Question regarding GM 14 bolt axles

[BrianTN]

Hi, I was wondering if someone could point me towards some information about what type of rear end this is. It's in my family's 1998 Chevy K2500 work truck. I looked through the RPO codes and it has 3.73 gears, but I wanted to find some more in depth information because I'm curious about it and will soon change the gear lube. After a couple hours of searching I'm still not sure exactly what it is. All I know is that it's a 14 bolt. The only marking I've been able to find is 646. Is there a way to determine the ring gear size? Whether it's full or semi floating? Which cover gasket will I need once I change the oil? And then which oil should I use? Dino or synthetic, then with or without lubricant additive?

 

[locrwln]

Pretty standard Semi-Float 14 bolt, 9.5" ring gear (33 spline) rear GM axle of that era. Pretty solid axle that can take quite a bit of abuse.

Jack

 

[BrianTN]

How do you know it's 9.5" ring gear? I was reading some sites that say there are 10.5" also. Curious if one is stronger than the other.

 

[justcuz]

GM makes 2 14 bolts, one has a 9.5" ring gear like yours. The other is a full floater with a 10.5" ring gear. Any GM truck website like GM full size will have tons of info on these.
Or google GM semi float 14 bolt.
If it has a G80 code in the RPO codes on the inside of the glove box, then you need to add friction modifier to the gear oil.

 

[highdesertranger]

they are right. 14 bolt semi floater 9.5 ring gear. highdesertranger

 

[4x4junkie]

The 10.5" has a removable pinion support which yours does not have.

Like was said, the 9.5" is a great axle for what it is (far better/stronger than the 8.5" 10-bolt used in ½-tons, and is sought after by some of their owners). The 10.5" was made for heavier-duty service (is also used in 1-ton C/K-30 / 3500 trucks), it's a larger axle w/full-float hubs (also identifiable by the 8 axle bolts that attach the axle shafts to the wheel hubs)

 

[superbuickguy]

the advantage of the semi-float was you could get it in a 6 lug configuration.... other than that - the 14 bolt full floater is better in every way.

14 bolt full floater with G80 option




adding disk brakes to that rear differential - notice the fully-removeable axle shaft?



the truck it's under


1983 Chev 4x4 diesel, gale banks turbo, 700r4 transmission, 12,000 lb winch, air bags.... this is what I use to haul big stuff

 

[Smithy]

Yours is a 9.5" semi float.

A 10.5" with the removable pinion support looks like this:

 

[BrianTN]

Thanks for the input. I have a bunch of synthetic Lucas 75w90 oil. I'd imagine this would work. The manual calls for 80w90. I don't have the Eaton G80 so I don't need a friction modifier? I'll pick up a gasket like Felpro #RDS55387.