I'm removing the 4x4 C6 and replacing it with 4x4 ZF5. There is less than an inch different in the length of the trannies and there is more than enough adjustment in the mounts to make up the difference and that is no where near enough difference to need new drive shafts.
I have a US gear Underdrive unit between the T-case and the tranny. So I'll have an over and an underdrive. I had to modify the tranny tunnel pan from the ZF5 donor so my old school T-case shifter would pass through the pan (like they do on all '83-'86) as the donor '91's T-case shifter passes through the floor of the cab.
The rest will be changing the pedals out, moding the firewall for the clutch master cylinder and getting rid of the column shifter. The Tranny otherwise will bolt into position.
Heath
Just for the record, the zf driveshaft and the c6 driveshaft are different. They are different lengths, and the zf has larger u-joints and a heavier walled tube.
That's not to say that you can't make the c6 driveshaft work, apparently everyone else is, but I have a 89 f250 4x4/c6 and I bought a 89 f250 4x4/zf donor and installed the zf in place of the c6.
I compared everything off the donor to mine.
-The lower zf crossmember and rubber mount are the same.
-The short upper zf crossmember brackets are not the same, and the c6 ones will not fit when you use the rearward hole for the lower crossmember. The lower crossmember has slotted holes, but none of this worked for me, I had to move the lower crossmember to the rear holes in the frame, and use the zf upper brackets.
-The zf rear driveshaft is shorter. I used it. But when I went to put it in the rearend, the u-joint would not fit. I had to take the big nut loose on the donor rearend and swap the yoke onto my truck to make the zf driveshaft fit. The zf u-joint caps were bigger diameter, and it's very obvious the driveshaft is heavier than the c6 driveshaft.
-Unexplainable is the front driveshaft. They were the same length. I might have gotten into a previous owner thing here, but you would think it would be longer since the transfer case got moved back with the crossmember.
-The wiring is different. Look under the brake booster and there is a lime green plug. Unplug this and take this harness out, and plug the zf harness in, and it all works, no wiring hassles with neutral safety switches and reverse light switches.
- You have to have the manual clutch/brake pedal assembly
-It's nice to have the floor plate that already has the hole in it.
-There is already a hole for the clutch master cylinder, just pull the block off plate out.
-I didn't use the clutch electrical switch, but there is a harness for that to.
). You can probably find a good used ZF for MUCH less, and although I'm personally not a fan of it, you could also follow Mel's advice and do a Lucky mod and save yourself some $$ on that front as well.
