rearend swap
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From: Dora Alabama
rearend swap
my 1976 F-100 has a 302 C6 and 3.95 gears in the rearend. It will run about 70 mph. I have another rearend that has 3.03 gears. If I swapped them out about what would my top speed be
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About the same. You will just be spinning the engine at a lower rpm.
If all we had to do to reach a higher speed was change gears, we could all run 2.5:1 rear ratios and go several hundred miles an hour. Unfortunately it does not work that way. Torque gets us motivated and horsepower keeps us motivated. Gears just determine the rate in which we get there, and the rpm we have once we are there.
If all we had to do to reach a higher speed was change gears, we could all run 2.5:1 rear ratios and go several hundred miles an hour. Unfortunately it does not work that way. Torque gets us motivated and horsepower keeps us motivated. Gears just determine the rate in which we get there, and the rpm we have once we are there.
Ford Parts Specialist
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From: Simi Valley, CA
Originally Posted by J Hodges
my 1976 F-100 has a 302 C6 and 3.95 gears in the rearend. It will run about 70 mph. I have another rearend that has 3.03 gears. If I swapped them out about what would my top speed be
You have a Ford 9 inch rear axle. There are no such gear ratios as 3.03-1 or 3.95-1 available or ever offered. The gear ratios available for 1973/79 F100/150's were: 2.75 / 3.00 / 3.25 / 3.50 / 3.70 / 4.11. As original, the rear axle ratio on a 1976 F100 302 would prolly be 3.25-1. Look on the VIN plate for the 3 digit AXLE code...it can be translated here on FTE or post it. This code will tell you what axle ratio came with the truck originally.
Ford Parts Specialist
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From: Simi Valley, CA
Originally Posted by J Hodges
Actually my truck came with a 360 or 390. The 302 C6 was swapped in. I didn't know all of these trucks really had a 9 inch rear
Rarely seen on a truck of this vintage is the Dana 44, which has a removeable cover on the back,
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bigger tires also work just as well as a lower ratio.. but if you top out at 70, it sounds like it's a lack of power more than it's gearing. If you were pushing 5k RPMs at 70mph I'd say to swap the diffs or get bigger tires but I highly doubt you are.
only the people without OD AND running a strong engine and/or really tall gears will max out the drivetrain before they max out the engine in trucks like these.. and even then, they'll probably already be going faster than they should.
http://www.speedworldmotorplex.com/calc.htm - if you were running 31'' tires you would max out at about 120mph with 3.95:1 ratio..
edit: If I'm not mistaken, these trucks run 28'' tires stock, so you would top out at about 105 with your current gearing.
only the people without OD AND running a strong engine and/or really tall gears will max out the drivetrain before they max out the engine in trucks like these.. and even then, they'll probably already be going faster than they should.
http://www.speedworldmotorplex.com/calc.htm - if you were running 31'' tires you would max out at about 120mph with 3.95:1 ratio..
edit: If I'm not mistaken, these trucks run 28'' tires stock, so you would top out at about 105 with your current gearing.
Last edited by ErrorS; Jul 14, 2007 at 03:20 AM.
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
Originally Posted by ErrorS
bigger tires also work just as well as a lower ratio.. but if you top out at 70, it sounds like it's a lack of power more than it's gearing. If you were pushing 5k RPMs at 70mph I'd say to swap the diffs or get bigger tires but I highly doubt you are.
http://www.speedworldmotorplex.com/calc.htm - if you were running 31'' tires you would max out at about 120mph with 3.95:1 ratio..
edit: If I'm not mistaken, these trucks run 28'' tires stock, so you would top out at about 105 with your current gearing.
http://www.speedworldmotorplex.com/calc.htm - if you were running 31'' tires you would max out at about 120mph with 3.95:1 ratio..
edit: If I'm not mistaken, these trucks run 28'' tires stock, so you would top out at about 105 with your current gearing.
Not according to the axle ratios offered. There's no such 9" axle ratio as 3.95-1. None = Ford never offered this ratio = ever.
The closest ratio is 3.89-1 and that ratio was used on cars from 1957 thru 1964, and trucks 1957 thru 1966.
Last edited by NumberDummy; Jul 14, 2007 at 03:37 AM.
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Posting Guru
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All besides the point, even if he had a 5:1 ratio he'd top out at 85MPH. So regardless of what he has, gearing will not help.
Maybe it's a custom job or something.. wouldn't be the first time
Maybe it's a custom job or something.. wouldn't be the first time
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From: Dora Alabama
I was looking at the wrong codes. I was wondering why a truck with a 360 would be geared lower than a truck with a 300. Since both of these rearends are 9 inch are they the kind that hotrodders use.
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