overdrive reduction

Do all Warn Overdrives have a reduction of 25% (.75:1)? Just trying to figure out my reduction/speed/rpm with the T90A tranny and 5.38 gears.
Thanks,
Paul

One last thing, I posted a while back about calculating speeds with the tranny/tcase/tires/OD. I ran into an issue not knowing the gears for the T90A. Anyone have any additional info on how to know the gears? Herm rebuilt my T90A.

"I am finding conflicting info on several sites. Different gear ratios for the T90A and Dana 18. Novak lists the gears ratios as 2.79 first and 1.55 2nd. Herm rebuilt my T90 and his site lists the gears as 2.90 1st and 1.85 2nd. I found yet another indication 2.98 1st and 1.66 2nd. confusing".

 

The OD doesn't provide any reduction. It's 25% over, not under. Overdrive out = 1:1 in 3rd gear Overdrive in = 1:1.25 in
3rd gear with a 3 speed tranny. Same is true for 4th gear in a 4 speed. Can't help you on the T90. But I'm sure someone will.

 

I guess I did not use the right words. I meant a reduction in rpm via the 25% over. I have seen the .75 used around here. One of the questions though is using an online rpm/speed calculator.
1) the one from grimmjeeper asks for an underdrive in step 3. The Warn is not listed so I typed in .75 and got a number. I typed in 1.25 and get a different number for speed/rpm that does not seem to be right based on my experience driving it.

2) the online calculator from florids 4x4 asks for the under/overdrive and you have to put the number in yourself. I put in .75 not 1.25 for the same reason. Sound right?

Any help is appreciated.
Thanks,
Paul

 

.75 would be right for all of the overdrive units for a dana 18.

 

Correct gear ratios are relative to the specific transmission and transfer case vintage.

For your 1957 CJ the T90 A is (1st) 2.798/1....(2nd) 1.555/1....(3rd) 1/1
Your 1957 transfer case is 2.46/1

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