help with g80

billbarr100 · November 1, 2005

I have a 97 gmc 1500 ext cab 4x4 auto 5.7 with a 3.73 ratio G80 rear end. I had the oil changed in the rear diff and now it doesn't seem to grab. I tried putting one tire in the sand and power brakeing, but the traction tire never grabbed. I jacked up the rear and spun the the tires and got it to lock, but i had someone hold the other tire and there was only minimal resistance after it clicked and they both started to go the same way. Will the G80 additive help this, or did the g80 die the same day i changed the oil. There is just regular pensoil 75w90 in there now. Any help would be appreciated.

asilverblazer · November 1, 2005

I might be wrong but the limited slip requires synthetic diff fluid. If you do not use it then a package of diff. additive with the friction modifiers is needed. But do not use the two together. What I would do is drain it and refill it with synthetic. At least this is how my '99 is the '97 might be different.

MS3DALE · November 2, 2005

I might be wrong but the limited slip requires synthetic diff fluid. If you do not use it then a package of diff. additive with the friction modifiers is needed. But do not use the two together. What I would do is drain it and refill it with synthetic. At least this is how my '99 is the '97 might be different.

No,The G80 does not require synthetic fluid in the Old-Body-Style trucks nor does GM recommend or want you to use any differential friction modifier additives,All you need is a 80W-90 GL-4 axle lube (GM Part #89021671)

GM uses synthetic axle lube in the rear on the New-Body-Style trucks,But again,no additives at all.

billbarr100 · November 2, 2005

Just for sh*ts and giggles I tried the friction modifier. Still doesn't work. The only thing i can think of is that the old fluid was dirty and more grippy or somthing. Anyway, i'm gunna take the cover off and see if there is anything visually wrong. Then, clean it up and see if i can find someone who can rebuild it.

I've heard that there are kits out there that you can buy that rebuild them and at the same time make them work faster for offroading. (less rpm for lock) Does anyone know where to get a kit like that?