rear axle swaps
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Elder User
Joined: Feb 2015
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From: south east kansas
rear axle swaps
supposedly most f100's have a 28 spline 9" in them and most f150's have the 31 spline 9" will I have a 1973 f100 with axle code 02J, and I have a 77 f150 31 spline 9" could I just swap the axle no problems, and how would I tell the gear ratio of the 77 9" without the vin?
Posting Guru
Joined: Aug 2010
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From: Knoxville, TN
Not sure on which spline counts came in which vehicles, but to determine your current gear ratio, jack the truck up, put it in N, and count the number of revolutions of the driveshaft per revolution of a tire. (To get finer resolution, go for more revolutions, i.e. driveshaft revs per 10 turns of the tire, etc.)
Lead Driver
Joined: Apr 2011
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From: El Dorado, Arkansas
If no one has changed anything, a '73 F100 with an 02 rear end ratio code would have a 3.00:1 ring & pinion with a single track differential.
MOST '72 and earlier F100s had 28-spline axles. MOST '73-'79 F100s and '75-'79 F150s had 31-spline axles.
If the 3rd member is out of the rear end housing, you can count the number of ring gear teeth and the number of pinion gear teeth. Divide the number of ring gear teeth by the number of pinion gear teeth and you'll have the exact rear end ratio.
MOST '72 and earlier F100s had 28-spline axles. MOST '73-'79 F100s and '75-'79 F150s had 31-spline axles.
If the 3rd member is out of the rear end housing, you can count the number of ring gear teeth and the number of pinion gear teeth. Divide the number of ring gear teeth by the number of pinion gear teeth and you'll have the exact rear end ratio.
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Elder User
Joined: Feb 2015
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From: south east kansas
2 quick questions, where on the ring gear are we talking, and my truck is a 73 model but was built in October '72 so could it have the 28 spline?
if I cant find it i'll start counting
if I cant find it i'll start counting
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