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Axle swap compatibility/

7

78 GMC Jimmy

1/2 ton status
Joined
Jan 30, 2024
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Location
Seattle, WA
Trying to get an 8 lug posi rear axle. My 78 K5 8 lug left axle seal is bad and the yoke seal is bed. Found an axle for $100, but will it fit?


Info from seller:

Came out of a 1963 gmc 3/4 ton truck

I replaced it with a full floating 14 bolt and the perches were the same because my truck was a 2 wheel drive.

Wms to wms is about 65 1/2”. Center of leaf spring perch to perch is 42 1/2.

I’m not going to open it but they both spin the same way and the tag says 4.10

Link: https://seattle.craigslist.org/sno/wan/d/seattle-lug-posi-k5-blazer-axle-wanted/7761041876.html


00U0U_4xoh0uGRe9k_0fu0bC_600x450.jpg



Have to weld on new shock mounts I think.

Thanks for any input you may have.
 
Last edited:
78 GMC Jimmy said:
Due to durability, or? Any main advantages to a 14?
Click to expand...


Im not opposed to rebuilding mine, and installing a posi - but I have never done it before. I don't have any special tools that may be needed, or anything like that. Plus the posi would be super expensive I bet. And a local shop would be ridiculously expensive - in the range of $2500- $3500.
 
Wouldn’t a 63 GM be the old cooperate axle? Eaton HOS62 or whatever they were called? A Dana 60 from 63 would like have 16 spline axles….agree to hold out for a 14b, plenty of availability, strong aftermarket support, and if it’s a 3/4 ton it’ll bolt right in
 
Chickntrk said:
Wouldn’t a 63 GM be the old cooperate axle? Eaton HOS62 or whatever they were called? A Dana 60 from 63 would like have 16 spline axles….agree to hold out for a 14b, plenty of availability, strong aftermarket support, and if it’s a 3/4 ton it’ll bolt right in
Click to expand...

That's two strikes against the axle that I was looking at (so far).

He wants $100 for it, or $150 total delivered to my doorstep.

Pass, or buy even if i don't use it? Is it a good value for resale or a spare?
 
I dunno how strong the G80 in a semi float is. Full floater is decent, I’d still hold out for a full floater myself but the semi float van axle is better than the 1963 axle
 
78 GMC Jimmy said:
How about this one:

$125

G80 gov-loc

8-lug 14 Bolt G30 VanRear Axle​

4.10 gear ratio, semi-float rear axle pulled from a 1992 G30 van. This can be used to match the rear track width to the front on a Squarebody Chevy.

New pics: (look at the ones with the truck frame in the back ground.)

Click to expand...
If you haven't noticed, that van axle is also my ad and I talked to you for a bit yesterday. From what I can tell talking with you, you already have a 14FF in the K5. Fixing your oil leaks and dropping in a lunchbox locker will be cheaper than buying my 14 bolt and doing the brakes and seals. Then you wouldn't need to worry about figuring out gear ratios.

This is probably the cheapest option on the market I have seen:

But, before you order anything, you want to be 100% sure of which axle you have. The 14SF is the GM 9.5 and the 14FF is the GM 10.5.
1719592428541.png
 
kennyw said:
If you haven't noticed, that van axle is also my ad and I talked to you for a bit yesterday. From what I can tell talking with you, you already have a 14FF in the K5. Fixing your oil leaks and dropping in a lunchbox locker will be cheaper than buying my 14 bolt and doing the brakes and seals. Then you wouldn't need to worry about figuring out gear ratios.

This is probably the cheapest option on the market I have seen:

But, before you order anything, you want to be 100% sure of which axle you have. The 14SF is the GM 9.5 and the 14FF is the GM 10.5.
View attachment 479883
Click to expand...
He’s got a 14FF - we’ve discussed this with him on other threads.
 
OK, I can see the listing but I can not post anything on that page.
kennyw said:
He called it a SF and sent me a pic of a FF cover on messenger. So, I wanted to double check.
Click to expand...



Swapping out the diff looks like a lot of work. It just seems like it would be easier to swap the axle.
 
The 14bff is one of the easiest axles to work on, and you’re not setting anything up if you install the locker shown. It’s what’s called a lunchbox locker and drops into your open carrier. Why swap in a weaker axle that needs more work?
 
Doing a lock-right is easier than an axle swap. You just take off the diff cover, pull the axle shafts back (unbolt at the ends), take the spider gears out, assemble the locker parts inside the carrier and re-assemble. No gear setup. (unless you have really low gear ratio or thick gears or something unusual).

1719605456246.png

However, you have to be sure what you have now is an open carrier and not a G80, Detroit, or anything else. They only install in the open ones.

The axle swap requires new U-bolts, bleeding the brakes, maybe replacing brake lines or wheel cylinders when stuff breaks and a lot of hauling stuff around (get the new axle, get rid of the old one, storage, etc.). Also, if the new axle has significantly different brakes you may need a proportioning valve or different master cylinder (although that's easy to avoid with another 14BFF). That's assuming it's an axle from a 3/4-ton Chevy. If not, add in moving shock mounts and spring perches.

But first, is a locker what you want? Have you researched limited slips, tru-trac, detroit, G80, etc. to know the pros and cons? What are you trying to accomplish?
 
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