14 Bolt Full Floater in Short Bed 4x4... Driveshaft?

[Chris in Idaho]

I have a 1986 short bed 4x4 with SM465/NP208 and a buddy is making me a deal on a pair of axles: A 14bolt full floater and a 8 lug 10 bolt front. What else will I need to change to run these axles? My truck has stock 10 bolts right now. I assume the front will bolt right up with no problem, but what about the 14bolt? Will I need to shorten the driveshaft? What about U joints? What about brake lines? I haven't gotten the axles yet so I can't look at them. Anybody done this?

[Walts_restoration]

interesting. Bumping for the cause

[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.

[Chris in Idaho]

Great info, thanks!

[turbotank]

I am putting a 14bolt ff in my 89 suburban,I have learned alot from these fellows,maybe I might be able to help you if you need it.BTW,get your muscles ready,those axle nuts holding the u-bolts are a blankity-blank-blank

[turbotank]

I know this is an old posting,but hey,its taken me awhile with life going on right now. I am almost finished with my swap,and I have a question for anyone,or maybe larry in particular. I have swapped in my 10 bolt for a 14 bolt full floater rear on my 1989 suburban. I need to get the bastard joint to fit from my driveshaft to the rearend. Larry listed a part number for the earlier models,but will that work on the later suburbans? I.e. Did they change? Thanks. THe 14 bolt is off of an 85 c20.

[turbotank]

Meant to say that I put a 14 bolt in place of my 10 bolt!!!

[sdavid]

Should use the same u-joint. The larger ends are 1350 size and smaller are 1310 size if I remember correctly.

[turbotank]

I dunno,the drivshaft cap measures 1.125, and I am thinking the 1310 measures 1.064. I am thinking that this driveshaft has the 3r ends....

[turbotank]

I am thinking 3r for the smaller ends,possibility?