I have a rear D70 U-1 with the BOM saying it is from a F350 stake bed (it came out of a 84 F250. I have heard from from a few people not to use the 70U because of the undersized pinion bearing but the ring gear is 10.5 with stock 1.5 inch axle shafts with a 35 spline count. I would think the pinion should be stronger than my D60 rear that is in the truck now? If so it would make a good upgrade. So why are some folks saying dont build a U?

My truck is a 79 F350 SC with a 500 hp 460 and a C6. I also have a 79 F350 standard cab with a fresh stock 400. I got the axle for free but it will cost a lot to build with gears, locker, and disks.

 

Worthless. Sell it to me.


Yes a D70U has undersized bearings and is the "weakest" D70 as far as pinions bearings go but its still much stronger than a D60. It has 35 spline 1 1/2" shafts and a 10.5 ring gear. I really like it because its smooth bottom so there is nothing to hang you up or slow you down. I seriously doubt you will be shearing pinions with 500hp and anything under 44" tires. Dana 60s really arent as strong as people think.

Im going to build a Sterling 10.25 if I cant find another D70U for my 553" BBF and Im expecting 625-650 hp and 700+ ft lbs on 38.5 tires

 

MAny many versions of the 70, but just because it is big, does not make it strong. Just as any other axle, it can only be as strong as the weakest portion.
Dana 60's catch a bad wrap for being weak units simply because in stock form, they have small axle shafts. How is it that everyone wants or needs a D60 front, but will not run one in the rear? Perhaps because it is cheaper to build a larger axle perhaps, but maybe the bandwagon simply has folks thinking that the 60 is a pile.
Having such a small pinion might be a problem if the Hp's get high enough, or the tire size gets large, and this is entirely compounded by the addition of a locker. Now the load of both wheels are being supported by the pinion. A giant ring gear probably has a chance od survival, and really have rarely seen the D60 fail at the ring gear, or pinion.
Since everyone believes that a 60 up front is so great, I just do not see why they get such a bad wrap in the rear.
As far as the 70U, because of the small pinion, you may not find many advantages over a smaller axle. At least with a locker, the axle still works, but with a broken pinion, this just makes for along day on the trail.
While I understand why a D60 wearing stock shafts has a fair chance of failure, i also fee a D70 with its smaller components still has the same potential.
Here is everything you will ever want to know about the D70(s)

http://www2.dana.com/pdf/5312-9.PDF

 

Maybe because D60 rear axle shafts are 1 3/8 at their thickest point and D60 fronts are 1 1/2" at their thickest point. Comparing a stock D60 rear to a stock D60 front is like comparing a D60 front to a D44 front. The shafts are the same size .....1 3/8"

 

Oh...BTW...Ivan runs a 70U with his 557 stroker over 600hp 44" Boggers (sometimes Ags) and lockers.

Ive never heard of him snapping pinions

 

Not all Dana 60 fronts have non tappered shafts, so not all of them are as trong as most folks think.
A locker for a 60 rear is available up to 40 splines, and axles are not that expensive. A Dana 70 Locker really puts things back onto an even playiing field, considering many guys have to run out and buy a D70, but already have a 60. Some machining has to be done to the spindles to get larger thata 35 spline axles in the rear, but is pretty strong after that.
Any axle will take some money to get right,my only point was that the rear 60 is not the junk that most portray them to be. Stock VS stock, they all have thier weak points, and are all subject to carnage at some time or another. That is just part of what we do.
Building a unit that has a smal component like a smal diameter pinion is not something I would run right out and spend money on. Not when there are other options that would not cost any more money. Heak, shaving the axle keeps the bottom from getting caught on anything, and just because a smal group of guys can get one to survive, does not necessarilly mean that it is the rule and not the exception.
Heak Monsterbaby runs a D44. Does this mean that we should run out and scrap the 60's and buy 44's just because we know of one that survives?
I mea the whole reason to go with the weight and mass of a 70 is for strength right? So installing one that has a weak link seems to be counter productive. Not saying it can't survive, just pointing out why they are not desireable.

