3/4T Axle Swap

[bighead]

Can anybody tell me why the swap to the 3/4T axles in a 1/2T is popular?
I'd like to be able to take my new project 1972 K10 into the mud or sand from time to time. Do I need the heavier axles for occasional offroad use or would it be better to stick with what I have? Also, is it pretty much a straight bolt in conversion or are custom parts needed? Thanks for your help, big

[1969k10stepside]

If you use 67-72 3/4 ton axles its a bolt in job.If you use a 73-87 type axle the front will work no problems but the back will need spring perches and shock mounts relocated.I planned to do this but IMO its hardly worth the money unless you get them cheap or free.Then you also have to get some 8 lug rims for your tires..Anyway I decided if I was going to swap axles I would atleast upgrade the front to a dana 60.I dont think some people realize that really when you put 3/4 ton axles under your 1/2 ton your really only upgrading the back.The front axle is the same for the most part.Now,yes the rear axle whether it be a eaton or a 14 bolt is stronger than a 12 bolt,but the front might as well be beefed up too..So,if you cant afford a dana 60 front,do the 3/4 ton conversion if you are going to be abusing the axles.The tire size,etc affect how long the stock axles will last.If you are not going to run over a 33 or so the 1/2 ton axles might last but the 3/4 ton axles would be better..If you plan to have over a 35 inch tire or so and you plan to wheel it alot the one ton axles would be best.

Dustin

[eedgell]

1969k10stepside is right on the money yet again. I agree.

[DirtyLarry]

I borrowed this picture from 85 C-10's broke truck thread. This truck is only a 2wd but you get the idea why semi-floating 10 and 12 bolt rear axles are the fuse of the driveline and are flat out dangerous….especially behind decent HP or spinning large tires. I don’t know if you have ever seen a full size truck with large tires have a rear axle separate from the vehicle but it is not pretty and could be deadly.

A strong full-floating rear axle gets you home alive, a Dana 60 front axle gets you home with the convenience of 4wd if you should break something in the front Dana 44. I have never broken a singe Dana 44 front axle part but I also wheel with finesse. I have noticed those that break a lot of Dana 44 (or even D60) parts have driving styles or wheeling styles (playing in mud) that leave toe nail marks in the floor boards. Watch….I’ll probably blow up my D44 next weekend on our next trip now that I said that.

[Zoomad75]

Better go knock on wood. Your last outing was not without problems.

As far as 3/4 ton swaps go, it's really getting a full floater out back to avoid the results of the pic that larry posted. Break an axle shaft in a full floater and the hub keeps the wheel on the axle. Keep in mind if you break a 14 bolt axle shaft you either have some SERIOUS power, lots of gear reduction and a heavy right foot. I'm not saying they can't break, but it sure takes a lot to snap one. 10 or 12 bolts, not so much. I watched a guy snap a 10 bolt rear shaft on a 84 k10 with a wheezy worn out 305 2bbl trying to do a burnout on wet pavement. Couldn't do it until 5 of us lifted up on his rear bumper, unloading his right rear tire. As soon as it started spinning, we let go. The tire made one more revolution and stopped with a crisp metallic *snap*. DOH! Now it wouldn't move. We dropped it into 4 hi and he limped a couple blocks home with a guy in the bed shoving the wheel/axle/drum back into the axle when ever it started walking out.

I'm still running the 1/2 ton 12 bolt in my K5 with 35's. One important key to it's survival with my spastic right foot, no locker or posi. If it's not locked up the stress on the axle shafts is much, less. If it's stuck, I take the hook. I won't waste any money trying to improve my 12 bolt. I'll save it and buy a 14bolt for $100 or less and swap 8 lug hubs up front. By the time you spent all the money for chromo 12 bolt axle shafts and a locker, you could have bought a $100 14 bolt and changed the wheels out for 8 lugs that fit. Shop smart and you'll find a 14b with the same ratio so all you have to do is changes hubs/rotors to match the 8 lugs in the rear. Save $350 or so more and then you can install a Detroit locker without replacing the carrier (as long as you didn't buy one with a gov-loc, which then you need to buy a stock open carrier).

D60's are sure nice to have, but every joker thinks they are worth thier wieght in gold that has one to sell. deals are out there, but if your just doing mild to moderate wheeling a D44/10b can live without being locked and using a little restraint with the loud pedal. It's all dependent on what your plans are for wheeling and the truck buildup.

[earl87gta]

With the front dont forget stoping power the 3/4ton front has larger routers and a little more stoping power then the 1/2 ton.

[DirtyLarry]

Your right Earl..."A little more stopping power" but not much more. The ½ rotors and ¾ ton rotors of that era still use the same brake pads and calipers. Yes, the rotors are slightly bigger in diameter but not much worth writing home about.

By the looks of some posts lately in threads in this forum on the axle subject it seems some people may not have a full understanding of the main difference between full-floating axles and semi-floating axles and why/how there is a strength difference. There seems to be a misconception that ring gear diameter is the main difference, which is not the sole case.

Ring gear diameter may increase with full-floating axles and certainly a major significant player in the strength department, but that is not the primary benefit of swapping in a full-floating axle. Examples of full-floating axles are the 35 + year old Eaton axles found in pre-’73 ¾ tons and the famous “14 bolt” 10.5” ring gear diameter corporate axle (which is still manufactured today by American Axle Manufacturing as the AAM 267 MM axle found in back of the current 2500HD Silverado/Sierra trucks, heavy GVWR Express/Savana vans with 6.0L engines and Dodge Ram platforms) as well as the big 11.5” axle found in late model GM trucks with an 8.1L/Dirtymax diesel or Dodge Ram diesel 2500’s or gas/diesel 3500’s.

One thing that makes older Dana 60’s confusing is the fact pre-’72 GMC Dana 60’s came in the semi-floating and full-floating flavor. My 1968 2wd 396 BB 1500 series GMC came with a factory semi-floating Dana 60, which was pretty rare at the time. Semi-floating Dana 60’s in 80’s and later Ford and Dodge trucks and vans are NOT rare but actually very common. Chrysler used semi-floating D60’s in their serious muscle cars much earlier.

When talking 1981 or later ¾ ton GM trucks you have to be careful as Generous Motors started using a semi-floating 9.5” 8 lug axle which also has a 14 bolt differential cover bolt pattern (that is not a whole lot stronger than the ½ ton axles in the grand scheme of things). The whole “14 bolt” axle nomenclature is misleading to the uninformed.

It get’s more confusing when talking trucks of the Millennium as you have 2500 series trucks with semi-floaters (GM 2500’s LD prior to 2003) and 1500 series trucks with full-floaters (current Dodge MegaCab 1500’s) thanks to the crazy marketers in the extremely competitive truck market place that are endlessly looking for loopholes with CAFE standards while trying to be the segment leader in a given GVWR range.

Anyway, a picture is worth a 1000 words and below is a very old picture of a semi-floating axle comparison to a full-floating axle. If you study the picture and really think about it you will see why the hot ticket (and priority 1 over a D60 front axle) is to swap in a full-floating rear axle…..not necessarily a ¾ ton axle….but a full-floating rear axle. Full-floaters are a lot safer when spinning large meats.

Imagine your big old lifted Chevy with 38” tires on FOX News resting on it lid with 3 wheels pointing skyward in the middle of I-75 while the right rear axle shaft/drum/wheel and tire assembly is poking through the windshield of a tour bus across the highway that is full of old Baptist ladies from Mississippi on their way to the pretty hat convention in downtown Detroit. That really happens to dudes that over tire their axles! I saw that on the news once when I live in Detroit!