Gear swaps
Thread Starter
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Posting Guru
Joined: May 2004
Posts: 2,161
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From: Prince George, B.C.
Gear swaps
Hey all, this isn't totally truck related but....
I am building a '79 Town Coupe for a Hit-to-Pass race and need to know if the rear diff is the same as a 9" as far as swapping gears, the way it is setup now it will do about 60mph in 1st gear and the poor little 400 just can't pull it. I need to know if I can swap the gears from a 9" pickup diff into it or not.
I am building a '79 Town Coupe for a Hit-to-Pass race and need to know if the rear diff is the same as a 9" as far as swapping gears, the way it is setup now it will do about 60mph in 1st gear and the poor little 400 just can't pull it. I need to know if I can swap the gears from a 9" pickup diff into it or not.
Cargo Master
Joined: Dec 2003
Posts: 2,735
Likes: 38
From: Sunny Florida
The car will have 28 splines and the truck should have 31 splines. There are few early trucks and F100's that may have 28 spline gears in them but for the most part all trucks are 31.
You can how ever swap out the spider gears and convert the 31 to a 28 spline set up.
You can how ever swap out the spider gears and convert the 31 to a 28 spline set up.
Thread Starter
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Posting Guru
Joined: May 2004
Posts: 2,161
Likes: 1
From: Prince George, B.C.
Ok, What would be a good guess as to what thes car and my 2 truck diff would be for gears? The diffs are from a '78 F100 300 6, C6 and the other is from an '81 F-100 300 6, 3 on the tree. I'm trying to get all this worked out but I guess it can't hurt to start pulling diffs apart and checking if I can convert them to use the car axles.
Cargo Master
Joined: Dec 2003
Posts: 2,735
Likes: 38
From: Sunny Florida
The gear ratio could be anything. The truck could have been ordered with any gear ratio one wanted. I have found 3.00, 3.25, 3.50 and once I found a 3.70 behind a 300 6cly. motor. Not all of the trucks were F00's. For the most part they were F150's. If I had to guess I would say you have a 2.75 gear and that appears to be the most common ratio out there. I would also say they have 31 spline axles. but I could be wrong so go tear them down and see what you have.
