72 gmc rear end swap

[WATSON403]

I have a 72 gm half ton with an open diff and I'm sick of peg leg burnouts so I want a posi I also have 3.73 gears right now but I want a little more umph I could live with 4.10s but I would rather have something in between anyway Im wondering if you guys know what rear end outta what pickup would be compatible with as little to no fab

[k29349]

Why not just put a Detroit True-trac diff in your current rear axle?

[WATSON403]

I've never messed around with the gears in a diff so doing it myself I just figured it would be easier swapping axles instead of messing with gears and setting backlash

[k29349]

Ring gear back lash is pretty simple. The pinion depth is where it gets complicated. You would not have to mess with pinion depth. I put a True-trac in my blazer and the back lash stayed the same. It didn't even need adjusted. Watch a few vids on setting backlash and see what you think. I think the True-trac is better than GM factory posi anyway. No clutches to wear out. No need for additives. And probably a stronger unit also.

[cla511]

I put an Auburn in mine the other day and it rolled right in. Didn't have to change the shims or anything. To me the Auburn is a lot more drivable. A lot less hopping and popping in turns and parking lots. I did keep my old ring gear so that does make it easier.

[Mike C]

If you want to find a built rear that meets your criteria it will be (1) expensive if you have to buy it from a builder or (2) a long wait to find exactly what you want used.

The TruTrac is a great choice for a street vehicle as well as the Eaton posi (which is an updated, stronger version of the original posi) or the Yukon DuraGrip which is pretty much a copy of the Eaton.

If you are at all a DIY kind of guy with good mechanical skills you can do a diff swap because you are not messing with the pinion depth.

Get a mag base and dial indicator from Enco. Probably cost $50. Get a deluxe carrier shim kit (interlocking side shims they are MUCH easier to install) and order a posi. I would try someone like Randy's R&P and see if they would install new carrier bearings for you on whatever diff you choose. New ring gear bolts and gasket should be in your cart too.

Measure back lash on ring gear then pull diff apart. Put ring gear on new diff. Put shim packs together duplicating factory setup and reassemble. Measure backlash. Adjust by rearranging shims until it is same as you took it apart.

I could explain in detail, but there are 100's of writeups on the internet about installation that can give you that. Just hit the Google and feel good about ding the job yourself.

[terry b]

I THOUGHT HE SAID HE WANTED TO CHANGE THE GEAR SET? That would be the ring and pinon no?

[k29349]

Your not going to find a half ton rear end with something between 3.73 and 4.10.

[Mike C]

He said he could live with it but didn't specify he had to have it. It's certainly not worth the expense for a 10% increase in gear ratio.

[Ironangel]

Cost will depend greatly on what rear is under the truck...72 GMC's had either Dana 60 or GM 12T...? http://www.ringpinion.com/DiffWizard.aspx

[Z10]

Try a Richmond Powertrax. I have one in my 69 Camaro and about to put one in my 72 GMC.

Watch the video. Picture is worth a thousand words.

https://www.youtube.com/watch?v=8k-LmnS3ED0

[mechanicalman]

Originally Posted by WATSON403

I have a 72 gm half ton with an open diff and I'm sick of peg leg burnouts so I want a posi I also have 3.73 gears right now but I want a little more umph I could live with 4.10s but I would rather have something in between anyway Im wondering if you guys know what rear end outta what pickup would be compatible with as little to no fab

If it's a half ton, it's probably a 12 bolt. If it's a GMC, it's probably a leaf spring.

Assuming all this is true.....

Any chevy/gmc 1/2 ton pickup with leaf springs where the spring pads measure out the same on the tubes and same width drum to drum, should work as long as it's a five on five, and if the u-joint size turns out to be different adapter u-joints are available.

But as previously stated, I also think a true trac would be the way I would go and keep the 3.73's. Consider that you would NOT have to pull the pinion gear out and could likely use the existing shims on the new posi carrier with new side bearings.

[70blackfish]

take it to a rearend shop and have them install a posi, you might need a few bearing also like i did. if you have 3.73 don't mess with the ratio. just ad a posi.