6 to 8 lug axle swap

[bhayes1]

Bought a K20 with a bad 4.11 rear diff. It got me thinking. If I have a set of 6lug 3.73 1/2 ton front and rear axles in good condition, could I swap out the 8 lug shafts into the half ton set up. So basically I’d be running the half ton set up but be able to keep my 8 lug appearance on my k20. Personally I’d prefer the 3.73 ratio anyways. How intrusive of a swap would this be?

[kwmech]

On the 69? axles are not even close unless there has been previous swapping going on. Need more info or pics

[bhayes1]

The truck is a 1971 K20.

It has a bad rear diff. I have access to a square body k5 with 3.73s and wanted to see if I could make that work but it sounds like the rear axle splines won’t allow me to convert the k5 rear end to 8 lug since my current rear end is bad.

Most likely I will keep it 4.11 gearing. Most threads show that axles out of 73-87 trucks will work if I widen the spring perches. I just got a hold of a guy with an 89 3/4t burb that has the 4.11s. Can someone Confirm this rear end will fit my k20 if I move the perches? Again this suburban is an 89 (outside the 73-87) range.

[Mike C]

The '89 burb axle will work. I have an 86 sub axle in my Jimmy. But the 89 MIGHT have 14mm lug studs instead of 9/16. It will also be the semi-float 14 bolt and not the full float but it's plenty stout enough.

[57taskforce]

I’d swap a 14 bolt full floater in personally. The semi 14 is strong but the Full floater is king of the hill in my book. A srw 1 ton 4x4 square body rear will bolt right in with the exception of one shock mount. Perches aren’t a big deal if you’ve got a torch and a welder.

[bhayes1]

That would be nice if I could get one easily. Looks like I have found a Dana 60 w/4:11 gears and a posi out of an old forest service truck. It’s cheap and within driving distance. Any thoughts on that? Oh and it’s out of a 69 I believe so the perches and shock mounts should line up?

[bhayes1]

Or is it worth it to wait on the correct 14 bolt just simply due to parts availability?

[weim55]

Why not repair the original in the truck now?

Steve weim55 Colorado

[bhayes1]

Welllll from what I’ve read it is beyond my skill level. Anytime dial indicators, shims, working in thousandths, preload, etc. come into play I’d rather not dive into that. I’m sure I could figure it out but at what cost. Seems like bolting in a working one is simpler. In addition, the previous owner worked on the rear end prior to getting the truck so who knows what was done right or wrong.

[57taskforce]

If that Dana 60 is out of a K20 id use it if it’s in good condition. If it’s out of a 2 wheel drive truck your still going to have to move/replace perches and shock mounts. They aren’t quite as strong as the 14 bolt but still plenty stout. As far as I’m aware you can still get parts for the older rear 60’s.

[bhayes1]

Ya pretty sure it is out it’s 4wd. It also comes with a front d44 both for $200 and a couple hour drive. Guy said he pulled them from a running truck he was going to use for a build then decided to put a modern chasis under it. Not that I need it but the 44 also has hydro assist steering (my front is still good) but figure I might be able to recoup $100 bucks if I sell it... or just keep it around as a spare.

[weim55]

Likely the original diff in your truck is an HO52. The center section will drop out of the housing as a complete unit. Shouldn't be too difficult to find a complete used center section in the ratio you desire. Bolt in and go, certainly the cheapest and easiest solution if the rest of the axle unit is OK.

Steve weim55 Colorado

[Mike C]

The Dana 60 and the semi-float 14 bolt are both rated at 5500# GAW. If you have the one cheap, I would run that and start working and quit looking.

Most likely your GMC truck has a Dana 60 in it as that was the norm but there are exceptions.