67 Diff width

[stu67]

Morning all,

After a 4 year hiatus i am back on my 67 restomod. Want to get it finished before my second boy is born this January!

I tried to search to forums but couldn't find definitive info. I had a modern diff in my 67, but its noticeably wider than the stock one so normal mustang wheel backspace wont fit. I'm looking to get it cut down to the correct size and just want to confirm the info I've found on the web.

Wheel flange face to face measurement is 59.25inches? I'm going to provide this to the guy cutting and machining the shafts, so i want to be extra certain.
My other question.....is there any offset on the pinion that he has to be aware of, ie. does he need to cut more from one side than the other or is it symmetrical?

Thanks in advance, i only want to do this once so want to get it right first time!

Cheers, Stu

[Shaunp]

got a feeling they are like 59, about the same as an XY I think
You normally only cut one side the length is close

[Nuts]

This is probably accurate.

Ford Rear Dimensions
by Dave_C and the Fordnatics mailing list.
Here is a list of rear ends that I picked up some time ago on the Fordnatics mailing list.
These measurements are from flange to flange. Subtract 5" for bare housing length.

65-66 Mustang 57.25 inches
67-70 Mustang 59.25 inches
71-73 Mustang 61.25 inches
77-81 Versailles 58.50 inches
74 Maverick 8" 56.50 inches
75 Mustang II 8" 57.00 inches
67-73 Mustang, Torino, Ranchero, Fairlane 9" 59.25 inches to 61.25 inches
57-59 Ranchero and station wagon rears, 57.25 inches
66-77 Bronco 9", 58 inches
77-81 Granada/Versailles, 58 inches
67-71 Comet, Cougar, Mustang, Fairlane, 59.25 inches
71-73 Mustang, 61.25 inches
64 Falcon 58 inches
67 Cougar 60 inches
67 Fairlane 63.50 inches (coil springs)
72 Ford Van 3/4 ton 68 inches
73-86 65.25 inches
57-59 Ranchero and station wagon 57.25 iches (narrowest 9" housing)
66-77 Bronco 58 inches but has 5-on-5 1/2 inch diameter bolt circle
67-73 Torinos, Rancheros, Fairlanes 59.25 inches or 61.25 inches
67-71 Comets, Cougars, Fairlanes 59.25 inches

Where to find the 9" rear axle
67-73 medium and big block Mustangs and Cougars
66-71 Fairlanes, Torinos, Montegos, Comets, and other Ford intermediates
with big blocks
57-59 V8 Fords and Mercurys
77-81 Lincoln Versailles & Trucks

Type of 9" axle housings
67-73 Mustang/Cougar - light duty, thinnest housing material, small axle
bearings, 28 and 31 splines
57-68 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
69-77 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 9" housing centers
57 - no dimples, flat center band up the center of the rear cover, bottom
drain plug
58-59 - two dimples on back of housing, flat center band, some had drain holes
60-67 - two dimples, flat center band, oil level hole in back cover
63-77 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.

Types of 9" Axles
28 spline axles cannot be shortened and resplined (they're tapered)
Some can: 69-73 Mustang and Cougars have a straight 28 spline axle.
72 and earlier 31 spline axles have the ability to be shortened
73 and later 9" (big cars) have a 5-on-5 bolt circle and the axles cannot be
shortened
67-73 Mustang axles identified by wheel flange:
oval hole - 28 splines two large holes and counter sunk center - 31 splines

[stu67]

Thanks gents,

Nuts, this is the post where i got my measurement of 59.25 inches, so seems like that's my lucky number.

Wont only cutting one side offset my diff and pull the transmission shaft further out of the gearbox? I've already attached my bracketry to the new diff so i'll need to take the same length off each side.

[Nuts]

Yes, you will need to cut both sides. The drives shaft needs to follow the centre line of the tunnel. Shaunp may have been referring to the need to cut only one of the axles. The other may fit fine when the housing is shortened. How much do you need to cut from it?

[Shaunp]

No depends how much you have to shorten it . Its not uncommon to cut one side if possible, but its also common to put the short axle on the other side and shorten both tubes that way you only respline one, just depends.

[stu67]

I’m pretty sure it will just be 1in cut off each side, which will be perfect as I can keep all the brackets as they are.

Thanks for your help guys, appreciated.

[Dwayne]

Or leave the diff and just use a different offset on the rims

[stu67]

Main reason I want to get it back to stock is for looks and choice of wheels. The way it is now I’ll have less ‘dish’ on the rear than the front which I won’t be happy with aesthetically. I’d like them to all look the same.

[rkmiller73]

Summit racing is selling a direct replacement reproduction housing with the necked down axle tubes. The photos look fairly good.