72 gmc DANA60 to 14 SWAP easy or not?

[erikgto]

Hi Guys,

Because I'm not very fond of doing 4.000 rpm @ 70 mph I'm looking at my options and one of them is replacing my 4.56 Dana 60 with a 14 bolt corporate 8 lug axle with 3.73 or higher gears.
However, I don't know if the 14 bolt is an easy or difficult swap...

Are the spring perches located in the same spot or do I need to remove and reweld my springperches/pads on the 14 bolt in order to use them on my 72 GMC 2500.
Also, can I use my driveshaft in it's current length or do I need to shorten or lengthen it?
Any other issues I need to be aware of?!?

Any advice on this would be greatly appreciated!

[erikgto]

No did this before me?

There must be someone with some knowledge on both Dana 60 and 14 bolt rear axles?

Please chime in..

[SS Tim]

Are you sure its a 4.56? IIRC Chevy didn't offer the 4.56 gears with a 350/TH350/Dana 5500. Thinking 4.10 was the only ratio in fact. Might try a calculator and see if you gears and speedo are correct first before doing any changes.
http://www.summitracing.com/expertad...tio-calculator

As far as ratios go changing the gears would seem to be the better solution in your case. Dana 60s have a wide selection of gear choices but there would be a case change in all probablity if you go a lot higher.

Then there is the question if you are using the truck as a truck or a car and don't need the towing/load hauling ability low gears provide. For the best of both worlds an overdrive (auxiliary transmission) might be the best choice.

[erikgto]

It is a 1972 GMC 2500 350/350 Dana 60 rear truck.
No gear options on the spid which should lead to a factory 4.11 rear gear.

The rpm's the truck turns on the freeway do not go with the 4.11 gear.
I hooked up another tach thinking the factory tach might be way off reading too high, but the second one reads about the same rpm's.
According to the online rpm calculators using the trucks tire diameter; they give a rear gear close to 4.56.
Don't know if GMC ever sold those, but I think they did. Especially on manual shift trucks.

Thought about a 200-4r trans, but I might use it as a tow vehicle if the need arrises. I'm afraid the trans won't hold up towing a heavy trailer...
That's why I was thinking about a 14 bolt swap.

I briefly thought about a 5 lug axle swap and bought a stock 1979 Blazer 2 wd chassis, but thinking about it a 2.7x gear axle might not be able to pull anything in a halfway decent manner.

Erik

[nra4life]

My '72 has a 14 bolt corporate rear end in it. The rear end is from a 1990 1 ton Chevy pick up. It is a 4.10. We used it to make a bullet proof 5th wheel tow vehicle. It is not a difficult swap. There are a couple of goofy things on the axle housing to deal with. On mine, both backing plates are identical - not mirror images. The right side e brake cable comes out to the rear and loops a 180 and goes along side of the left cable along the left frame rail. It looks odd, but not hard to adapt to the '72 cable. I bought after market spring pads and welded them in the appropriate places. The wheels are in the correct locations. I gained 13 x 3 1/2" drum brakes with the swap. If I remember correctly, the shock mounts were ok. You will have to deal with the brake pressure valve on the axle housing - remove it or make a bracket so it will work. Another thing you could do is find a big block with automatic transmission. The 3/4 ton models have a 3.54 gear in them. That's what mine had originally. To compensate for the lower gear, we put in a Gear Vendors unit. I hope my ramblings are of some help. Roy

[Mike C]

Your truck should have 42.5" spring centers, same as a '73-87 3/4 ton. But the shock mounts will have to be relocated. Easiest bolt in option would be for a 3.54 geared Dana 60 from a big block 67-72 truck.

A built TH200 4R is a good trans, but you have to spend $$$ to get there. Performance all around would be better with the Th200 and is what I would consider. A beefed up 200 would run you about $2000 installed with a new converter. A good rear axle rebuild would probably be $600 with parts, maybe more.

Which takes you back to the 3.54 60 price wise. They aren't that uncommon and they aren't desirable for the hop up guys for the most part.

[71K20chevy]

Just got done with a 14 bolt swap, unless you get one from a 1 ton truck the spring perches will have to be moved.