Gear Ratio Choice
Thread Starter
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Junior User
Joined: Feb 2005
Posts: 66
Likes: 2
From: Surrey, BC
Gear Ratio Choice
Just found that I need a new rear gear set. Went to change the rear seal and noticed that half the gear is heavily rusted, like the truck sat for a long while. That explains the howl at highway speeds. The truck is a 1965 F100 short box with a 300 I-6 and a C6 Tranny. The current rear gear is 3.7 (or so) and the rear tires are 255/70R15 (~29.1 inch diam according to BFG catalogue). I drive mostly on the highway to work everyday at about 70 - 75 mph, so I would like a highway gear in it. If my calcs are right switching from a 3.73 gear to a 3.23 would bring the rpm at 75 mph from 3230 down to 2797. Any opinions on the new ratio, is it too low, too high. What are other's running?
Posting Guru
Joined: Jul 2003
Posts: 2,232
Likes: 1
From: Colville, Washington
I think the 3.25:1 would be good for your use, as long as you don't expect to tow or haul alot. It would still work, just not as well as your present ratio. The 300 makes good low end torque and the automatic gives you some torque advantage getting started.
Freshman User
Joined: Aug 2003
Posts: 39
Likes: 0
From: Scherz, TX
think passing power on the highway though. My 97 had 3.55's and I put in 4.10's to make it faster, but when we bought our '05 we first looked at and STX with 3.08's and I almost got in a wreck on the highway test drving it because some idiot was maintaining speed with me while we was trying to get off the side of the highway. I couldn't speed up since the gears were so weak so I had to slowdown to like 50mph on a 70mph highway so he could get on. You might save gas mileage but I would rather have safety living here in Texas and low gears smaller gears won't get the job done.
Thread Starter
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Junior User
Joined: Feb 2005
Posts: 66
Likes: 2
From: Surrey, BC
Ended up putting in 3.25 gears. Highway speeds are nice especially getting into the fast lane the truck doesn't seem like it's going to break apart. If my calcs are right, then with the new gears at 60 mph I'm at 2250 rpm, which I think is reasonable.
