06-25-2012, 08:42 PM
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#23
06-25-2012, 10:59 PM
Now lets ask this... How the sam hell would I get a GV OD unit on a Eaton Fuller FS5205? And has anyone ever installed it backwards on the input side of the T-Case? And Married T-Cases has the intermediate shaft and adapter go where as a Divorced one just may eat up jack shafts. You use big drive shafts and and big yokes. And don't tell me it wont work. Local cummins guy his old pulling truck was divorced T-Case and he would whipt he **** out of everyone easily..
On installing it backwards, I highly doubt that would work, plus, it would no longer function as an overdrive. The GV units are not a manual type overdrive, they require fluid pressure to work. The pump that supplies this pressure is driven by the input shaft, so if you try to run it backwards, the input shaft is no longer directly driven. It would become the output shaft.
#24
06-26-2012, 10:28 AM
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I have no idea on the Eaton, they only support light duty type applications. They state a HP max for their units.
On installing it backwards, I highly doubt that would work, plus, it would no longer function as an overdrive. The GV units are not a manual type overdrive, they require fluid pressure to work. The pump that supplies this pressure is driven by the input shaft, so if you try to run it backwards, the input shaft is no longer directly driven. It would become the output shaft.
On installing it backwards, I highly doubt that would work, plus, it would no longer function as an overdrive. The GV units are not a manual type overdrive, they require fluid pressure to work. The pump that supplies this pressure is driven by the input shaft, so if you try to run it backwards, the input shaft is no longer directly driven. It would become the output shaft.
#25
06-26-2012, 10:35 PM
I see exactly what you were saying - sorry it took so long to reply, I was at work 
If you're planning on putting it on a truck, and want to retain the possibility of swapping it to a married 205, then yes, get the one that replaces the output of the 205 and run it just like GV recommends. Then, if you want to swap to a truck with a married 205, you can swap the GV unit over. I had forgotten that the "married" 205 applications replaced the output of the transfer case, whereas the divorced setups went between the transmission and the 205. That's totally my bad! I also missed the fact that you're running a heavy diesel transmission - I was assuming a standard C6/T18 setup, which is pretty straightforward. I know that for Automatic Transmissions, the GV unit has a special box that usually automatically controls the engage/disengage - which would be a PITA when in 4wd if it were only on the output of the transfer case and the GV kept trying to engage/disengage.
I also didn't know that you never plan on having the truck out in the snow/salt/slop/etc. I run my 4x4's year round, and having the potentiality of a disaster occurring when I pull it back into 4wd scares me - that or the chance that I'd be overdriving the rear ratio in relation to the fronts - it would cause almost instant understeer and loss of control if you were in an appreciable amount of snow.
People who mud bog run different ratios in the front and rear - but they always run smaller gears up front - like a 4.11 in front and a 4.88 out back. This helps the front tires spin faster, and clear the mud from the treads, keeping the front end digging/climbing. If you spun the ratios around (or put an overdrive on the rear), you'd have rear wheels spinning/digging down into the mud, and a front end that just pushed without climbing. It wouldn't work very well!
I come from the Jeep world, where you try to mount everything (including doubler boxes for crawling ratios) before the actual transfer case - the further up the drivetrain you go, the less total torque the part has to be able to survive. If I had a divorced T-case, I would want the GV unit on the end of the transmission, and then simply move the t-case back slightly while shortening the intermediate shaft. HOWEVER - since you're running the HD diesel transmission, that's not an off-the-shelf option. Again, for what you're working with, mounting it on the output of the 205 is probably best. If you're already going to relocate the 205 a little bit, the new driveshaft angles shouldn't be as much of a problem. And, if they are, you can call Tom Woods or anyone else and they can make you a custom length driveshaft with a 1350/1410 CV that'll take all the abuse you can throw at it!
As for mounting it backwards to the input - pretty sure you can't do that. If you run a gearset meant for overdrive, but put the power through the output gear, you'll end up with an underdrive/reduction. Plus, if what everyone is saying about how the GV setup works, it requires the input to spin to provide hydraulic pressure to actuate the OD mechanism.
I would do like you were saying initially - replace the 205 output with the GV unit, as long as they say it can handle the torque from that Cummins!
If you're planning on putting it on a truck, and want to retain the possibility of swapping it to a married 205, then yes, get the one that replaces the output of the 205 and run it just like GV recommends. Then, if you want to swap to a truck with a married 205, you can swap the GV unit over. I had forgotten that the "married" 205 applications replaced the output of the transfer case, whereas the divorced setups went between the transmission and the 205. That's totally my bad! I also missed the fact that you're running a heavy diesel transmission - I was assuming a standard C6/T18 setup, which is pretty straightforward. I know that for Automatic Transmissions, the GV unit has a special box that usually automatically controls the engage/disengage - which would be a PITA when in 4wd if it were only on the output of the transfer case and the GV kept trying to engage/disengage.
I also didn't know that you never plan on having the truck out in the snow/salt/slop/etc. I run my 4x4's year round, and having the potentiality of a disaster occurring when I pull it back into 4wd scares me - that or the chance that I'd be overdriving the rear ratio in relation to the fronts - it would cause almost instant understeer and loss of control if you were in an appreciable amount of snow.
People who mud bog run different ratios in the front and rear - but they always run smaller gears up front - like a 4.11 in front and a 4.88 out back. This helps the front tires spin faster, and clear the mud from the treads, keeping the front end digging/climbing. If you spun the ratios around (or put an overdrive on the rear), you'd have rear wheels spinning/digging down into the mud, and a front end that just pushed without climbing. It wouldn't work very well!
I come from the Jeep world, where you try to mount everything (including doubler boxes for crawling ratios) before the actual transfer case - the further up the drivetrain you go, the less total torque the part has to be able to survive. If I had a divorced T-case, I would want the GV unit on the end of the transmission, and then simply move the t-case back slightly while shortening the intermediate shaft. HOWEVER - since you're running the HD diesel transmission, that's not an off-the-shelf option. Again, for what you're working with, mounting it on the output of the 205 is probably best. If you're already going to relocate the 205 a little bit, the new driveshaft angles shouldn't be as much of a problem. And, if they are, you can call Tom Woods or anyone else and they can make you a custom length driveshaft with a 1350/1410 CV that'll take all the abuse you can throw at it!
As for mounting it backwards to the input - pretty sure you can't do that. If you run a gearset meant for overdrive, but put the power through the output gear, you'll end up with an underdrive/reduction. Plus, if what everyone is saying about how the GV setup works, it requires the input to spin to provide hydraulic pressure to actuate the OD mechanism.
I would do like you were saying initially - replace the 205 output with the GV unit, as long as they say it can handle the torque from that Cummins!
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