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Gearing help

709 Views 4 Replies 3 Participants Last post by  TravisT
I have a 1997 F-350 ps, DRW, 5-speed, and what I believe to be a 4:10 gear ratio. I tow from 10,000 to 12,000 pounds frequently and really like the low end gears I have. However, upon reaching highway speeds, my tach is showing approx. 2400 rpm. I can also watch my fuel gauge moving to the left. I have considered changing my gear ratio to 3.73 to help with the fuel usage but I'm worried about my ability to get moving in 1st gear. Any ideas on how a change to 3.73 gears would effect my low gears?

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Wow - Welcome to the site!!! 1st post! Glad your here.

The only advice I can give you is based on my own experience. Here is what I found:
3.55s with stock tires was OK - 19.5mpg - no tow. Then went to 35" tires and the truck bogged down dramatically BUT first gear was still too LOW to start off in unless I was poited up hill.

The good thing was that the RPMs were down on the highway and it was nothing to run 80-85 continuously. BUT the fuel economy suffered because of the increased drag.

Then the rear end chewed itself up and I went to 4.10s. Now the RPMs are up and the mileage is up but just a tad. Now I can't drive 85 because of the RPMs. Also the EGTs are MUCH lower.

Now I don't tow like you do so I'm not in that game, but I'd say that if you were to do a change, go with the 3.73s like you said and not 3.55s. Your EGTs will be up, and your mileage will likely drop some. And first gear will be just fine with 3.73s.

Hopefully you can piece that info together and make judgement.
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Yes that's what I meant. Empty weight my EGTs were around 900* at 75mph. Now with the 4.10s the EGTs are at 750* at 75mph. That's a significant difference. And it takes extra fuel to make all that extra heat.
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