Thread: Narrow The Rear Or Larger Backspacing

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Hello everyone,

I am a new member to the club and have also just purchased my first Hot Rod on tuesday. The car is a 31 Ford 5 window coupe. The car has a stock 73 ford mustang 9" rear. The wheels on the car have a 3.75 backspacing. With this combination in place, the tires protrude out approx. 5" outside of the rear fenders. There is approx. 4-5 inches of space between the inside of the tire and the inner fender well. What I want to do is move the rear wheels in as much as possible. With this in mind, what would be the best thing to do? Should I have the axle narrowed or find a wheel with a backspacing that would bring the wheel in where I want it.

Thanks.

Bart

Originally posted by BARTS31
Hello everyone,

I am a new member to the club and have also just purchased my first Hot Rod on tuesday. The car is a 31 Ford 5 window coupe. The car has a stock 73 ford mustang 9" rear. The wheels on the car have a 3.75 backspacing. With this combination in place, the tires protrude out approx. 5" outside of the rear fenders. There is approx. 4-5 inches of space between the inside of the tire and the inner fender well. What I want to do is move the rear wheels in as much as possible. With this in mind, what would be the best thing to do? Should I have the axle narrowed or find a wheel with a backspacing that would bring the wheel in where I want it.

Thanks.

Bart

welcome if money is not problem narrow the rear end, that will give you more choices of wheels and the deep wheels looks best.

Here is a picture of the back showing the protruding wheel

and the other side. Bye the way any idea of what I should expect to pay to have the rear narrowed if I go that way?

I agree with lt1s10, the narrowed rear end would look best.

What I should expect to pay to have the rear narrowed ???

Originally posted by BARTS31
Here is a picture of the back showing the protruding wheel

thats a nice looking car to have the tires protruding like that. you got to get those wheels up under the finders. been awhile sense i narrow a dif. and i did the labor myself, but the axels was around 300.00, but im sure theyer more than that now. somebody will let you know.

Here this might help ya, I put the 8 inch maverick rear in mine 56.5 wide and it holds up just fine....
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

Neat looking rod. Believe it or not that's how we use to set them up back in the 60's with the back wheels out. I also agree, go with the narrow rear.

If you change the backspacing that much, the rear wheels will look just as odd as the protruding tires - at least in my (not so) humble opinion.

I agree with HWORELL, I do not know know the exact cost of narrowing the rear, but I got a low mileage 8" rear from a '74 Maverick for $175 and then I purchased wheels with 3.75" backspacing to fit the 66" width of the A fenders. Keep your 3.75" backspaced wheels they are just what you need for a Maverick rear. I have 735/75/15 rear tires and they are just 66" shoulder to shoulder on the outside of the tires and so just fit the fenders and are actually pretty big tires. I don't know if it is hard to find Maverick rears, but the yard in which I found mine had three and I picked the one from a '74 with only 68K miles from a 302 with the five lug drums.

Don Shillady
Retired Scientist/teen rodder

Originally posted by Henry Rifle
If you change the backspacing that much, the rear wheels will look just as odd as the protruding tires - at least in my (not so) humble opinion.

the reason he would spend the extra money on the narrowed dif. is he gets to choose the backspacing he wonts and then cut the dif. accordingly. **) **)