I have a 74 F250 4x4 sitting at home. It has the factory D60 rear and a HP D60 swapped in up front as well, but the gears don't match. The rear gears are 4:10's and the fronts are 3:54's I think. I'm pretty sure the front axle is swapped out of a late 70's ford 1ton. I'm sitting in Iraq at the moment and can't figure out the answers to my questions for myself, so I'm going to ask you guys. What are the spline counts on these axles? I plan to order a detroit locker for the rear and matching gears for the front, and possibly a selectable locker as well. I need to know the spline counts so I can order this stuff before I get home (a family friend is going to be kind enough to do the work for me so I can enjoy the truck when I come home on leave instead of having to burn up a day or two wrenching when I could be wheeling instead.) Just in case this info is pertinent, it has a stock 360, NP435, and divorced tcase. Gotta love the highboys! Also, I'd like to thank you guys in advance for your help!

 

Thank you for your sevice forst of all.
Second, your high pinion front D60 will have 35 spline inner axles and 30 spline outers. These outers are smaller, and are the weak point of this axle, but for traction aid purposes, the axle spline count is 35.
As for the rear, this is where things get interesting. You will have to really look at this axle. If this axle is original to the truck, it is quite possibel that you do have a 60 and this is a 30 spline axle. However, this is possible that it has a coarse spline unit, and even more possible that you have a D61.
Some slight differences here, but one thing is for sure. The best or largest axle apline count will be 30 spline, and this is not very strong, and will not justify the expense of a Detroit locker. Mnay have installed the locker in these and they have failed, only to break an axle, and then have to go look for a stronger one.
Save yourself a little time and money and consider something in the 1.5" axle size (35 spline).
The entire axle will be stronger and will not have to be changed any time soon.
Hate to see you spend the money on something that will have a very high failure potetential.
Consider a decent D70 with 35 spline axles, not a 32 spline unit, or perhaps other suitable replacement. You will be happier in the long run and you will only have to spend money once.

 

Alright, so I'm now shopping for 35 spline rear axles as well as a locker. Hahahaha. The list never ends! Im guessing that swapping in 35 spline axles isn't as easy as it sounds. I'm guessing that some kind of machine work is going to have to be done? New axles seals and.....

 

The 35 spline axle does not fit throught the spindle of the D60 rear end. It is possible to enlarge the hole in the spindle, and use 35 spline axles along with the appropriate carrier for the 35 spline axles. This is actually an alernative. (I run a D60 with 35 spline axles) but it is not an easy, not cheap solution.
The easiest solution is to run a 35 Spline D70, Sterling 10.25 or Gm 14B.

Yu are correct, this process never ends. The suggestion of a stronger rear axle is a good one since you run the risk of breaking the D60. These parts are not interchangeable with the larger axles so if you decide to upgrade later you will have wasted money. Been there, dont that.

Some of the above axles are almost bolt in, and will undoubtedly require some drivilaine work, or at least a u-joint change. Bigger is better when you are dealing with alxes and the world of lockers.
Many topics regarding the rear axle swap. The D70 seems to have some popularity, but beware some D70's have smaller axle shafts than others, so verify that you get one with 35 spline axles. This provides you with the best bang for your bucks, and will make field repairs much easier. 35 spline axles are not all that bad to find.