I have a 94 Freightliner FLB cabover with a RT series 9 speed. No over drive means 9th gear ratio is 1:1 my axle ratio is 3.36:1
At speed of 70mph the engine rpm calculated to just over 2000 rpm with new 22.5 tires.
What would be the easiest and cheapest way to get an over drive? Thinking of switching to a 10 speed. Most are .74 ratio in 10th which would lower my rpm at 70 down to 1500 roughly.
Also a 9 speed with OD would do the same.
Unfortunately my transmission model is not a convertible 9 speed so i cant just have it converted to a 13.
What are your thoughts? I will be hauling 80k lbs everyday with minimal hills. Hauling ethanol from KS to OK. Only hills are in southern OK in the Arbucle mountains. But its just 1 massive hill then flat land
9 Speed to a 10 speed
Discussion in 'Trucks [ Eighteen Wheelers ]' started by Oakcityarms, Aug 17, 2019.
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I don't mean to be a smart ### here. But it might be a lot cheaper to just slow down.
BoxCarKidd and haycarter Thank this. -
Really doesn't matter what transmission you pick so long as it is an OD model. That is if your end game is to lower your top speed RPM. A 13 doesn't automatically mean OD either as in some cases the OD ratio comes from the main box, not the aux section.
BoxCarKidd and Oakcityarms Thank this. -
Check the lengths. I think 9's are the same length as a 13/18, and wouldn't require redoing the driveshafts. The manuals are all available on the Eaton website
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What model is your 9 speed?
The least expensive way is to find a good gear head. Push the front two gears off the counter shafts and swap them. Also swap the drive gear and the front gear on the main shaft. That probably gives you about 18% OD. Put in a bearing kit and replace any worn parts while there.
I thank that 11.1 Detroit likes a little RPM and won't lug down well like a big Cat. If you get over geared you will find yourself down shifting on every little grade and wishing you were still just humming along in 9th.
13 and 18 spds are more versital.KVB, FinkPloyd, spsauerland and 1 other person Thank this. -
Im thinking a RTO12609A or a FRO16210C or RTO14210 or similar. -
You can find all of the Eaton Fuller Transmission Ratios and models on line. Search that and or things close to that. When you have the one I like it lists every model ever made and every ratio in every gear. Also has the length. There are different length yokes also.
Some models have high speed reverses and low gears. Jumping up over a 14 series will have a lot of unexpected problems.
I did not see a RT12906A right off but if you do as I mentioned you will have RTO12906A.
You can also go to Eaton road speed calculator and fill in the blanks. They will give your road speed possibilities. Have fun and I hope you make good choices. -
What about swapping the rears out to say, 2.64? Just a thought.
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Well im apparently dyslexic its a RT12609A. and i have been consulting the ratio guide they have.
BoxCarKidd Thanks this. -
That 9 over transmission was a good match with 3.55's, NTC 400 and 22.5 tires.
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