[DirtyLarry]

Yes, you will need to shorten the rear driveshaft as the pinion on the 14 FF is much longer. You can have a driveline shop built you a shaft one of a couple ways. Either shorten your existing drive shaft and use a bastard U-joint that will have small cups on the drive shaft end and large cups on the axle yoke end as the 14 FF uses much larger U-joints than the half-ton axle. That is what I have been running on the 14 ff in my ’78 K10 for over 10 years and never had a problem. The Napa bastard U-joint part number is 240-0358 to mate a ’75 14 FF to a ’78 half-ton shaft.

The other options would be to have the driveshaft shop build you a larger diameter driveshaft tube with a larger end yoke on the shaft so the rear U-joint cups will be the same size on all 4 cups OR have the shaft from the truck where the 14 FF came from shortened if you have it. If you go the route of building a new large tube shaft from scratch, sometimes there is an issue with the drive line shops finding a shaft yoke end at the front of the shaft for the larger diameter tube to that is of the size to match the joint for the slip yoke for the transfercase. This route gets pretty expensive. Shortening a shaft is much cheaper than lengthening or creating a new one for that matter.

I don’t recall any issues at all with hooking up the brake lines but you may have to do some fabrication to connect the park brake cables. Mine is a ’78 with a ’75 rear 14 FF so there were no issue with the park brake cables. I believe 1986 have the park brake cables running down one side of the frame rather than one cable running down each side. That could be an issue. I ran into that when swapping in a 14 FF in a 1988 Suburban a while back.

Don’t forget about new U-bolts…. The rear 10 bolt U-bolts will be too small for the 14 FF axle tubes.