Making a 9speed OD

Agtech1206 · Aug 12, 2016

BoxCarKidd said: ↑

062 is on tract. If you put a 13 spd box on the back of that will give you about 12% overdrive. If you swap the gears in the front of the main box that will give you about 18% OD. Do both for about 30% OD.
There are many different options, transmission models, and ratios which maybe indicated by only a letter like B. RT12609B = 22% OD.
This is all off the top of my head and only meant as an example. The point of my reply is to inform you of this and that if you over gear for your HP and torque you will be shifting all the time. That will defeat your fuel savings and wear you out.
There is a Eaton sight on line that will answer all of those ratio and road speed questions.
The 13 speeds worked really well on lower HP engines because you could shift about every 450 rpm and keep them in their best rpm range.
What engine do you have?
Click to expand...

I have a 1979 transtar II. With a big cam Cummins around the 400HP range and currently a RTF 11609 trans and single axle 433 ratio. I'm just going to be pulling a trailer with tractors on it and hualing grain in the fall most weight I will hual is 40k. Plus trailer weight. I'd like to be able to go 70-75 mph right now I'm against the governor at 2200 at 58-60 mph

Agtech1206 · Aug 12, 2016

Agtech1206 said: ↑

I have a 1979 transtar II. With a big cam Cummins around the 400HP range and currently a RTF 11609 trans and single axle 433 ratio. I'm just going to be pulling a trailer with tractors on it and hualing grain in the fall most weight I will hual is 40k. Plus trailer weight. I'd like to be able to go 70-75 mph right now I'm against the governor at 2200 at 58-60 mph
Click to expand...

JPenn · Aug 12, 2016

That's a nice little truck. I'd love one of those to yank doubles with.

BoxCarKidd · Aug 13, 2016

RTO11609A looks like .74% OD on Eaton sight. That should give you the road speed you want at a little less RPM. Your engine has enough guts to pull it. Day job for a good trans man.

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