88-98 C/K 14 bolt full float rearend swap?

[Jason S]

I've seen postings and researched myself about the 88 up semi-float 14 bolt 6 lug but nothing about the full-floater 8 lug.

Has anyone on here swapped one of these in to a 73-up truck?  I understand they are a bit wider and spring perches and shock attachments would have to be moved, but are there any downsides that I may be missing?

As far as the pro's: they are newer and may be less likely to need a rebuild, cost of a complete axle assembly would be less than parts to completely rebuild a 70's 14-bolt, removable brake drum, wider so more stable (that may be a stretch). 

Without having done much research, the only cons I see are the aforementioned cutting and welding of the spring/shock locations, possible issues with the E-brake connections, metric threads on the wheel studs and maybe metric hydraulic brake lines (?), compatibility with factory proportioning valve (?). 

If it really comes down to cutting spring & shock mounts and welding to use the 88-98 axle versus the several hundred dollars for bearings, ring and pinion, plus the time to setup gears on the '73; I'm thinking the later rear end comes out shining.

[Engineer]

There were several changes done on the 10.5" 14-bolt FF after 1988. Not just an axle housing change to fit the GMT-400 trucks.

Other than the normal options, the 73-87(91) 14-bolt stayed the same.

Unless the axle in question was abused,(no oil, water intrusion, mud truck, etc.) these things seldom wear out. I would stick to the 73-87 axle for simplicity.

If you really want to build the ultimate 14-bolt FF look for a late model axle with the finned cast center housing. These had a larger inner pinion cone bearing, and thus a higher torque capacity. They also came with 1410 u-joints in the heavier applications.

Cool thing is through all of the changes over the years, all 14-bolts still use the same ring/pinions, and differentials.

[Jason S]

At this point I'm just doing some head scratching and trying to put together a game plan.  It will ultimately depend on what is available when I decide to pull the trigger and finally redo the rear end. 

[bake74]

     JasonS, you are right, the biggest obstacle you will have is the E-brakes.  But if you are capable to re-weld spring perches and shock mounts, I would assume you could also fabricate a system for the E-brake cable.
     Both opinions are valued.  The newer rear ends have more ratio options, only problem is if you are planning on swapping in a k10 and changing gear ratio's, you might not be able to match the fronts to the rear. ( 73 -87 axles are limited to a few ratios ).
     

[Jason S]

Thanks Bake and Engineer.

I'd be looking at keeping the current 4.09 Dana 44 front or possibly swapping a 3.73 Dana 44 front.  I don't think either gear ratios should be too difficult to find on the later model rear end. 

Mainly, I'd feel much better if I could skirt around pulling apart a rear end by cutting/welding and a little modification. I'd think that it may cost less to adapt the 88 up 14 bolt versus a complete rebuild a 73-up 14 bolt. I may or may not save much money or time by using the later rearend.  Again, any suggestions, advice or other information would be greatly appreciated. 

I have a spare set of D44/14B FF axles in 3.73.  SO, using those may be an option; however, I still have to check them out. 

Here's why I'm trying to gather information...

As most of the mechanical work I did on the '73 GMC K2500 is going on 13 plus years and >120,000 miles. Even with overall very good maintenance, I know I'm going to have to start rebuilding and replacing parts.  Because of the 4.10 gears, most of the miles on the engine and transmission have been at 3,000 rpm...

A)The GM crate 350 has been outstanding, but it's starting to use oil and now I have to put a new front seal on it. However, valve stem seals and possibly a valve job are still probably in order. 

B) The front Dana 44 internals are good, the rest is a bit loose. So ball joints, tie rods, etc. I recently repacked the bearing and noted that those will probably need to be replaced in the near future.

C) I've never rebuilt the rearend (14-bolt FF, 4.10) on the truck.  I know it will need bearings, if not a ring and pinion.

D) I've wanted to swap the NP203 for a NP205 with either an auto overdrive or a 4-speed manual.

E) There is some rust beginning to show up on the cab and behind the rear wheels.

SO, I think at this time that I'd prefer to do a complete tear down and rebuild of the truck versus the driving rebuild. The main thing I'm waiting on is whether I'll be transferred (by my employer) in the near future.  I'm not keen on the idea of pulling everything apart and then be told you'll have to move!

In the meantime, I want to have a game plan together so when I do decide to pull the trigger I am actually spending my time working and building and not researching, searching, etc. 

For the remainder of the drivetrain, my current line of thinking is build a 383.  If I keep the 4.10 ratio, then use a 700R4 auto.  If I use a 3.73 ratio, then go with the 4-speed or 700R4. Engine and transmission are still in the air, although I really like 4 speeds. 

I've been very impressed with the information on this site and how helpful everyone has been and appreciate honest input.