Gottum rear end problem

Alan Addict
I need a bit of input here, got a 97 K2500, 350, auto and 14 bolt (we think) posi, 3.73 gears. Assuming it's posi because it seems to want to spin both rears under plowing loads. It started developing a noise in the rear a couple days ago. Sounds like a metallic buzzing, very much like when the t-case doesn't engage fully and the gears are just touching. Doesn't seem to be related to power input, it sounds off under low throttle as well as hard acceleration. It doesn't seem to do it at speeds over 20 or so. I'm thinking that it's a posi clutch acting up, could I be right? Also, does anyone know the build code for posi? Any fix that can be done in God's Garage (outdoors)? Not running the truck at the moment, want to get it fixed before it can do any further damamge, I'm going looking for a shop appointment tomorrow morning.


look in your glovebox there should be a sticker with codes on it if you see code G80 that is the code for a locker GT4 is 3;73 gear. it probaly is the disk that are making the noise i would get it checked out in a hurry because if it comes apart you are going to spend a lot of money to repair it .

John DiMartino Veteran
Alan,Id pull the cover and have a look,see whats going on,and check the fliuid condition,and the magnet for lots of metal.Any chance its your brakes or U-joints?I assume you already checked the fluid level and its full.Do you have the full floating 10.5".semi 10.5" or the semi floating 9.5"?The G80 locker's hold up well in 3/4 HD and 1 tons.The clutches arent engaged unless you have a 50RPM axle speed difference between the left and right axle.Until that time,it does nothing at all,and it functions as an open differential.If the clutches are gone(not likely) then they might be falling out and getting ground up in the rear.Good luck.

Randy Scott

Senior Member
Germantown, WI
My buddy and I both had the same kind of noise on our '98 GMC's and both trucks, like clockwork, had chattering in the rearend at 8000 miles(we both bought them new). Both trucks have 3.73 gears with the posi.(limited slip, whatever you want to call it) We had the fluid changed under warranty and it went away. Then at about 40,000 mine did it again, changed the fluid again and sold the truck at 60,000. My buddy still has his and has about 45,000 and it hasn't done it again. Just my experience.

Alan Addict
Well,, just checked and we DO have posi. Thank you 4x4k20. John, we've eliminated u-joint and driveshaft problems. This is a semi-floater, which was somewhat of a surprise on an 8600 gvw truck, I thought sure they were using full floaters on them. Whatever this is it makes a very rapid buzzing sound, exactly like a transfer case not quite engaged and buzzing gear teeth. Currently has 88,000 on the clock. Two GM shops locally, we're currently battling with one over a HUGE repair bill that didn't fix anything (haven't paid it yet either) and the other one has a pretty sketchy history of doing things right. Couple of local independant shops I trust but they are both usually booked in advance (figures). And I don't do gears or engine internals myself (a man has to know his limitations).

TLS Addict

This noise is speed related right? If its not, its not your rear or driveline. Do you need a load for it to make the noise? Can you just jack up the rear and let it run and listen to the noise? How often have you listened to the grinding noise that a transfer case makes when it is partially engaged? I don't care how fun it is to listen to, its a very harmful noise that I try not to listen to in my truck!! LOL

Good Luck

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