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F-650 transmission question


California Chapter member
First off I can't seem to upload pics of the new truck for some reason but that is not the question.

The tranny is an Allison RDS 2500 which I believe is a six speed but it goes like this[left to right] R N D 4 2 1 I believe drive is overdrive despite it not having the over on the D but Im wondering how do I get to 5th and 3rd or I'm I supposed to haul and tow in overdrive? In the C4500 I would haul and tow with the overdrive off and I would slow down using all of the gears and I'm nervous of going to 6 to 4 and even more from 4 to 2 with such high speed and weight.:suspicious:
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The Token Canadian
Staff member
If it is anything like the 3000 series, 4th is direct and 5th/6th are OD.
Everything is an engineered package, put in in D and you are good to go.

When the OEM specs a truck, Allison runs a simulation to ensure that all will be running within spec...I know this as when I got my 750 and had a 4WD conversion done, there was an issue with available gear ratios for the front axle.

The one I chose was just slightly below what Allison recommended and the result of that was occasional turbo stall...which was dealt with by manually shifting...I could have had the transmission reprogrammed but since I was the sole operator I said screw it.

If the transmission has a "mode" toggle, my suggestion would be to leave it in the standard setting, the "econo" one results in less performance and negligible fuel mileage increase.

My truck ran between 27-30K pounds with the added drag of that front drive axle and the transmission was perfect.

Also....transmission will not shift if rpm's are out of acceptable range
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that trans should be fully electronic so if you were to pull the cable from D to 1st if will down shift its self if i remember right. based on the shifter i think your talking about, they put 1 and 2 for crawl presets for say 10mph speed on dirt roads, so the trans wont hunt gears, 4 for preset direct maybe getting a bit more revs on steep hill that keeps wanting to shift you out of the needed power band. truth be told aside consent slow speeds you shouldn't have to move the gear selector out of drive. that trans if rated to run in 6th at 33,000 gvw


don't play well w others
Like said above, the computer does the shifting , the only thing you need the lower gears for is to keep it FROM shifting

One thing to keep in mind, DO NOT use the Jake brake unless it is in D, you will blow the head bolts loose