rear gear selection
Thread Starter
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Tuned
Joined: Oct 2011
Posts: 312
Likes: 12
From: Warsaw
rear gear selection
The 223 I6 in my '62 F100 winds a bit tighter than I would like at highway speed. The VIN tag and toe tag on the diff both show a 3.70 ratio. I'm thinking about a 3.25 or 3.00:1 ratio and would like to draw from the experience of other forum members. The engine is stock except for headers, a 38/38 Weber carb on a Clifford manifold and a later model distributor. The truck is a daily driver and will likely never see north of 70 MPH.
Mountain Pass
Joined: Oct 2018
Posts: 111
Likes: 0
I had a different motor, but I swapped my rear gears from 3.89 down numerically to a 3.25 and I’ve been very happy with it. I don’t have a tachometer so I’m not sure how fast it’s spinning. I typically run around 67mph on the highway and my 292 y block seems pretty happy at that range.
Cargo Master
Joined: Jul 2015
Posts: 2,063
Likes: 137
From: tucson
My '66 with a 240 had 3.50:1. I swapped in a 3.0:1 after some teeth broke on the pinion gear. I like the 3.0 but starting on any good slope is an effort for the old engine. I'm thinking that the 300
I'm going to put in will work well with the 3.0 gears. Unless you already have the gears, I think 3.25 would be the make you would want with the 223.
I'm going to put in will work well with the 3.0 gears. Unless you already have the gears, I think 3.25 would be the make you would want with the 223.
Tuned
Joined: Oct 2018
Posts: 368
Likes: 6
My '66 with a 240/3 speed also had/has a 3:50. Probably the perfect gear for the use, as I can get up hills (I live in Wisconsin), and still cruise at 85 if need be. As has been stated, going much taller will overly stress takeoff, leading to early replacement of the clutch.
Thread Starter
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Tuned
Joined: Oct 2011
Posts: 312
Likes: 12
From: Warsaw
Thanks to everyone for sharing your personal experience. Using Spicer's rpm vs mph calculator I came up with 2639 rpm @ 65 mph using 3.25 gears which is livable. Having one built using all new parts.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
The 223 I6 in my '62 F100 winds a bit tighter than I would like at highway speed. The VIN tag and toe tag on the diff both show a 3.70 ratio. I'm thinking about a 3.25 or 3.00:1 ratio and would like to draw from the experience of other forum members. The engine is stock except for headers, a 38/38 Weber carb on a Clifford manifold and a later model distributor. The truck is a daily driver and will likely never see north of 70 MPH.
John
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Lead Driver
Joined: Jun 2006
Posts: 5,653
Likes: 978
From: Near Yosemite CA
I'll throw in my .02 fwiw... my 66 F100/240/T18 had 3.00's in it when I got it (I didn't know the ratio), was just a bit of a dog up here in the mtns, the flats were..ok..thought the 240 was just tired, came across a 302, figured I throw in while I rebuilt the 240, in the meantime, rear end started making noise, pulled it, found out they were 3.00's, swapped with a guy for a 3.70 9", Holy cow!! Huge difference, brought Shrek alive, I then changed to 15x8 rims with 265/70/15's, speedo is spot on and I get 18mpg running to fresburg and back now.
All this just to say, don't go too high a ratio, you'll be out of the intended rpm range and you won't like it, buy a Tach also.
All this just to say, don't go too high a ratio, you'll be out of the intended rpm range and you won't like it, buy a Tach also.
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Mountain Pass
Joined: Apr 2020
Posts: 105
Likes: 10
Dave, who do you have doing the work? I have a leaking pinion seal and I'm having a heck of a time finding a shop to do the work (I'm considering gears and wheel bearings while its apart). The most recommended shop here in Norfolk is closed due to our friend COVID-19.
Thread Starter
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Tuned
Joined: Oct 2011
Posts: 312
Likes: 12
From: Warsaw
Dave, who do you have doing the work? I have a leaking pinion seal and I'm having a heck of a time finding a shop to do the work (I'm considering gears and wheel bearings while its apart). The most recommended shop here in Norfolk is closed due to our friend COVID-19.
Thread Starter
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Tuned
Joined: Oct 2011
Posts: 312
Likes: 12
From: Warsaw
Mr Dave, when your truck was designed, it was only meant to go about 45 mph, they were mostly driven on dirt roads and trails so higher ratios were installed. A lot has changed in the nearly 60 years since it was built. I wouldn't recommend going below 3.25 because you will kill the pulling power. my 2
John
John
Mountain Pass
Joined: Apr 2020
Posts: 105
Likes: 10
Thread Starter
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Tuned
Joined: Oct 2011
Posts: 312
Likes: 12
From: Warsaw
I'd like to thank everyone for their input. The 3.25's are in and worked out quite well. RPM dropped to the comfortable level and the engine has no problem pulling the hills here in the Ozarks in high gear.
