Rear axle ratios in 57-72 F-100 trucks - Ford Truck Enthusiasts Forums



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Rear axle ratios in 57-72 F-100 trucks

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Old 09-30-2014, 10:33 AM
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Rear axle ratios in 57-72 F-100 trucks

I want to put a 3.25 rear end in my 52 F-1 and the chart shows the 57-72 F-100 is the best fit.
Do they have a tag to determine the ratio or must you count turns?
Does the 57-72 F-100's use several different ratios?

I noticed on the rear end article on the blog that the 57-72 has a 5x5 hub bolt pattern but later when they talk about swapping axles they mention the 57-72 has 5x4 1/2 axles.

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Old 09-30-2014, 10:53 AM
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I think there was a problem converting fractions to the font used in the article. 57-72 used the same 5 @ 5.5" pattern as stock.

3.50 was the standard ratio for those years in F-100's, very common to find them. Thee are several different style of axle bearings used, different spline counts on the axles, etc. If you're going to haul Mahindra short blocks in your truck, might be worth looking for a Big Bearing, 31-spline axle. If you do a websearch there are literally hundreds of sites for the 9". Note that in the Mid-'60's they widened the brake shoes from 2" to 2.5", no downside to that except that you can't re-use your Dana 44 brakes. E-brake still hooks up the same.

I have a 3.25 center section in good shape, not proud of it either. Too bad I didn't know you needed one a month ago!
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Old 09-30-2014, 11:18 AM
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Rear axle ratios

Ross,
I am kind of guessing on the 3:25 but with the stock 302 except headers & mild cam and C-4 but I cannot touch the gas peddle without spinning the rear tires. I don't have the bed or any sheet metal on it but the rear axle seems too low. I am not going to use the truck except for running around town or possibly on the road some, no hauling, etc.

I had a 62 Ford back in the 60's with a 2.90 and it was pretty much of a dog.

Maybe I should wait until I get all the metal and bed on it and then see what I have.
Thanks,
Bill
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Old 09-30-2014, 11:44 AM
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Rear End Widths

My knowledge is the 57-72 ford truck rear axle is 5-5 1/2, gear ratios varied to vehicle the norm was 3.50, 3.89 I believe also was common, 28 spline for peg leg and 31 spline on the posi.
I took one out of a 65 ford truck it had the 3.89, changed the pumpkin to 3.23. Took my 56, 283 SBC, 350 turbo trans, out without rear sheet metal and could spin the tires for a complete block, put the sheet metal on and she settled down.
Tire diameter plays a big role here. I was running 28" rears.
On the freeway w/3.23 it just purred down the road, went to yosemite and it pulled the hills like a dog and ran a little hotter.
Pulled the pumpkin and put 3.50's in at this point I felt I had the best of both worlds, freeway and hills.
In my panel I put 3.73 posi. I have a 700r-4 and 29 plus diameter rear tires, so I figure this to be good
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Old 09-30-2014, 12:38 PM
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I think down at your altitude, Bill, and as flat as TX is, 3.25 with a 302, C4, and A/C should be just about right. Like Gerry says, depends too on your rear tires. Mine are 235/75-15, and measure out to have a 28.1 rolling diameter. With the flathead and lots of hills here, plus altitude, 3.50 is all I can pull. I tried the 3.25 and it was a dog with the 3-sp. You have near double my HP. Let me know if you're interested in that pumpkin.
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Old 09-30-2014, 09:37 PM
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When I got my 54 it had a 9 inch with 2.92 gears and 1-3/4 brakes. The 2 dimples and flat band indicate late 60s or maybe 1970 F100. On wet pavement it just sizzled one tire and ring gears less than 3.25 won't fit on limited slip carriers so I replaced it with a '79 Explorer 8.8 with limited slip 3.73 gears. No more sizzling one tire and with my 700R4 and 235/65R17s it purs at expressway speeds.
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Old 09-30-2014, 10:20 PM
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I am running a 3.25 open rear 9" behind my 289 and C4 with 275/60/15 tires. It turns around 2100rpm at 60mph and has plenty of go around town. I have been happy with the combo.
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Old 10-01-2014, 11:25 AM
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Thanks for all the info and suggestions on ratios and keep them coming.
Think I better get my F-1 street driveable with all the metal on it and see what I have.
Probably end up in the 3:25 to 3:50 range.
Should I try for a limited slip if possible?

TractormanBill
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Old 10-01-2014, 11:37 AM
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Go to the West Coast Differential web page and get on their gear calculator you can cal. your tire dia. then go to the rpm cal. and with gears,tire dia. and mph you can see what rpms you have with different gears and tire size.
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Old 10-01-2014, 01:47 PM
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If I had a peg leg or an offer I could not refuse, I would use it. If I had to purchase I would do the posi
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Old 10-01-2014, 01:58 PM
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What Fords have the limited slip rear ends that would fit under my 51 F-1 which I understand is about 61" wide?
TractormanBill
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Old 10-01-2014, 02:29 PM
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Click on the rear end width line in my above post it will tell you the widths of different fords.
The limited slip was an option so it would be hard to tell you which actual one has it. I would stay in the truck rear end, I am not positive as to the 51, but it is a direct swap in the 53-56.
If the third member has not been removed there should be a metal tag that will tell you what it is.
Google Identify ford 9 inch rear end and surf the sites, you will find the info.
I will see if I can find my info and will relay that to ya, maybe someone else will come on and have it
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Old 10-01-2014, 02:32 PM
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Kevinstang's Ford Nine Inch Differential Page +

If you get a rear end it and does not have the gears you are looking for, you can always find a third member that is correct. Just remember to verify the spline count on your axles match the third member

Last edited by gerrymoe; 10-01-2014 at 02:36 PM. Reason: additional info
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Old 10-01-2014, 02:45 PM
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Old 10-01-2014, 06:40 PM
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If you get a pre 71 F100 axle housing, which will bolt right into your truck then you will have the right width and you can put any ratio 28 spline 9" center section into it. You can use the brakes that came with the housing or convert to disk brakes and it might just look like this.

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