The Stovebolt Site Forums The Shop Area Driveline rear axle width?

In the process of rodding my 1946 ½ ton I removed the torque tube & rear axle. I am leaning toward a f**d 9” and was wondering about width. The current axle measures about 60 ½”, brake drum mounting flange to flange. Do I want to match that width, or go narrower or wider? I have lowered rear leaf springs in back and I am planning on using a stock sized box. I haven’t decided on stock or 2” wider rear fenders (probably stock,) with a larger tire/wheel in the 17” to 19” range. I know this in a relatively common swap and was wondering what you guys did. Thanks in advance.

my 46 1/2 ton has an s-10 rear that is 53" from backing plate to backing plate and fits well under my truck....(checkout pic)and Im running corvette rally wheels ( 10" rear,7"fronts)with 235/70R/15 tires

Figure out what rims and tires you will be running. The offset of the tire can make all the difference in the world.

The stock 1946 fenders are about 11-12 inches wide. So the goal is to try to center the new wheels in the fenders.

On my 1940 GMC, I went with a 61 inch wide IMCA modified 9 inch.

I am using 16X7 artillery wheels with 4 inches of backspacing.

49 inches for the bed (bed probably closer to 48.5)
+ 8 inches for the wheels (4 inches for each wheel)
+ 3 inches for the tires overhanging the rims
+ 2 inches for clearance(1 inch on either side of bed.
= 61 inches

My measurements should center the wheels under the stock fenders for a 16 X7 wheel with 4 inches of backspacing. At the time I ordered the axle I was considering a 255/70r16 tire. I am now leaning towards a 235/85r16 tire. My truck is not together so I can't send pics of the finish.

I used an S-10 rear end on my '46, because it's on the whole S-10 frame. My wheels are 15x10 with 3-3/4" backspacing, but I tubbed the box slightly as I wanted the wide wheels and I'm running a 31x10.5 tire, which fills the fender and then some. You need to make your decisions about your fenders, wheels, and tires before you choose your rear end width so that it looks the way you want it to. I prefer a narrower rear end so that the wheels have way more negative offset. Whichever you prefer though, but you need to make those decisions first and it will fall into place.

Thanks for the response. Correct me if I am wrong: The difference in width of say a 60” rear end vs. a 62” rear end, with the same sized tires, can be compensated for with wheel offset allowing the same wheel track? If this is true than is the only real difference cosmetic (how dished the wheels are) or are there other reasons why to go with a wider set up? There must be some reason why nearly all modern vehicles have such a negative offset wheel.

Many modern vehicles have very negative wheel offset because of front wheel drive and needing room to fit CV joints and suspension parts up there.

I guess I was using the wrong term: I meant positive offset instead of negative. Negative would be the deep dish wheel; positive offset are the more modern wheels.

Wheels that are offset to far in or out will stress the bearings. Newer vehicles are set up with wider axles and wheels offset inward to take advantage of the bearings properties.

I'm no engineer. The forces placed on bearings by different wheel offsets is out of my grasp.

When you're building a hot rod the track width is whatever you want to get the look you want. Keep in mind too narrow of a width will keep you bouncing in and out of the driving lane groove on grooved highways and freeways.

You need to see what offsets the wheels you want are available in. If you're wanting 17 or 19" wheels and you put too wide of a rearend in you'll be stuck with positive offset wheels, which don't look good on these trucks (in my opinion). Sure, bearing wear will change based on offset, but if you regularly maintain your vehicle this shouldn't be an issue. If you go with a narrower diff you can always use spacers, but going with a wider diff there's not a lot you can do if it's too wide.

My early '47 had a 1956 Chevy car rear end under it, it fit like a glove and I was able to run 8 inch rims in the rear and no tire stick out. The newer S-10 rears are almost the same width and have disk brakes. They are 5 lug on 4 3/4 spacing so you can get a lot of different aftermarket wheels. If your lucky you can get one from a wrecking yard with a no-spin (check the option codes on the glove-box stickers) There is some info on the Chevy Tri-five boards about this conversion. Available from 1995 and up, 8.5" ring gear 30 spline axles, standard for 98+ ZR2's with rear discs

Look in the glovebox at the RPO codes (list of factory reference codes as to what parts were installed on the vehicle).
GU2 2:73 ratio
GU4 3:08 ratio
GU5 3:23 ratio
GU6 3:42 ratio
GT4 3:73 ratio
GT5 4:10 ratio
GQ1 Open Differential Rear Axle
G80 Positraction/Locking Rear Axle