G80 Rear End 1996 K1500

hibrad2005 · December 28, 2007

OK, here goes, this is kinda a long and complex issue. OK, so I have a 1996 K1500 With a 350 V8, auto trans, and a G80 rear Differential, 3.73 Ratio, about 165K miles. My problem is that when I put the truck in reverse, It kicks really hard, so hard the bed jiggles, and on rare occasions (5 times in the month I have owned it) it makes a horiffic grinding noise, like someone that doesnt know how to shift a manual. Now, It doesnt kick first thing after sitting for 8+ hours (cold fluid) But it does any other time, Also, it has absolutely NO problems at all in Forward gears. I know its in the rear-end, because when it pulls its grinding stunt, the driveline is spinning (verified by someone outside the vehicle while it was doing and they were looking underneath) Secondly, the RPM and speedo go up rapidly when its doing this grinding. (at which point I have to put it in neutral, wait for the RPM to go to idle and the speedo to go to 0, then put it in reverse, and it will just kick hard, like "normal")

A mechanic told me that he thought the spider gears had missing teeth, but I asked, why would reverse, when warm be the only time this happens. They recommended a rearend rebuild for $1000, not only am I poor, but that sucks for a vehicle I havent had for more than a month, and since theres no lemon law here Im stuck with it. I havent opened the diff yet to inspect it, its been too cold and I dont have a lift, and id rather not do it while its on the ground, kinda cramped. I have a mechanic friend who can take a look after the 3rd of January, and Im sure ill be ok till then, but Im at a loss, no-one seems to know what this gremlin is. Reverse only hell! AHHH! OH and as a side note, the U-joints have no noticeable play. So they check out. Im afraid something is going to break though and Ill be stuck, so Ideas? Please?!?

skills4lou · December 28, 2007

Sounds like you really need to open the diff and take a look. When you put it in reverse, is the driveshaft spinning, but the truck doesnt' move? If that's the case then you definitely need something in there replaced. $1000 is insane though. Just get an axle from a junkyard and swap 'em out. That's a very common axle, so it shouldn't be hard to find a replacement.

hibrad2005 · December 28, 2007

Axle, I called all my local Junk Yards, and they have 1, from a 98, and they want $500 for it, with an exchange, my problem is, I dont have the tools or the know how to get it swapped and the mechanics I talked to want $450 to do a swap, so that puts me d**n near close to the rebuild. I think I'm being screwed here.... thoughts?

srlbotanical · December 28, 2007

I would stop by your local Napa and pick up a new differential gasket and 3 quarts of gear oil. Pull the cover and check everything out.

Is the noise coming from the rear end or from right under the truck?

skills4lou · December 28, 2007

I agree you need to get eyes on the problem to confirm what's going on first. Is the junkyard axle a rebuilt unit? Why do they need your old one?

As for the actual swap, the hardest part is just getting the U-bolts off. If you have a basic set of tools, a decent jack and an impact wrench you should be able to do the swap. Throw in a buddy and a six-pack and you'll be done in a few hours tops.

After you get the cover off and confirm any carnage, measure the distance between the spring mounts and the full width of the axle (flange to flange). Make sure the new one is the same size there.

Do you have a frame and axle shop anywhere nearby? For $1000 you should be able to get a good shop to install a decent locker and new gears. I certainly wouldn't pay that kind of money for a junkyard one!!