If it's an "open" differential, it won't be a G80.Well I found a rear axle - "1997 GM 14 bolt complete six lug axle with 3.42 gears and open diff" that a guy is selling local for $200 Its already off the truck but unsure of which model it came from. I'm guessing is a GU6 rpo code and most likely G80 too. He did say it was a 4x2 work truck so I'm thinking the width should be the same as mine [1996 C1500 silverado]
Any suggestions?
Make sure you can loosen the axle fill plug!
If it's from a 2WD pickup, it should be a direct bolt-in for yours, except for needing the conversion U-joint, and maybe polishing some rust off the yoke where it slides into the trans tailhousing. The driveshaft will poke into the tailhousing just a little deeper than with the 10-bolt.
Install new/working park brake cables into the struts and backing plates. Seems to me the cables are the same for 10-bolt and 14-bolt 6-lug axles, so whichever cables are in the best condition are the ones you use--or buy new ones.
I would pop the cover off, verify gear ratio. Should be stamped into the OD of the ring gear--the number of pinion teeth and the number of ring gear teeth. This photo shows a similar 9.5" ring gear with "11 (pinion teeth) 41 (ring gear teeth) " = 41 / 11 = 3.73 gear ratio
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Verify the brake hydraulic tubing and brake hose is good, pull the drums and inspect the brakes. Repair as needed. Get the regular (service) brakes adjusted FIRST, then adjust the park brake after the axle is installed. When it was me, I pulled the axle shafts out, verified the bearing surfaces on the axle shafts, and smacked new grease seals into the housing. Then fresh grease in the rear end, a gasket for the cover as required, and tighten the bolts. There's going to be some sort of axle vent; on the 4WD it's at the end of a hose that's bolted to the box or frame-rail. I don't know if the 2WD have that hose, or if the vent is right on the axle housing. Make sure the vent is clear.
If you intend to cram some sort of "posi" or "locker" differential case into that axle, now is the time, since you've got the cover off and the axle shafts out anyway. Don't disturb the pinion gear, (unless absolutely necessary) re-use the ring gear AFTER CHECKING BACKLASH BEFORE DISASSEMBLY. Put the thing together with proper bearing preload, and the exact same backlash. If you dick with the pinion, things get way more complex.
Then shove the whole works under the truck, clamp it to the springs with fresh U-bolts, torque to spec.
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