Air ride cut off with 2.64 Meritor rear ends

Go to an RT12515 or 14615 and you might be ok. The RTO isn’t gonna have enough low hole. Personally I’d install it cause he bought it and swap the chunks for what he needs.


A lot of them ol big cams were 4:11 with a direct 9. 3:55 was a tall gear for em with a direct 9. So 2.64 well…

 

Why would the 15 direct not work for you for what you do?

Higher rears need less over drive at road speed and more reduction to get rolling. A 15 direct is lower geared all the way around than a 15 over so again why wouldn’t it work.

2.64 rears a 1.1 trans and 24 talls is 81mph at 1800 RPM. Exactly how fast you want an old binder to run? The problem you’re gonna have is lifting in soft dirt and the side load from that big ### pinion. Above is a ratio chart for a 15. Higher the number the lower the gear or more reduction. A 15 direct has more reduction than any other trans beside a 2 stick. You’re gonna need that on a gutless big cam.

 

I can figure it but rather not I can tell you from experience it’s really close. But you are correct that it’s better to go lower out back not running the boulevard. Reason I say that is the higher your rears the more teeth is on the pinion. The more teeth the pinion has the farther away from center the ring gear has to sit on the carrier. This causes a side load effect from simple leverage. Now with 90k in the hopper and 16.94 reduction something is gonna move. Be it the load intended, the drive line twisting or the differential carrier ####ting it’s self out the back of the housing. If you were staying on hard surface I’d say you’re probably ok with the high rears and direct. However I will say if you decide to go high rears and an RTO you’ll hate that m’fer

 

I run 2.74s on tall 24.5 was on a 15 speed to begin and now an 18spd, I cruise in direct at a little over 1500 rpm's at 73 mph, if I am not at highway speeds I am down in 15th or 14th gear which is kinda messes with your head at first, I have a c15 if it was a mechanical I would probably spend alot more time in 15th 15th at 70 mph is right at 1700 rpm, the truck pulls effortlessly at this speed, You just have to get used to not using your overdrives. The one thing I will say is if you are using it as a farm truck taking off loaded on soft ground I wouldn't keep those gears, you are going to end up damaging driveline stuff, it is a pain getting going on real soft ground and hills, and are going to end up breaking stuff, defeating any fuel mileage savings you see from the gears, my truck is a highway princess and the gears work good for me.