84' k10 3/4 ton axle swap

[jaydee6634]

Just picked up a pair of 84' 3/4 ton axles to swap in to my 84 k10. the axles are 10 bolt front and 14 bolt full float rear. Both axles are 3.73 gears. Currently I have a 10 bolt front and 12 bolt rear with 3.08 gears and 31" tires.

I plan to "Rebuild" the 3/4t axles and by rebuild I mean just new hub bearings and seals etc. and disc brake conversion on the 14 bolt. And add 35" tires.

I currently have a goodwrench crate 350 pushing about 250hp mated to 700r4 and np208 tcase. Truck is my daily driver with very limited wheelin and the occasional heavy loaded bed, you know using a truck as a truck.

I am wondering if anybody has some tips/tricks/advice for completing this swap.

I believe from the research I have done that the front drive shaft should work but the rear will probably need shortened.

Do I need to change gear ratios?

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[Dutch Rutter]

I cant say anything about the axle swap so someone else will need to chime in about that.
But as far as gear ratio, In my DD 83 k20 I have the same setup except with 4:10-ish ( I have not yet verified this by taking the cover off) and 33s and I feel that is about as big of a tire I would go without re-gearing. Again just my thoughts.

 

[bucket]

Should be ok with 31's. 33's or larger can work with 3.73, but OD will be useless 95% of the time.

 

[4WDKC]

35s with 373s will be like 1500 rpm at 70, it sounds ok in prcatice but in reality the trans has to down shift for even the slightest hils. 456s with 35s is a better option but hard to findm 410s is supposedly the ideal gear for 33s with od

 

[Craig 85]

I did an axle swap on my last truck, '79 K15. I used axles from an '82 with a 14 bolt semi-float rear. The front shaft bolted right in. I did have to shorten the rear driveshaft. My truck had a fully smogged 350 with a TH-350, so I'm guessing it had 150 HP. I went from 3.08's to 4.10's. I definitely picked up some power on the bottom end, but I was turning about 3000 RPM at 70 MPH with 33's. With 35's and 3.73's you may not be in OD too often.

I used this hybrid U-joint at the rear axle. Spicer 1310-1350 # 5-460X or O’Reilly’s – Precision U-joint # 348
(3.219 / 1.062 to 3.625 / 1.188). Use a master cylinder for an '84 K20 with JB7 or JD7, 13" rear brakes. If you notice in the second picture, my M/C reservoirs are reversed between the 1/2 and 3/4 tons. In this picture you'll see the rear brake reservoir is in the front on a 3/4 ton M/C. I just had to swap the lines. I don't know if it is the same on your year.

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[Frankenchevy]

I have 3.73 with 33s. Pretty good combo with a th400. I’m talking from my paper ass here, but I’d go with 33s or get 4.10s if your set on 35s.

 

[dougbert]

I have a 1984 K10 with a 5.3L silverado engine in it

I am swapping to 14bolt FF rear. In my build thread I start that discussion at

http://www.gmsquarebody.com/threads...in-with-a-2002-5-3l.14428/page-35#post-363704

then over several pages have info on the new diff mingled with other tasks

both my current front 10 bolt and rear 12 bolt are 3.08. I currently do not have a front drive line. My 14bff is 4.10. I have a new 4.10 ring and pinion along with new seals and bears to overhaul the front 10 bolt. I will also be taking the front 8 lug spindles from the 14bff donor vehicles so I will be 8 lugs all around. I discuss ,my 14bff conversion to 1 ton disc brakes as well. Then after the new 14bff is installed, I will order a new 4" Aluminum driveline with 1350 ujoints for strength.

hope that helps some

dougbert