I've read on here that the half shafts are different on the '80 automatics versus the 4-speeds. I picked up this set up for my 1980 auto with the 4-speed 2:72 gears. Will I be able to use these half shafts with my auto pumpkin?

http://forums.corvetteforum.com/c3-p...om-1980-a.html

 

I think the only different between the auto and manual rear diffy's are the spindles. One set of spindles should replace the other. If you use an automatic rear with the smaller u-joints the half-shafts must match as well as the spindles on the trailing arms. You can use an automatic rear end setup with solid u-joints instead of the ones with grease fittings for a little extra strength. You can't mix and match otherwise.

 

So I would have to either change the gears in the new assembly or use my rear end and half shafts and change the spindles on the trailing arms?

 

Post photo's.

The issue is the straps that hold the U-joint caps onto the stub axles coming out of your differential...and also the straps that hold the U-joints to the inner bearing flanges...where the U-joints bolt to the inside of your trailing arm/bearing assembly area.

The cap/cup diameters are different. The manual differentials have much larger diameter bolts that hold the U-joints to the stub axles and the inner bearing flanges. Usually inverted Torx. AND ARE LARGER than the bolts that hold the drive-shaft to the differential. WHILE an automatic differential will have bolts that hold the U-joints at the stub axles and inner bearing flanges the SAME SIZE as the bolts that hold your drive-shaft U-joint to the differential.

SO...if your diameter of the U-joint caps of your new half shafts is different than what is on the car now...those are the parts that would need replacing. I myself would prefer to use the manual half shafts due to being larger.

You can get a combo U-joint...but usually those have grease fitting in them and that is somersetting I am not crazy about using. I use only solid Spicer U-joints.

DUB

 

I'm thinking the way to go may be to just have my gears put into the manual differential. That way I'll have the heavy duty axle stubs, half shafts and spindles. I'm sure my differential could use a refresh anyway. Make sense?

 

Here is the Deal. There are Two different U-Joint Sizes, Spicer 1330 are the weaker ones and 1350 are the stronger ones. The Straps that Hold them on use 1/4" Bolts for the 1330's and 5/16" for the 1350's. So just Check the Bolt size and You will know what You have.
To switch from one size to the other You need to switch the Yokes , the 1/2 shafts and the Axel Flanges, and of coarse the U-Joints. Everything is bolt on just switch every thing from one rear to the other, with maybe the Exception of the Yokes. If everything is brand new its no problem, except the used Yokes have wear factor, and now You are switching used worn parts for other worn parts. Start by sliding the Yokes in and out and try to determine how much play You have. There is a lot to be said about how much play is to much, it depends on what You use the car for. If all You do is drive on a trailer to go to the car show them who cares how much. If Your Road Racing and entering a Corner over 100 MPH then You better go by the book.
To remove the Yokes from the Pumpkin the Batwing needs to be removed and each Yoke has a Snap Ring. One needs a good set of Snap Ring Pylers and they are a bit difficult to do the first time around. If the Yokes are really worn they may be mushroomed out on the Ends. Nothing needs be done to the Carrier, just change the Yokes. Now that You have the New ( Used) Yokes measure the end Play again and see if its worse of better than the original. If its got to much Play for what You use the car for You have a couple of options. (1) buy new Yokes, there expensive and depending on who You talk to only one is still available. (2) buy aftermarket hard'd ones ( more exspensive) they may or may not be available, (3) Weld the end Of the Yoke and Grind until You have the end Clearance You want. This isn't really recommended but its been done many times, goes back to what You use the car for.
Keep in mind anytime You open up one of these rear ends You are opening up a can of worms and it may quikly escalate to a complete rebuild.

 

"Keep in mind anytime You open up one of these rear ends You are opening up a can of worms and it may quikly escalate to a complete rebuild."

Amen to that...