15 speed double OD

That's hard to put numbers on, after awhile you just feel it. Sorry that's best i can do for ya

 

Why the change in shift pattern for double over transmissions and what exactly does double over mean?

 

Funk, I think that statement referred to the 13spd trans only. Being that the 13spd was considered an OD, by switching the gears it made it a double OD. Alot of guys tried to do like the 10 and 9spds and just turn the shaft around to turn it intoa dbl OD but it wouldn't last long, the gears for some reason wouldn't match up right. To actually do it right it wasn't cheap as you had to change quite a few gears. This is what I was told when I had mine rebuilt, I ended up just leaving it a regular 13.

 

High gear being forward or against the dash in the shift pattern happens when the main gear on the input shaft is a larger gear than the next one on the mainshaft, which in turn speeds up all the gears in the box..
The shift forks in the top plate was redesigned on the RTX models, keeps it simple for those who can't deal with the gears being out of order, you know the steering wheel holders lol..

Direct drive means that the driveshaft from the back of the trans is turning the same speed as the crankshaft in the engine { 1 to 1 gear ratio }..
Any gear over that, { .087 } for example, is that much overdrive..
Double overdrive simply means that you have two gears that are over direct.. Usually refers to the RTOO 13 speeds, which have 3 gears that are overdrives actually, with high gear being something like .62..

Thats what I run and they do tend to heat up alot worse than the rest , especially if you don't have a cooler..

I'm sure somebody has done it to one somewhere, but for the most part concerning 15 speeds, they are not double overdrives, and trying to make one out of a RTO would really defeat the purpose in having a reduction trans to start with..

 

Interesting. Never though about it before like that. Thanks Gents. The truck I drive has a 13 double over, also has 3.90's and a Cat 16L. Pulls really well in the hills but still turns decent rpm at 65mph.

 

Ok. Is possible to put a axillary box on a 15 to the dash.Say you have 3:55sand tall rubber a heavy hauler.like the15 due to the deep reduction or super granny.Haven't had too much experience with the18s

 

When you say heavy haul, not sure how heavy your talking, but if your getting into situations to where you think you need a aux box, then you really should consider going to a lower rear gear. 3:90 would be a good start in my opinion.

 

My 89 Pete was new when I bought it.It had 3:70 rears 15 speed double over and would go over 120 mph. i sold it and then bought it back in 2014 .trans was changed but everything is the same now top end is 95 mph.trans number is the same including rpm between gears mph between gears.when I shift from 14 to 15 mph is the same 69 mph only difference is the top end. someone please explain this to me Eaton can't

 

Mack straight 15 underdrive top two

R and L through 5 flip into direct 6 through 10, then flip into top range for the 11 through 15 repeating the standard 5 speed pattern each time. The splitter sat on the low 1-5 and the mid 6-10 and then when you got into 11 and up you were above everything else in the transmission with the exception of the top two gears having underdrive. That means you back off the hammer a moment on a upgrade as you run out of torque and put it back down the floor. She will give you half a gear before you have to physically downshift to 14 and repeat.

It's much harder to write this out than to show you. It's not a pete, just a Mack 500 that we had. Not much for get up and go, but you certainly would get where you need to with 21 ton of stone in the box.

 

They made a direct and an overdrive version of the 15 speed (as far as I know there is no such thing as a double over 15). Its possible you originally had the OD version and the next owner swapped in a direct drive model. They made an RTO and an RTX shift rail assembly so it is possible to have the U-pattern or the H-pattern on either transmission.