I just installed a 12 bolt rear in my 85 K10 and go to bolt up the driveshaft and the yolk on this rear is smaller than the one for my 10 bolt. What should I do? Can I pull the yolk off of my 10 bolt and put it on the 12 bolt? Also when I remove the yolk I don't have to do anything special do I? I'v never pulled one off before, I would assume I can just take the big nut off and it just comes off? And I swap it with another one? I have to have this done by the end of tomorrow and I still have to swap the front end, I hope it doesn't have the same problem, but the front end is also a 10 bolt and so is the original so I suspect they will be the same just with different gears.

Measure the diameter of the orig u-joint caps and the width across it, then measure the width and diameter that you need for the rear end, in the back of the U-joint catalogs there are "Adapter joints" that have the correct specs for each side. GM used to use these on some of the muscle cars back in the seventies to mate 12 bolts to big driveshaft 400 turbos.

Thats what the guys on over on a chevy truck forum told me. One fellow is going to get the part number of the exact one that I need, I did measure the dimensions though anyway. Thanks... maybe i'll get this thing rolling again by the end of tomorrow

go to a napa and tell them you want a conversion u-joint. I think the napa number is 349 not sure but if the parts guy is any good he will know.

I just did the same thing to my 84 k5 blazer. Like I said most parts house (read not autozone, checker etc) will be able to help. Oh and they are not cheap around $26.00

I can handle 26 bucks, since i'm sure as hell not putting that 10 bolt back in, all I gotta do is bolt up my driveshaft, so thats not a good option to put the old one back in now lol. I'd rather pay the 26 bucks than do swap them again.

Found the right U-Joint at carquest, took me and the counter guy to find the right one, he had to call up someone to help find the right one. He said he has never sold one of those U-Joints in his 20 years working there. And it was right about 26.

When I put a 12 bolt replacing the 10 bolt in my suburban I noticed that it sat out of the transfercase a small amount more than before. I suppose the yoke set up puts the center of the universal slightly further back than the 10 bolt. I also used the cross over u-joint.