Double over 13

Every new 13 or 18 are double overs. One is a .86 and the other is a .74 like any 10 speed od on the road. In the old days you only had the .86 and 12th was direct.

 

Keep in mind engines have a parasitic load that drains some of the availible work before it reaches the transmission. If I have to be afraid of anything it's a cheaply spec'ed drive shaft that intentionally fails before the final drive takes damage.

 

if your flinging driveshafts and breaking diffs and power dividers maybe you need to reevaluate the way you drive.

 

I thought magoo was pointing out I made an incorrect statement that 12 was direct and that would be tenth. I thank he also made an incorrect statement because most 13's were single overs. Shame on me and the hell away with that.
The conversation made me question myself and I went searching. Under Eaton Transmission Ratios found all factory made transmissions listed with their ratio in each gear. There were 3- 00's (double overdrives) in the 95, 11, and 14 series. 13th was .62 OD, 12th was .73 OD, and 11th was .84 or .85 OD. The RTLO13's and 18's are .73, .86, and .1.0. in the top three gears, as I read it.
Those shift decals can be confusing to me also but I cannot name model numbers and how the the shift pattern is labeled. I will just say in RTLO 14 series 15 you cannot shift 15 gears in progression and the 7 speed you can shift more.
Now for making this a fuel economy thread I was in one of those. I do not remember the poster that stated years of records and 62 MPH is the place to be. I was and still am learning on line edicate and am sure I made him mad. In his application I am sure he is correct. I was refering more to running rolling hills and I feel that if I had an ECM engine with the same HP setting on the pedal as on cruise I could bump anyone letting the cruise be the operator at least a mile per gallon. The truck might go 78 or 48 but it would never make a hard down shift to max RPM 200 feet before the crest of the hill.
You can speed a lot of money in the school of hard knocks and I will share some with you. Glad this was not my money so I learned for free. Strong 400, direct 9 speed, 11R 24.5's, 3:70's? Put in a RTO 1110 0.79 OD and he liked that. Decided more is better and bought a RTOF 12609 B with 0.73 OD. Hatted it because had to shift gears all day and mileage went down. That is only a 6% difference. Went back to a lower OD ratio later.

 

Besides speed or fuel economy, one of the early reasons for having a double over was to let you have a slow speed ( higher ratio ) rear end for startability, and the end of the national 55 mph speed limit.
Direct drive trucks early on were pretty slow, 50 - 55 mph. With the elimination of the national speed limit, if you put in a fast speed ( lower ratio ) rear end and you were loaded heavy sitting on a steep hill, startability suffered.
With a double over drive you can have the best of both worlds.

 

I got the best mpg with 12.7 Detroit 430/470, 10 speed direct, 2.79 axle, 22.5 low profile rubber, Freightliner Century condo.

 

C15 cat
550 hp
4:56 rear ends
18 speed duel over
I pull 140,000 lbs, through the mountains, never need to shift into low range.

 

With those rear ends from God, I don't think you ever need low range on any hill. lol.

140K is righteous when done right. A tip of hat to you sir. Ive been around that heavy a time or two before with really crappy transmissions and engines.