stuck on differential swap (3/4 ton diff from 79 K20 to 80 K10)

[bwendt1980]

truck 1: 80 K10, 400 sbc, sm 465 4 spd, Np 205 transfer case, long bed
truck 2: (donor) 79 K20 350 sbc, same trans and xfer case.

Ok, I have managed to remove the diff from both trucks, and get the 3/4 ton diff under the K10. I did all of this with no torches, no air hammer, and no shop. I did it in my back yard with 2 bottle jacks, a transmission jack, a floor jack and a LOT of cinder blocks. Now my issue is the drive shaft. Both shafts are good, but the one from the K20 is 2 piece and the one from the K10 is one piece. I can't use the 1 piece on the K10 now because the ujoint is smaller than the part it bolts to on the diff. (I think it is called the yolk?) I have already spent too much on this project because I have had to buy several tools, so I can't afford to have the drive shaft re-done. I decided to use the two piece,  but the crossmember that the carrier between the two pieces bolts to is not present on the K10. I have started removing the crossmember from the k20, but for the life of me I cannot get the rivets out of the frame. I grinded off one side and pounded and pounded and pounded on them with a punch. I got one to move about 1/16 of an inch. I grinded them flat with the frame, but they just don't want to punch out! I have already removed the bolts from the cab and jacked it up so that it is not resting on the crossmember. I also thought about swapping the yoke from the K10 diff to the 3/4, but from what I understand, if that is not done properly, the backlash on the pinion won't be set right and it will destroy the differential. (I am only doing this because the K10 diff was destroyed) Any ideas???

[Jason S]

Use the K-10 driveshaft with a combination U-joint. The driveshaft side of the U-joint will match your K-10 driveshaft, the axle side of U-joint will match the K-20.

[Irish_Alley]

you can only swap drive-shafts if its from the same trans and same bed length. you can make a crossmember for the carrier bearing and get a new bearing unit then be done if all is the same. other wise you can go to NAPA (not autozone and advance have lost the paper books) cause there is no computer that i know of that will tell you what you need. but go to NAPA tell them what part you need they will look it up in the paper book then you have the right u-joint. but make sure your dive shaft isnt too long. if the 3/4 differential snout is longer than your 1/2 it will make the shaft too long and you might bind

[Blazin]

Cross over U joint is your best bet. As stated go to an auto parts store that has books, and can look up the two U joints for both trucks, Then they can cross those numbers to a joint that has both size caps, and cross.
It can be done on a computer but most of the dubs that run them don't have a clue, and will screw it up. If you can get your hands on a U joint book you could look them up, then figure out the crossed part number. Then you might have a chance at a chain parts store. thats if they are willing to look it up that way. I have just recently been getting my local Auto Zone trained to look stuff up by P/N instead of application.
Its called a Yoke.

[bwendt1980]

Great info guys. Both trucks do have the same bed length. I will try napa tomorrow. I spent a few hours getting the stupid rivits out of the crossmember just to kick myself really hard for not realizing that I cannot slide that cross member out because it goes from inside frame rail to inside frame rail. I might be able to slide it back further where the frame rail is taller then bring one side up and the other down, but I think my better bet would be the napa idea. Completely on target with autozone, one guy said that I would have to find a '$#*() joint' and I think he would have been able to find something, but he had to go to lunch and the other guy just looked up the two joints then was totally lost.

[bwendt1980]

on the plus side, I did learn a LOT on this project about fully checking things first. the only thing I was initially worried about was if the leaf springs would swap, and I just thought I could swap the caps on the u-joint. I have also learned a lot of work-arounds to not having a shop, and it gave me a great excuse to buy a lot of tools I have wanted for a long time. My next project is swapping the front axle so that I can use 4WD again. (currently the gear ratios are different and so are the tire sizes) I also want to double stick the NP 205 so I can put the rear in low without engaging the front, and put the rear in neutral with the front engaged. Any suggestions on those projects?