Like trucks and engines, transmissions have changed with the industry. Today you can get an autoshift 18 speed when 30 years ago the only way you could get 18 speeds was with a 2 stick transmission. Lets look at a few changes and specific transmissions from years ago.


O and X, they're not just for hugs and kisses

Overdrive transmissions had "O's" in the name, such as RTO-14610 whereas the direct drive version of the same transmission would have just "RT". But there were also different shift patterns. Direct transmissions had the pattern we're typically familiar with, the 2nd to last gear being in the upper right hole and final gear being in the hole below. But overdrive transmissions were offered with the last two gears positions reversed.
For example, an overdrive RTO-14610 transmission manual would have 9th gear in the lower right hole and 10th gear in the upper right hole whereas the direct RT-14610 transmission would have those gears in their regular positions.

So what about the "X"? The X denotes an overdrive transmission with a direct drive shift pattern. An RTX-14610 transmission would be overdrive but have the last 2 gears in the same position as the RT-14610. The "O" shift patterns have since been discontinued in order to harmonize things. Newbie drivers going from an "X" to an "O" pattern might find themselves tearing up transmissions, lol!

It's important to note that the traditional 13 speed transmissions from Eaton starting with RTO do not have the reversed top gear positions since they are actually based on eaton's direct 9 speed transmission with an added 17% overdrive splitter gear in the auxilliary section.


The RT/RTO-6613: the 13 speed with 15 gears.

The 6613 transmission differed from the traditional 13 speed transmission. Unlike the usual 13 speed transmission that was based on a 9 speed main box with a splitter gear, the 6613 used a 10 speed main box with a high/low/double reduction low auxilliary box. Now this might sound familiar since it's similar to how a typical 15 speed transmission is constructed. While it offered 15 ratios, there were overlapping ratios so there were only 13 successive ratios available, they were typically selected one of two ways:

DR1-DR2-DR3(shift to low)1-2-3-4-5 (range shift) 6-7-8-9-10

or

DR1-DR2-DR3-DR4-DR5(shift to low)3-4-5(range shift) 6-7-8-9-10

The 6613 also offered 3 reverse ratios.

It's interesting that Eaton called it a "13 speed" despite it offering 15 separate ratios when on it's 15 speed transmission, which as I metioned before is constructed similarly to the 6613, only 12 successive ratios are available (due to the same overlapping of ratios).

The 6613 was discontinued sometime in the early 80's, though used units are often sought after by medium duty truck owners.

Unlike the traditional 13 speed transmission, the RTO-6613 had the top two gear positions reversed.


The 3 position Eaton 13 speed shifter

Eaton used to offer a 3 position splitter button for both it's traditional 13 speed transmission and the 6613. It had "Low, Direct and Overdrive". The "low" splitter position took place of the high/low range button. Switching the splitter from "Low" to "Direct" or "Overdrive" would change the range from low to high.

On the 3 position 6613 shift button, the 3 positions were "Low, Int, and Dir (or Over)". The "low" position put the transmission in double reduction and the "Int and Dir/Over)" switched between the low/high ranges.


The "underdrive" 13 speed.

Eaton used to offer a 13 speed transmission with a direct drive 13th gear instead of the traditional overdrive for customers who wanted the flexibility of a 13 speed transmission but the fuel savings of direct drive. It was based on the 9 speed direct transmission with a 17% underdrive splitter gear in the auxilliary drive section.


The "triple overdrive" 13 speed.

This transmission was based on an Eaton 9 speed overdrive transmission with a 17% overdrive splitter gear added to the auxilliary section. This provided 3 overdrive gear ratios as well as direct with the last 4 gears.

7 Dir: 1.00 (10th)
7 Over: .85 (11th)
8 Dir: .73 (12th)
8 Over: .62 (13th)

With a .62 overdrive, trucks with this transmission had pretty long legs.

Eaton referred to this transmission as "double overdrive". The name started with RTOO. Since it was based on the 9 speed overdrive, the 7 and 8 gear positions were reversed. Eaton offered a double over drive version of this transmission with a direct shift pattern, with the name RTOX.

The RTOO transmissions were dropped in the mid 80's.

The current generation of 13 speed (and 18 speed) transmissions have two overdrive gears, .86 and .73 but Eaton doesn't consider them "double overdrive". The .86 gear is generated by a 17% underdrive splitter gear.


Spicer's "no repeat" multi speed transmissions.

Spicer was well known for it's twin stick transmissions. In order to simplify matters, Spicer combined the two shifters into one. The main pattern was non-repeating (no range shift) with a shift knob that had a splitter button with up to 4 positions. The use of those positions depended on the transmission. Spicer offered a 14, 16 and 18 speed transmission using this system. Each of those transmissions also offered 4 reverse ratios.

Spicer stopped offering these transmissions in the US some time ago but a company that builds spicer transmissions for the Latin American market under license still offers them in Mexico.

Mack also offered similar transmissions.

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Good info interesting !!!!!!!

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RoadRocket

Yes I'm totally unimpressed. You did'nt cover Mack 5 x3 and 5 x 4 Spicer w/cable linkage and I drove a 13 spd with a 4 speed overdrive cablelinkage trannie and a 2 speed reducer. Under the hood was a 12 cylinder Caterpillar and we used it in the oilfield. It came from Canada was a KW with steel fenders and you could get out and walk around it while idling in the lowest gear. I'm a 2 stick man, u got a problem, I got a plan.

I'm just needling you PACKRAT. I love it when a Mexican uses the Jake Brake and shifts that old Spicer. It has to be hard on the whole drive train form the crank to the rears.

You can still get the spicer boxes from an American company. They build crane chassis and drill rigs. I can't recall the name of them right now but I got parts for a 4 speed aux from them about 5 years ago. I think I still have the catalogs they sent me someplace. I no longer have the truck. It was a KW 900-A with a 5x4 and it was fun to drive. I had it about 8 years running that setup. I still sometimes grab for the shifter for the back box when I'm climbing a hill. I have a 13 speed now in one truck and a 15 in the other.

i rember driving with a 7-speed spicer no hi -low side in transmission you start shifting gears and work your way toward th passenger door