I am fixing to narrow my Dana 60 for my drag pick up. I have seen a few guys post on here with old body style d150's. So here's what I have. 1978 d150 step side looking to narrow the rear to be able to fit 15" wheels I'm excited but nervous because I don't want to screw it up and end up having to cut and re weld and buy different axles. In the picture I am posting my chicken scratch with my measurements. I will be running c body brakes and strange h1147 hybrid housing ends to run big ford bearings. They measure 1.3 total width according to strange. Strange also says the length of the axle from the housing end is 2.5 on each side. If anybody has a step side sitting around or has one they have narrowed one for could confirm my measurements or dig up old notes and see what they did to fit big tires let me know. The wheels I have my heart set on are 15 x 15 super tricks with 5 inch back space. Leaf springs are still located in factory location and haven't cut out the bed to tub yet

Can you remove your tires on the truck now so you can mock up the new wheels? If so do that after you get them exactly where you want them and then measure from the back of the wheel to the back the other wheel and call Strange or Dr Diff (better choice in my opinion ) and have them help you get the dimensions correct for the narrowing to fit those wheels Are you going to keep the leaf springs? If so in the stock location or moved in? Maybe coil overs and ladder bars or a 4 link with coil overs may provide a lot more room back there

I haven't bought slicks and tubes yet for these wheels. On a tight tight budget buying one piece at a time until work picks up. But I suppose that would be the best idea. I was planning on running stock location springs since on a pick up you can't move them in very easily. And I want to get it running down the strip before committing to 4 link

I would do the reverse of starting with a clean sheet, measure the width of the stock inner wheel wells to the leaf spring outer edge and the see what width wheel you can fit in there, remember the tires will be at least 1 to 3 inches wider in the section width than the wheel widths are If those 15 inch wide wheels won't fit in with the stock leaf springs in there present location they won't fit with wheel tubs later Plan and measure many times before starting Good luck, take it one step at a time

You may want to consider allowing for aluminum hat disc brakes down the road at some point. The rotors on my Wilwoods are at least 1/2 inch thick or more and 3/8 thicker than the steel drum mounting area. If the wheels you want to run are not too thick at the center you can run spacers for the time being. I have run 1/2 inch spacers for many years, just be sure and stay on top of torqueing the wheels regularly. ESPECIALLY if there are washers that go over the studs. They can deform and lose clamping load. I finally went to 5/8 studs for piece of mind.
Allow at least 3/4 inch clearance on both sides of the tire.

http://www.doctordiff.com/axle-calculator/

Use this when you figure out what the width will be

I'm with Cab, I don't think there's any way you have 18" between the inside of the fender and the outside of the leaf spring in stock location. So unless you are going to change the suspension there's no way those tires and wheels will fit no matter what length the axle is.

I haven't heard of back-halfing a pickup truck, but I think that's where you're headed.

R.

Buy, borrow or bum the correct wheels and tires you will using. Don't have to be new. I recommend using the deepest (smallest backspace) wheels you can get. Get everything out from under the truck. Mock the wheels/tires where you want them under the truck. Measure inside to inside on the mounting surface of the wheels. Start subtracting, rotor or drum thickness, axle stickout, housing end, etc. Also, make sure of where the driveline centerline is in relation to the centerline of the truck to get the pinion offset correct.

Eliminate all the guesswork. Build the rear to the wheels/tires for a perfect fit.

Pretty simple math

77-45.75= 31.25
31.25/2=15.625

15" wheels are usually 15.5-16" measured to the outside lips.

Good luck with that and hope there is zero bulge from the tires.

Well shoot so max would be 14s and it'll still be tight. Guess I'll have to save them super tricks till I invest in back halfing it or tube chassis I spose.