Doug Nash OD Installed but...

[NCheek]

Well, I got my aux. transmission installed today, but upon test driving, it seems that I can't go any faster than I could before the installation. Unless something is wired up backwards, i think I might have an underdrive instead of an overdrive...

Not pointing any fingers, just trying to get this figured out. Is there any way for it to be some error of mine, or does the unit require different gearsets for OD vs UD?

Thanks.

 

[Greenie]

Does the tachometer indicate lower RPMs at speed?

 

[NCheek]

No, when it is in the lower of the two ranges, I can't reach the same speed that I could pre OD, when I shift it to the high range, it's like everything is normal again.

This is why it feels like an underdrive to me...

 

[sle2115]

Do you know a RPM/MPH range prior to install? Say you were running 60 MPH, what was the RPM? Now, Run 60 in OD and see if the RPM's are less/more. If they are less, it's an overdrive, if they are more, it's an overdrive. IIRC, when I calculated the RPM drop for my truck, it was like 750 at 3000 RPM, which should net some fuel savings. I don't have an overdrive, eventually, I plan on a ZF swap. (75:1 Gear Ratio = 3000 RPM X 25% = 750 RPM)

You can also use an RPM speed calculator online and get a good idea. You have to know the height of your tires, etc., but you can get close that way.

 

[david85]

You could swap 3.08 gears in there. That would give you satisfactory drivability with the underdrive and decent highway RPMs.

Either that, or look for an acutal overdrive....

 

[NCheek]

Do you know a RPM/MPH range prior to install? Say you were running 60 MPH, what was the RPM? Now, Run 60 in OD and see if the RPM's are less/more. If they are less, it's an overdrive, if they are more, it's an overdrive. IIRC, when I calculated the RPM drop for my truck, it was like 750 at 3000 RPM, which should net some fuel savings. I don't have an overdrive, eventually, I plan on a ZF swap. (75:1 Gear Ratio = 3000 RPM X 25% = 750 RPM)

You can also use an RPM speed calculator online and get a good idea. You have to know the height of your tires, etc., but you can get close that way.

I have a speed calculator made up on Excel, but I'm pretty sure it's an Underdrive because in the low range, I can't get to my normal highway speed, and in the high range, it feels like normal.

You could swap 3.08 gears in there. That would give you satisfactory drivability with the underdrive and decent highway RPMs.

Either that, or look for an acutal overdrive....

Both of those options have crossed my mind.

 

[sle2115]

Not sure about the Doug Nash, but if there is any clutches in there, you could be slipping them or something as well. I'm also not sure how the speedo is affected by the addition of the DN either.

 

[argve]

Depends on where the speed reading is coming from - is it on the output of the transmission or behind / after the 2nd tranny (DN)

 

[NCheek]

Not sure about the Doug Nash, but if there is any clutches in there, you could be slipping them or something as well. I'm also not sure how the speedo is affected by the addition of the DN either.

No clutches, just gears

Depends on where the speed reading is coming from - is it on the output of the transmission or behind / after the 2nd tranny (DN)

speedo reading comes from the rear of the Doug Nash unit, so it is accurate in either range. I am using my GPS for the accurate speed reading though...

 

[VanBoy]

I think the DN is the same thing as the US Gear axu. trans. I'm not sure that US Gear still sells the UD units.

Heck, there was a DN OD unit being sold on the local Craigslist for $500 about 3 months ago. I was tempted to get it (it was for a C6 though)- but I already have a GV on my C6.

Is there an id tag on the unit? Maybe it will say a ratio or something. If it's a OD, it'll list the OD ratio (I'm guessing .74:1 ratio). If a UD, it'll prob be backwards 1:.74.

 

[NCheek]

Jim at US Gear told me that the Dual Range portion of the company is not in operation, so no more OD/UD's. The only ID on the unit is a serial #. Th OD for these is 0.8:1 and UD is 1.25:1

 

[VanBoy]

Jim at US Gear told me that the Dual Range portion of the company is not in operation, so no more OD/UD's. The only ID on the unit is a serial #. Th OD for these is 0.8:1 and UD is 1.25:1

How long have they quit making the Dual Range...... did they say?

 

[trj]

Not installed backwards is it? ....just a thought.

 

[NCheek]

How long have they quit making the Dual Range...... did they say?

not sure, but I guess it was after the last corp. buyout...

Not installed backwards is it? ....just a thought.

Nope,, it has a yoke on the rear, and splines on the front.


On another note, there is an OD on ebay right now for a good price that I am eyeballing, but the adapter is for a th400 trans. I have already offer this proposal to Andylad13, so he is first in line, but if anyone wants to be a committed buyer of my fully functional Underdrive so that I don't break the bank if I were to buy the Overdrive, reply to this post or PM me. The auction ends in ten hrs, so its either goins to happen fast or not at all.

 

[NCheek]

Ok, Andlad13 is out, any other takers? DNe2 UD with adapter for thm400? 6hrs left...