Blog

It seems as though the further along we get into this project the faster things seem to go (thank goodness!). We’ve learned a lot about axles and we are beginning to learn a lot about leaf springs/suspension and driveshafts. For now, we will try and impart some of what we learned about solid axles with you…

The Truck
The ’58 Travelall came from the factory with a solid front and rear axle, but we were having trouble justifying the continued existence of these particular axles on this particular build-up. Reasons for swapping out the factory axles ranged from the original drum brakes, funky lug nut pattern (for split rims/wheels) to the general concern that they needed to be rebuilt. These factory axles would have had no trouble distributing the 140 horsepower from the original Black Diamond 264 to the driving wheels. But now the stakes were much higher and with the new GM 6.0L V8 we were pushing 320 horsepower and we weren’t going to chance it. One other small detail: The brand new transfer case output shaft (part of the new GM drivetrain) resided on the driver’s side of the vehicle, while the input on the original IH front axle resided on the passenger side. So, we knew the front axle wasn’t going to cut it.

Dana 44RS schematic (i.e. the new(er) front axle)
Now, when we started this project I thought I knew something about solid axles. As it turns out, what I knew just scratched the surface. To hard-core off-roaders, I was a novice. I didn’t know all the vocabulary or all of the moving parts (and there are a lot of them). To do this right we needed to know the vocabulary and basically how these things worked; both inside and out. So, first, I’ll mention some of the interesting ‘vocab’ highlights, and then what having an axle with those attributes actually means to the end user.

Full Floating
A full floating axle is typically reserved for vehicles designed for severe duty or carrying loads. The axleshaft is allowed to float in the system and does not support the weight of the vehicle (neither of which is true for the more common semi-floating solid axles). So, in a full floating solid axle the axleshafts really only serves to transmit the rotational torque from the differential out to the wheels.
*Another interesting advantage of a full floater includes being able to remove a broken axleshaft yet still have the ability to keep a functional rolling tire on that corner of the vehicle. Pretty cool if you’re off-roading, break an axleshaft out in the middle of nowhere and need to get home.

Image taken from Off-Roader 1999
Reverse Cut: Probably the most misunderstood vocab term we encountered when discussing axles, (even with people in the axle building business). Sometimes people mistakenly referred to reverse cut as ‘reverse rotation’. The term ‘reverse cut’ actually refers to the direction of the spiral cut in the ring gear. Typically used to strengthen the operation of the gear when it is used for a front axle application. Back in the early days, due to re-tooling costs, manufacturers simply used the same gears and housing as an ordinary rearend when building a front axle. These standard cut ring gears were cut in such a way that made them inherently stronger when pushing the vehicle. This practice of using standard cut ring gears in front axles continued until the late 1970s when Dana designed a new axle that would be stronger for front axle use and also provide better driveline angles for the shorter front driveshafts. Reverse cut gears are stronger when used in front axles because of the gear mesh when moving the vehicle forward. I have also heard rumors that lubrication of the gears is better. They also typically provide better driveline angles because the pinion is located above the centerline of the axle, which is commonly referred to as high-pinion.

Image taken from Off-Roader 1999
High Pinion
In terms of ring and pinion strength, the high pinion axle is superior when used as a front axle. When a low pinion axle is used on the front position of a four-wheel-drive vehicle, the ring gear is spun backward. This is important because the ring gear teeth are curved. A simple geometry lesson tells us the convex side is stronger because the load is equally distributed throughout the length of the tooth. The convex side goes towards the load. The high pinion axle uses a reverse cut gear, and when used in a front position, the convex side becomes the drive side again, and the concave side becomes the coast side.
Another advantage of a high pinion front axle is that the driveshaft location being higher due to it’s location; above the centerline of the ring gear. This can be a two-fold advantage, where you gain ground clearance and a better driveline angle. This can be especially important on shorter front driveshaft vehicles. The sharper the angle of the driveshaft the more likely it would be for the vehicle to develop driveline vibrations and/or the quicker driveshaft U-joints will wear out.

Specific Axles Chosen
In the end we ended up choosing a 1979 Ford F-250 Dana 44RS front axle with 4:09 gears (built 1977.5 to 1979). This particular axle is an open knuckle, ‘spring over’ (leaf spring packs sit on top of the axle), full-floating axle with the larger eight-lug bolt pattern and large disc brakes. They also have 3-inch diameter axle tubes with 1/2-inch thick tube walls. Unfortunately for us, those in the business of buying and selling axles tend to covet these axles, which bumps up the price.
This particular Dana 44 was purchased from a salvage yard which bought an entire truck just for the front axle. An even more ironic circumstance came when we decided to try and swap out the original IH front axle for the Dana 44. The 1979 Ford F-250 Dana 44 front axle bolted directly up to the 1958 IH Travelall factory leaf spring packs. I’m not sure what the odds are of that, but talk about luck!
The rear axle chosen was a 2003 AAM Corporate 14-bolt. This particular axle was used on GM 2500 and 3500 Heavy Duty trucks. It too is a full-floating axle with disc brakes.

Next Adventure
Since we were not as lucky with the rear axle as we were with the front, it was time to leave the Travelall in more capable hands than our own. Hands that could shave the ‘bump stop plates’ off the rear axle to make room for new perches. Those new leaf spring perches would need to be welded to the rear axle in the appropriate location (where they would line up directly with new leaf spring packs). New leaf spring packs would have to be custom made to handle the appropriate load at the appropriate spring rate. After some searching we found an appropriate suspension shop who was willing to take on this portion of the project.
Next it’s on to driveshafts, crossover steering, and brakes. Wish us luck, we’re going to need a truckload of it!