18 Speed double over trannie ?

I thought an 18 spd was already a double over. May-be there are different configurations? I read something some time ago that 16th was one to one. Leaving 17th and 18th as over drives. I thought this was the advanage of an 18spd. Was I wrong?
greg

 

In an RTLO18918B the last 2 gears are the overdrive with a .86 and .73 ratio respectively. I run the exact setup you are talking about with no changes to the transmission. You aren't going to gain much by going to taller gears. At 67 MPH I turn 1350 RPMs. If you go taller than the stock .73 OD, every time you hit a little hump in the road you will have to downshift.

 

Desparado, sounds like he was talking about doing the old-school "turning the tranny around."

*piinngg, piinnnggg* "I got this stick up against the dash, I gotz to GO!!!!!" *beep, beep*

If I remember correctly, that speeds the whole tranny up; meaning that low and reverse are a little taller,too. I suppose you could also regear the splitter section from under/direct to direct/over like they used to be, but I don't even know if the RTLOs use the same splitter as the RTOs did. Either way, with that long an OD you're gonna be making some heat. I wouldn't do it without fitting all the coolers the heavy-haul spec trucks use.

 

All 13's and 18 speed tranny are 9 speeds with the back box added. To make a double over you have to turn 8th and 9th around.
If your truck has 3.36 rears you more thay likey never be in the "BIG HOLE" for its all ready geared to fast in the rearends.
Now if you had 3.70's, 3.90's, or 4.11's the double over works great, you'll had a speedy tranny with rear end that pull.
The "gear fast, run slow" idea came with these low RPM motors and thats why most every truck made today have 3.36 or less.

 

with 3.36 rears you wont have enough motor even if you have 1000 hp to run if he does that. leave it the way it is