Ford 9 inch
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Joined: Apr 2003
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Ford 9 inch
howdy, ok i have a 88 bronco with a 302. i have the stock rear end with 3.53 gearing i believe. well i want a ford 9 inch with 4.11 gearing. but i dont want the 29 spline i want the 32 spline rear end.
1 how can i tell the difference between the 29 and 32 9inch?
2 do all 9 inch's come with 4.11 gearing?
3 has anyone done this before and have any helpful info for me?
or just any gerneral info at all concerning the issue.
Thanks, David
1 how can i tell the difference between the 29 and 32 9inch?
2 do all 9 inch's come with 4.11 gearing?
3 has anyone done this before and have any helpful info for me?
or just any gerneral info at all concerning the issue.
Thanks, David
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Ford 9 inch
I was under the impression the larger spline number was only 31 but that little descrepancy aside, the gearing would depend on the vehicle it came from. The Bronco's came with the 9" from 66 through about 82 or 83 and were available stock with the 3.55's or 4.11's (customer option). Not 100% certain as to the location, but the axle should have a tag or code on it showing the original gear ratio and whether or not it had any sort of trac-lock or limited slip differential in it. You can check the gear ratio by raising one wheel, putting the truck in neutral, rotating said wheel and counting the number of times the driveshaft (pinion gear) rotates. Then, you can calculate the ratio based on the number of rotations as compared to the number of wheel rotations. By way of some simple math, you can calculate the ratio. I don't know the exact formula but someone does and will certainly impart the knowledge.
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Joined: Jan 2003
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From: SE Texas
Ford 9 inch
Nelly781, all 9" rear truck axles after 1970 have 31 spline shafts, according to my sources. If you have a donor axle that you want to swap into the 88, look for a little tag on the differential carrier. My 84 Bronco has the factory 9" with 3.50 gear ratio, rather rare after 1983. Later-80's model Broncos and F-series trucks had the Ford 8.8" rear axle, like yours and the one in my 88 Bronco, with 3.08 or 3.55 ratio gears. I think the 4.10/4.11 ratio was more common in the truck line, haven't seen any Broncos with these.
It would not be very hard to swap a 9" under your 88, but you need to match the gear ratio in the front axle with the rear in a 4x4. The front axle on the TTB Fords is a Dana44, and uses a different carrier for the 4.10 gears than the stock 3.08/3.55's.
For the simple math test, 3 and 1/2 driveshaft rotations for 1 tire rotation =3.50 or 3.55 gear ratio
I'll put a few pics in my gallery here to look at, Randy
It would not be very hard to swap a 9" under your 88, but you need to match the gear ratio in the front axle with the rear in a 4x4. The front axle on the TTB Fords is a Dana44, and uses a different carrier for the 4.10 gears than the stock 3.08/3.55's.
For the simple math test, 3 and 1/2 driveshaft rotations for 1 tire rotation =3.50 or 3.55 gear ratio
I'll put a few pics in my gallery here to look at, Randy
