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My '75 KW W900 has a 290 cummins with a 9 speed trans. I think it has 4:10 gears cause the top end is about 60mph at 2000rpm. Could this low top end speed have anything to do with the way the engine is governed or just the gear ratio?
 

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Albertabuck would be the guy to ask for advice . Other than changing the diffs to a higher ratio adding an auxiliary transmission would be your other option .
 

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I have a 1964 White Freightliner with a 220 in it and you have to run it at 2000 rpm to get any power out of those old engines.
 

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Is it a direct drive or overdrive 9-speed? Also, what tire size?

I have a '90 Peterbilt with a 350hp B-model Cat, 9 overdrive, 4.33 gears and tall 24.5 tires. At 60 mph it's turning just over 1500 and will do almost 80 at 2000.

From your description I would guess you either have a direct transmission and tall tires or short tires to go along with your short gears. My old Pete will do about 55-60 at 2000 in 7th (direct drive) gear.

Mark
 

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See if you can find a tag on the transmission and jot down all the info off of it into this thread as I think that will give a good indication as to it being a direct or overdrive unit. As to the diffs, if no tag or information on them you could simply rotate the wheels one revolution after marking a tire ( arrow pointing down to the ground for example ) and a mark on the drive shaft flange and corresponding on the diff housing. I've done the rolling truck method too with someone behind the wheel and of course staying out of the way of the tires and just observing the driveshaft and in that case it was a 4.10 so the shaft turned just over 4 turns with the tire making that one revolution, quick and easy to know what gears are inside a diff that way.
 
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