Diff Service

pistol · May 10, 2003

OK, I have a 99 Silverado (new style) and want to change the diff fluids front and rear and also the transfer case fluid. My question is ......... what should I use? I run my truck on Mobile 1 engine oil so I don't mine using "upgraded" fluids. Also, do I need to add the LSD additive to the rear (G80) diff? Thanks for the help in advance.

99silveradoz71 · May 10, 2003

GM has new autotrac fluid which is blue. It's supposed to help cure the driveline clunk- if you have it. I don't recall which diff you're able to use synthetic in off the top of my head, but I know I used mobil 1 for 1 and valvoline gear oil for the other. I don't have a locker, so there was no additive for me. Very easy to do, and I'm not the most mechanically inclined person either.

cyrylyn · May 10, 2003

I used valvoline or something in the rear, and royal purple in the front (because of availability).

SilveradoWV · May 10, 2003

I used Mobil 1 in the rear because mine came with synthetic from the factory. I dont think the front comes with synthetic from the factory but some here have used synthetic in the front? Its up to you. As for the T-Case GM has a new AutoTrak fluid as mentioned above but you might have regular old trans fluid in there. When they first came out with that new blue (AutoTrak) fluid it seemed to only go into the push button 4x4 vehicles, not sure if they are putting it in the manual 4x4 vehicles now or not. Just have to check and see whats in there now, not sure if you can use the blue if it has the red in it or not?

01_silverado · May 10, 2003

I put in amsoil the price was actually competitive as running with the GM fluids and additive. They calim up to 5 MPG better gas mileage and you never should have to change your fluid again they claim.

That is why I switched to Amsoil.

awdvkd · May 12, 2003

Mobil 1 front to rear, if you have the g80 locker you have to use synthetic in the rear. I used mobil1 ATF in the transfer case and the allison. I really felt the difference in the tranny, it shifts better and runs cooler than dino. As for the diff additive I have heard both ways. I did not use any. I mobil 1 front to rear because everybody in my family drives it and I just tell them to use mobil1 when something gets low. Plus Mobil1 is available everywhere. :thumb:

pistol · May 12, 2003

thanks for the replys........ most likely will go with mobile 1 throughout.....

points · May 13, 2003

Is ATF in the Transfer Case or do i need to go the dealer to buy their Transfer Case fluid?

:thumb:

SilveradoWV · May 13, 2003

Is ATF in the Transfer Case or do i need to go the dealer to buy their Transfer Case fluid?

:thumb:

You will just have to check it, take the fill plug out and stick an allen wrench down in there (like youre checking the level) and see if it is red or blue. Red is plain ATF (Dex III) and blue is the autotrac fluid, not sure if there is an aftermarket autotrac fluid or not, most likely you will have to get it from the stealer if it is the blue stuff.