we have a little 66 mustang coupe we're wanting to fix, and convert from 4 lug to 5 lug wheels. will an 8" from a 66 fairlane bolt right under and fit in the spring pads? also, can you do the granada disc swap on mustangs, too?
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NMCB 28 Seabee Battalion

The rear axle with not work without modifying it but yes you can do the granada disc swap.

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Originally posted by Sorno:
The rear axle with not work without modifying it but yes you can do the granada disc swap.

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I think you'll find the Fairlane housing to be about two inches wider. I'm not sure about the spring pads. I think the Fairlane housing will be the same width as the 69-70 Mustangs.
The 57-59 full size passenger car uses a 57.25" wide 9" rear which should be the same as what you want but has the small axle bearings similiar to a 65-66 Mustang 8" axle. That allows the 65-66 8" Mustang axles and bearings to swap right in. Mustang 8" backing plates and drums can be used too. This is a good housing to swap from a 8" to 9", especially if you want to use your old axles, bearings and brakes from an 8".
I'd wouldn't think the Mustang 8" housing would be too difficult to find but of course I haven't looked for one for quite a while.

we have a junk 58 ford car. so the backend under it is the right width for the mustang?
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NMCB 28 Seabee Battalion

If it's a full size Ford, yes, the 9" housing will be the same width as a 65-66 Mustang and the spring mounts should even line up fine too. I had a friend who did this very swap a few years back. He did start with a V8 car with an 8" and changed it to a 9" but I'm sure the 6 cyl cars will interchange too. It won't take much to measure both and see if it will work.

thanks ron, that sounds like that's my best approach then.
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NMCB 28 Seabee Battalion

Howdy. I don't know how the paste will work, but the url is at the top. I don't know if it still works. It's a good database on Ford 9" axle sizes for a wide variety of cars. - Scott

http://dfwmotorsport.com/Fairlane/9inchrearends.htm
Year & Model Axle Length Notes

1965-1966 Mustang 57.25 inches
1967-1970 Mustang 59.25 inches
1971-1973 Mustang 61.25 inches
1977-1981 Versailles 58.50 inches
1967-1973 Mustang, Torino, Ranchero, Fairlane 59.25 inches to
61.25 inches
1957-1959 Ranchero and station wagon 57.25 inches
1966-1977 Bronco 58 inches
1977-1981 Granada/Versailles 58 inches
1967-1971 Comet, Cougar, Mustang, Fairlane 59.25 inches
1971-1973 Mustang 61.25 inches
1964 Falcon 58 inches
1967 Cougar 60 inches
1967 Fairlane 63.50 inches coil springs
1972 Ford Van 3/4 ton 68 inches
1973-1986 Ford Van 3/4 ton 65.25 inches
1957-1959 Ranchero and station wagon 57.25 inches narrowest 9" housing
1966-1977 Bronco 58 inches 5-on-5 1/2 inch diameter bolt circle
1967-1973 Torinos, Rancheros, Fairlanes 59.25 inches or
61.25 inches
1967-1971 Comets, Cougars, Fairlanes 59.25 inches
1975 Mustang II 8" 57.00 inches
1974 Maverick 8" 56.50 inches

Where To Find The Nine Inch Rear Axle

1967-1973 medium and big block Mustangs and Cougars 1966-1971 Fairlanes, Torinos, Montegos, Comets, and other Ford intermediates with big blocks.
1957-1959 V8 Fords and Mercurys
1977-1981 Lincoln Versailles & Trucks

Types Of Nine Inch Axle Housings

1967-1973 Mustang/Cougar - light duty, thinnest housing material, small axle bearings, 28 and 31 splines.
1957-1968 passenger car and 1/2 ton truck - medium duty, stronger than Mustang type, 28 and 31 splines.
Ranchero/Torino - heavy duty thick wall housing, 3.25 inch diameter axle tubes with flat tops.
1969-1977 Galaxies (coils), Lincolns (coils), and late pickups (leaf)- 3.25 inch diameter all the way to the backing plate, coil housings have upper control arm mount

How To Recognize Nine Inch Housing Centers

1957 - no dimples, flat center band up the center of the rear cover, bottom drain plug.
1958-1959 - two dimples on back of housing, flat center band, some had drain holes.
1960-1967 - two dimples, flat center band, oil level hole in back cover.
1963-1977 Lincoln, LTD, Thunderbirds had 9.375 inch centers, housings were cut away at the gasket surface for ring gear clearance, one curved rib at the front top portion of differential, strong but no gears.

Tip On Shortening Nine Inch Axles

1972 and earlier 31 spline axles have the ability to be shortened.

28 spline axles are tapered and cannot be shortened and re-splined.
1973 and later cars have a 5-on-5 bolt circle and the axles cannot be shortened.
1967-1973 Mustang axles can be identified by wheel flange:
Oval hole = 28 splines.
Two large holes and counter-sunk center = 31 splines.
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66 Fairlane GT
Daily Driver / Survivor