Rebuild 1972 K10 12 bolt or swap in 14 bolt Semi Float or Full Float

[1976gmc20]

if I went with a FF axle, could I just run wheel adapters to fit my 6 lug rims and be on my way?

Just convert everything to Full Float and 8 lug wheels and then you can run real E-range truck tires

I've had nothing but trouble with 15" wheels and radial LT tires on half tons. The old 700-15 bias ply did hold up pretty good.

[Mike C]

I would do the 6 lug 14 bolt. And yes, it is that much stronger. The 12 bolt is rated 3300# GAWR and the 9.5" semi-float is rated at 5500#, equal to the Dana 60 in many ways and superior than 30 spline versions.

The 33 spline axles in the 9.5" sf are massive compared to the 12 bolt. I have run a semi-float 14 8 lugger in my Jimmy for the last 15 years. In the previous 15, I went through 4 or 5 12 bolts.

Before the truck was mine it was my dad's. And he hot rodded NOTHING. Drove it like the little old lady. And the 12 bolt broke. And so did the junkyard replacement installed circa 1981. Then when I started beating on it, it seemed to come apart all the time.

Mine has the Gov-Lok in the back still and it actually works OK for boat ramp type exercises that was the primary use for mine when it was a daily. But it's no fun for spinning tires in the dirt or whipping a donut in the snow. I recently bought a Yukon LSD that will replace it at some point. It's on the list...

[TIMCHNE]

The 14 bolt sf is the perfect rear for a half ton 4x4 and the drums are the same diameter as 12 bolt. I ran rallies on the one I had in my 72. The wheel bearings half nearly twice the surface area and 50% larger dia. The pinion stem on a 12 bolt truck is the same as the old 8.2 car 10 bolt 1.48 dia (weaker than 8.5 10 bolt 1.63) 14 bolt SF is 1.88 with massive bearings. They are 4 inches wider so the rear track will be the same as the front. They are cheap and plentiful, most are 4.10 or 3.73 geared many have Gov lock diffs which are much stronger than the infamous govbombs , later versions have better pinion seals. They have 1350 u joints but you will need to have your driveline shortened an inch. The breaks are similar and if you trade the wheel cylinders for the ones from your 12 bolt the original break lines will screw right in as well as the e break cables

[Mike C]

Good mention about driveline length. On a lifted truck the stock driveshaft with a conversion shaft should work.

On both trucks I have done this on, we redrilled the perch to move the axle back 1" which makes the wheel much better centered on the truck. Another feather in the cap for the SF 14.

[ManNamedJed]

I broke a 12 bolt in a 76 K10. I was doing a *bit* of a burnout though...

[El Dorado Jim]

Originally Posted by 1976gmc20

Just convert everything to Full Float and 8 lug wheels and then you can run real E-range truck tires

I've had nothing but trouble with 15" wheels and radial LT tires on half tons. The old 700-15 bias ply did hold up pretty good.

I agree go heavier and not worry about it!!