 

Im going to break this down line by line. Stratus...post this exact topic in the offroad and 4x4 forum for additional info. Not all the guys there visit this room.


Yeah I realize that but if you read my post I said "at the thickest part"

Wrong! 40 spline D60 stuff is God awful expensive. You can litterally build a D70 D80 Sterling or whatever complete with brakes for what the spool and shafts cost not to mention the machining.

Have you ever priced the tool that bores the spindle? There is a guy on pirate that sells them and he gets $450 Why pay that when a D70 Detroit cost $545 I have checked around and NO machine shop in my area has one.


If it cost ~$1000 (500 locker 200 gears 200 install kit 100 misc) to rebuild an axle (Sterling D70 D60 or whatever) Why not build the strongest one possible when you know you are bringing 500hp and larger tires to the table. When it comes down to it, it might cost $50 difference between a 3/4 ton and 1 ton axle

That doesnt deserve my comment.

D60s are NOT as strong as even the weakest D70. A D70U has more ground clearance than most shaved 60s. D70U have been tried and tried again by numerous people on this site and pirate. If Ivan engine and ags arent busting pinions Id say it will hold up to almost anything. Its far from "a small group of guys" that run 70s or Sterlings. Its everyone! Its everyone who has big cubes big tires and likes to play. A D60, even one with chromo shafts, WILL NOT hold up to 500hp+ and 38+" tires for very long and why spend $2000 on a 40spline 60 or $1500 for a 35 spline 60 when you can build the 70 for $1000.
Monster and others who run D44 in mud bogs are going in a straight line. Ive got a buddy who runs a D35 due to weight and it holds up. Straight line mud bogs are NO WHERE NEAR as hard on parts as turning the tires or stop starts. If monster turned his tires and punched the gas...44 = boom

Doesnt weigh that much more...40lbs maybe. Like Ive said like 5 times before the weak link of a 70 is still stronger than a 60. I dont know what rock you crawled out from under but in heavy trucks like 73-79 Ford trucks running 38"+ tires and big power a 60 just wont cut it long.

I have a 460 dyno'd at 390hp at 4500rpm and 532ft lbs at 2000rpm (that translates to ~500hp and ~600ft lbs at the crank) 38" Swamper SX 4.56 gears and detroit lockers and I bust stock 60 shafts like twigs and Moser wont warranty any more of their alloy shafts. Im building a Sterling out of necessity but wish I had a 70U to build. Well actually I wish I had a Dynatrac 80 but I dont have the 6 grand.

 

Oh even better. Further reading has discovered that you cannot bore the stock spindle to accept the 1.7" 40 spline shafts and you must convert it to semi float.

I only found 2 companies that sell 40 spline stuff
Moser $2200
Mark Williams $2700

Cone and CTM sell 35spline 300M Fullfloat shafts and they cost a grand

 

"the weak link of a 70 is still stronger than a 60."

I think it all comes down to this realy, which is the question I had. Why are people saying dont build a 70U?

I am also wondering what was the reason for marketing a D70U? Was it for better economy? It must be lighter than a standard 70 , I'm sure it is lighter than an HD, and if it is lighter and still holds up to a locker with 600 hp pushing 44" tires why would anyone want a standard 70 or D70 HD?!

I have been thinking about this for a long time (ever since a friend gave the 70U to me for free). It seems like people see the "U" (undersized Pinion) and think to themselves "I cant have anything undersized in my truck", but a D70 HD has an "undersized" pinion next to a D120.

I wonder, if the D70U had been called a D70 LTPA (light truck performance axle) would everyone want one?

