To anyone wondering about the history behind these “baby Road-Ranger” transmissions with the shifter mounted air button operated cointershaft brake, I’ll share what I know about these interesting units. These were the “baby 10/13 speeds”, models RT(O) 610, 613, 6610 and 6613. They all use the same housing and the same parts in the 5 speed “front section”. The difference in the “66” series and the regular “6” is the 66’s use bevel cut gears in the timed, air shifted “back / range box” for quieter, smoother operation over the straight cut gears in the 610 and 613. The “13” speed models in this series were extremely unique as they were actually a 15 speed in design because they used the 610/6610 10 speed box with a deep reduction auxiliary section on the back…..but unlike all the other “15 speeds” these were actually named accurately. All 15 speeds are built on the same formula (10 speed main box with deep reduction added) but they don’t actually offer 15 non-repeating forward gears. Shifting sequentially a 15 speed only has 13 unique forward ratios you can use, the last 2 deep reduction gears are actually slower than the lowest two “regular” gears. The shift pattern for the 613/6613 is actually the pattern you use in all the 15 speeds to get from the lowest gear to high without shifting down again. Of course all the other “13 speeds”also offer 13 unique forward gears as well but they do it a different way, giving 5 gears in low range and 8 in high by using a a “splitter” type auxiliary section in the high range gears…..All the other 13’s (along with and 8LL and 18 speed) are built on the 9 speed main box, but they didn’t make a 9 speed as small as the 6/66 series making the baby 10 and 13 “one-off” models with no replacement after they stopped production. They are (conservatively) rated for 600 ft-lbs of input torque and were actually pretty common in medium duty trucks with air brakes from the late 60’s up to the 80’s…..they basically replaced the “twin stick” 4/5 x 3/4 transmissions common in the higher GVW “medium duty” model trucks at the time and were a common retrofit to these trucks as well. The most common application I’ve seen them in is Ford L700(0)/800(0)’s with the 534 Gas, 3208 or 8.2 Detroit but they were popular in similarly sized and powered IH and GM trucks as well.
Besides the Diesel engine of course the road ranger transmission is the single greatest invention to come to the trucking industry in my opinion. Easy to service very strong many different options to suit whatever the need may be. Engineering at its finest
I was working as a machinist thru highschool. We had some old gas burner trucks with 2 speed rears. At the time I knew where I could have gotten a couple Road Rangers. Everyone said they would suck up too much power from from our old trucks turning all that gear mass. I knew machining the adapters wouldn't be any trouble, but didn't wanna do the work , if it would use up too much of the power of our old 292 inline sixes , or the 350 small blocks. I know a stock 12 valve has enough zap for about any person for everyday abuse. Have y'all noticed any draw from the power it was putting through the slushamatic??? I'm retired now , and still have an old 65 C60 Chevrolet the little 292 has plenty of power , if you keep it in it's happy place or RPMs. A 10 - 13 - 18 speed would be so much easier and faster between shifts than the Old 2 speed rear end. I kept this truck , because it pulls as well as any of the small block V8s , plus it only sips gas compared to even the 283 , or 327 V8s. I wanna make this old girl into a camper puller. I just don't wanna do the work , and expenses if it'll kill the power. But this is a subject that I've pondered for well over 40 years
I had a 75 ford f250 with a Perkins 6 cyc and a RT610. I loved that truck, nice thing about the road ranger trans is it only has 400 rpm drop between gears. Mine had a 16 in clutch, and a flywheel from a c60 truck.
I would not feel safe towing more than than the recommended weight in a first gen Ram. I have one. They are not confidence inspiring vehicles lol. Plus, if you get into an accident towing more than the OEM specs, you are going to prison.
Hats off to you! You can pull as much as you are comfortable with, without killing the engine. I have wanted to do this to my 2009 Chevy dually with a tired 6.0 gas and a 6l80e auto… Cummins and a 10 speed swap
Used to herd tandems with 3208's and 466's and all had 13-unders with the countershaft brake. Used just for getting it in gear or either scrubbing for a week while waiting or just shut the diesel off and yank it. A 13-under has it all. Moved a 20 ton track loader on a 20 ton rated tilt top trailer and never missed a lick here in the hills. Always wanted a G.I. 5-ton with a 10-speed. Herded a Pete tri-axle with a 3406 and empty went from lo-3rd, lo-5th, hi-3rd, hi-5th. Never did know what a load was. Blessings!
Man this truck brings back such memories! I grew up on the farm and my Grandpa had an all red non dually 12 valve.... and had the same color interior...It was an automatic though... That truck took a beating! I mean it worked HARD its whole life.... Well the engine out ran the body... The body and frame were so rotted out from rust .. It was a Michigan truck.. But the day she left she RAN like a dream! Had them adjustable bands in the transmission .
Great review! Medium duty transmissions, Fuller FSO, RTO and Allisons are mentioned here. FSO-6406 have input torque rating 660 FtIbs and FSO-6806 rated input 860 FtIbs, Both FSO weight 359 pounds, OD 0.78, and both are 6 speed and good for max GVCW of 33 tons (approx 70,000 pounds).......... I am pretty sure the smaller light weight 2 counter shaft 10 speeds (RTO610 and 6610) are both medium duty rated transmission and not heavy duty rated, most likely same GVCW as FSO's........The RTO-610 (is the older one) great 10 speed, input torque is 600 FtIbs, OD is 0.8, weighs 425 pounds, good for max GVCW???? (I could not find it) Replacement newer RTO-6610 input torque 660 FtIbs, rest should be the same as RTO-610, again I could not find GVCW but both are light weight 10 speed so should be close to FSO ratings........ As for automatics, the Allison 3000 series is excellent, much better rating than the Allison 1000/2000's, it also has double OD (0.75 and 0.65) and good for approx 40 tons (80,000 pounds) GVCW. It will take approx 425HP, and input torque approx 1200 FtIbs..........In reality does not matter which transmission you use, the weakest link will always be the chassis and drive line (drive shaft, u joints), and rear axle in our pickups. I have 2 older pickups, both Cummin's, one is 91 Dodge D350 with FSO-6406 and another 95 3500HD GMC with Allison 3000. Love them both and will never sell either one........ BTW Allison 1000/2000 are great too, nice and small but a much lighter duty trans than any of the above. Depending on the model, max GVCW is 25,000 to 32,000, and input torque and HP is much lower of course (max approx 300-325HP, 600-660 FtIb). All of these transmissions will make any pickup truck that much more reliable for work!
