Axle Comparison for the NC4x4 Experts.

bigblockburris

bigblockburris

Well-Known Member
Joined
Mar 20, 2005
Location
Mt Pleasant NC
I am starting an axle swap on a 1967 M715.
I have the front covered (Dana 60) no problem.
I will be running 38"-40" tires.
Rear has me concerned.
The springs on the rear are 54" apart. I have a full width 14-bolt FF out of a 1 ton Chevy truck. Backing plate to backing plate on my 14 bolt is right at 54". Everything I read says you have to run rear disc. Again, no problem, but even disc are close and some people have had to mount the calipers upside down???!!?? The calipers hit the rear springs.
So I gave up on a 14 bolt and found a Dana 60 that was wider. Then a fellow board member brought it to my attention that the axles in the 60 were the weak link and would not stand up to mild 4 wheelin' with that size tire with out an axle upgrade.
I also have a Dana 70HD out of a Chevy Dually. Its draw backs are size (ground clearance), cost of parts, and width.
So my question is.
Which axle?
Corporate 14 FF
Dana 60
Dana 70
Thanks in advance!
BBB
 
Unless its a FF, 35 spline'd 60, there's no reason to run it over a 14 bolt or 70. Have you thought about inboarding the springs? I will say that it'll be extremely stable like that, but it probably won't want to flex too much. With the discs, you might want to grind off your backing plate flanges and weld a disk bracket on there. Because of a straight weld-on disc bracket, it requires less room. Not sure of how big (spring pack height wise) of a spring you're running, whether or not you're using a block, but things like that are what to take into account. Your spring plate will be much more apt to hit the caliper than your actual spring, depending on the location. I don't see how it would be necessary to completely mount your caliper upside down, but more of a 3 o'clock position if you were facing the axle tube with the pinion at a 0 degree angle. If you can clear your spring plate, I guess you could run them at a 12 o'clock. The best way to figure it out is to pick from the 70 or 14 bolt which one you want to run, go ahead and convert it to discs, roll it under the truck with the springs on there, and figure out where your calipers need to go. Disc conversions on a 14 bolt are pretty straight forward, but if your 70 has the 5/8th studs and you're converting to discs, figure out whether or not you want to run wheel spacers. PM me for more info about why that is if you want to run wheel spacers on the 70 and convert it to discs.

Edit - a 70HD is rated for 8,800 ft lbs of max torque, whereas a 14 bolt is rated for 6,242 ft lbs of max torque. The 70 in my opinion is supreme to the 14 bolt in strength and gearing. The only downfall in my opinion is the fact that 14 bolts have the pinion support and a 70 doesn't and you can't get a spool for a 70. But I essentially made my own spool, so that's alright with me.
 
If the 70 is the right width, run it.. it's no worse than the 14 bolt for clearance.. better, I'd think.
 
Just spitballing here, but wouldn't mounting the calipers upside down make a great opportunity to trap air? Isn't the bleeder screw at the top of a caliper for a reason?
 
The M715 dana 70 is actually pretty strong. It has 1.5" shafts, but they are 23 spline. There are a lot of people that run them with 38-44" tires either welded of with a detroit and don't have problems.

Some guys have rigged them to fit a 8x6.5 lug pattern.

As far as swaps go, van-width rear axles seem to be popular, the 14-bolt spring perches apparently bolt-in, but the disc brake calipers still hit the springs and need to be run upside down and vacuum bled.
 
I have a '67 M715 with a built 440 and 38" Boggers that I've wheeled fairly hard on the stock dana 70 that has a Detroit in it and have had no problems. (My weak link has proven to be the TF727 auto trans.) James
 
Why can't you swap the spider gears & run the 35 spline shafts in your original d70 other than shaft length
 
I say go with the Dana 70HD
 
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