I have finally found a pre-72 F-100 axle to swap under the panel truck. It really didn't take that long to find a one, about two years. Patience paid off, I found mine on Craigslist for $75. I had to drive about 200 miles, round trip to pick it up but it was well worth it. When I got to the seller's house he already had it out of the truck waiting for me to load it into my truck. It looked pretty nice, a little surface rust but no major scaly rust you'd expect on a 30+ year old axle. When I got home and unloaded it from my truck one of the brake drums came off. To my surprise the axle had two new brake drums, new shoes, cylinders and all new hardware. Not bad for $75, I've seen sell on eBay, and at swap meets for over $500, in a lot worse condition.

'48 F-4 '48 F-4 '48 F-4 '48 F-4

There are many places on the internet that give advice on swapping the newer 9" F-100 rear axle under the older Ford trucks but the best discription I have found is by Tim Bartholomew, MTflat on many of the truck boards I visit.

Here is his advice on how to do the swap:

First, gear ratios. I have a HD 3 spd and I imagine yours might be the std 3spd unless someone swapped a remote shift HD out of an F3. My 1st gear is significantly different than yours at 3.71 vs. 2.78. 2nd gear is close to the same. But I also run 215/85R/16's so that evens things out some. I can start out in second gear if I ease into it, so it's my guess you could probably get away with 3.08 in the rear. With 3.50 in the back I cruise at close to 65 at 2500 rpm. Personally I think anything between 3.00 and 3.50 will accomplish what you want. The swap: The 9" rears from '57 thru '72 F100's will bolt in with only a few mods.

  1. You'll need new U-bolts to hold the axle to the springs. This will be upside down from the stock orientation. U-bolts can be had at NAPA or your favorite parts house. You'll also need to fab a new bracket for the u-bolt on the bottom side of the springs. I reworked a pair from a parts pickup by drilling new holes in a 2.5x3.5" pattern. (springs are 2" and the axle housing is 3" + the thickness of the u-bolt shank) I think theu-bolts I got were 3"x9" - 3x8 would probably work.

  2. Shock brackets - I just cut the old ones off the 9" and relocated them the same distance from the backing plate that the stock axle had them or find a pair of shock brackets that someone has parted off an F2 (which also has a 3" axle tube) This would solve the shock and the u-bolt issues at the same time.

  3. Driveshaft: The 9" assemble is shorter than the stock Dana by about 1 1/4". My 48 F1 has a sliding yoke on the front of the shaft. I simply went to a local driveline machine shop and bought one off the shelf that was 1 1/2" longer. I've heard some driveshafts are different so you'll need to improvise here. One solution I heard about long ago was to get the differential yoke from mid-70's stationwagons that used a longer yoke??? Or have your driveshaft lengthened.

  4. Pinion angle: This needs to match (opposite) the output shaft of the transmission. The flatheads I've seen are at about a 6 deg down angle so your pinion wants to be at 6 deg up angle. Practically, this isn't too critical as long as you get it close. I found that 5 deg caster wedges from NAPA got me within about 1 deg. Put them between the spring perch and the spring pack. NAPA calls them 'shims' so if you're in need of a pn, it's 704-1168

That's about it. Oh, as a bonus, the backing plates off the Dana/Spicer 41/44 bolted right on the axle stubs of my '65 9" axle. That was nice 'cause I had just rebuilt my brake system. Have fun!

ps. 9" axles from '73-'86ish are about 3" wider than your stock axle you can make this up with backspacing on your wheels if you want to go to the bother. Also 9" axles from '67 to '72 use wider brake shoe for more stopping power. Also your flathead will love 28 spline axles - no need to look for 31's

by Robert A. Jones. All rights reserved.Last updated on April 10, 2008