 

Got things all fired up.
But we are getting no where fast, and that is no good.
The biggesyt point that I was trying to make is that the 60 gets a bad wrap for being a little axle, and it can, and has proven to be a reasonable axle. Because of the bad wrap they are almost free, and a worthy axle with a few modifications, Certainly worthy of handling reasonable horsepower and tires. Really look at how many flock to the Dana 60 front axle, and love them. Why would a D60 rear with 35 splines not be worthy of the same respect? Poor thing gets a real bad wrap from being used with 44" tires and in stock form. Guy can have a bone stock front 60 with tappered non chro-mo shafts, and everyone thinks it is the next greatest thing since sliced bread, but if a guy has a 60FF 35 spline rear, it is huge criticizm time. Just do not get it.
At any rate, that does not take anything away from the D70's. Even the U has a reasonably large pinion diameter at 1.71" or 1.72" and that is pretty darn big. There was never an argument that it is not strong, just not as strong as say a 70 HD that would have a 1.75" pinion. Does that make it weak, no, but it does make it not as strong as it can be. Perhaps this explains the desireability of the larger HD units.
These are very large axles and built to survive, right out of the box.
Even the smaller of the large axles should very well be up to tha task.

 

So the "undersized" pinion in a D70U is only .04" smaller than a D70HD? That does not seem like a very big difference when it comes to just pinion size. Heck with the smooth bottom of the D70U vs. the massive webbing of the HD I think I would rather have the U to keep from getting hung up on the rear dif.

If I am wrong someone PLEASE set me straight, but so far I like the 70U better, and I know the cost of building a U is less than an HD.

what is the pinion size of a rear D60?

 

75F350
I will agree that a 35 spline D60 FF is a very strong axle. My point is that it cost so much to adapt a 30 spline axle to accept the 35 spline shafts that its pointless.
You have to buy or find
35 spline D70 shafts
a 35 spline D60 Locker or spool
buy another install kit
plus either bore the spindle yourself using a $450 tool or find a machine shop to do it for you and be charged God knows what.

When it cost MORE money to build a 35 spline 60 why not build a 70 instead? especially when you have the 70 sitting in your shed for free.
It really doesnt make good sense.

Stratus,
You are exactly right. Guys let .04" sway their vote. Honnestly, if you get in a situation where you are breaking a pinion of almost 1 3/4" does .04" really seem that much stronger?

Do some searches in the offroad forum. These guys here are extremely knowledgeable on stock 73-79 stuff but in some cases when it gets "out the box" the offroad forum can help alot more.

 

whoa, whoa, whoa... are you serious? people consider it weak becaus it is 0.04'' smaller?? Thats messed up! is this the only difference between a 70U and a 70HD? or is there more to it? i can get a 70U for free, but i thought it was a pile, i might just go get it...

 

It is not just the smaller pinion, it has to do with the pinion bearing as well. Combined the two will allow the pinion to move under extreme loads. Keep in mind, unlike other style axles, the Dana does not have extreme pinion support, and has to rely on larger bearings to provide proper support. Any movement of the pinion results in a change in gear engagement, and can cause chipped teeth or the eventual failure of the gears. This is really where the Corp 14B shines, and is where much of its strength comes from. In reallity if we are talking about costs. Dollar for Dollar, the 14B makes more sense.
As far as the cost for each axle, Some folks may have D70's in the shed, but most do not, but they do have 60's in the truck already, and other than machining the spindles they can be very in-expensive to build. Machining the spindles is not all that bad however. Finding the right shop to bore a spindle to 1.630", or 1.650" from 1.400" is not that big of a deal.
Regardless, probably an arguement that could go on and on right?
The Dana 60 pinion measures 1.625", 0r 1.630" (reallt can't recall) with 29 splines.

 

it's true Dana Axles have only two bearings where the 14 bolt has 3 but the Dana axles are designed to only need two bearings where the 14 bolt has to have three. Its all about design. I believe the D70 is slightly stronger with only it's two bearings.

I also believe the The D70 HD has a larger ring gear so there is more to the HD than just .04" bigger pinion, but do most guys realy need an HD? now I am starting to think the D70 U with 35 spline shafts and the smooth rear dif is the only way to go!

Someone passed bad info about the D70U many years ago and it has continued to this day in the mind of 4x4 builders. "Undersized " is a relative term. The U is a good axle.

THX for everyones input!