I have the locking rear diff. for towing, I got synthetic fluid- so do I use an additive or not? some people say do, and some don't... I need to know for sure so I don't mess something up

Thanks for the replies, John

 

If you have the stock locking rear diff from GM then use the synthetic fluid and don't use any additive. The GM locking rear diff is code G80 in the glovebox.

 

*figured it out*

 

alright, well I read this explanation on a FAQ website:
"99+ chevys do not use the additive. They use a synthetic lube"

"If you change over to a good synthetic, like Amsoil, don't add anything to it. The Amsoil is already more slippery than the original with the additive."

"If we are talking about GM part # 1052358 - it is only needed with the old style limited slip differential. The new trucks have a different style of locker.

This may be more than you want to know - but the reason the additive was called for was to help disengage (un-lock) the clutch. Without the additive when you came to a stop it felt like a car behind you tapped your rear bumper. I recall looking in the rear view expecting to see a VW bug stuck to my bumper - sometimes you needed two bottles of the additive to stop the problem."


so based on all that I think the straight Mobil1 will be fine since it is really slippery.

I think I'm gonna go do this here in a little bit, and I'll let you guys know if everything goes good. I've never done anything like this on a Chevrolet, so wish me luck

 

You don't need that additive due to your differential being a mechanical unit with no clutches. Some aftermarket fluids come with friction modifier in there already, just fyi. If you have a clutched posi, like an Eaton, if you don't have the additive in there the clutches will grab when you go around a corner. It chatters bassically, as they are trying to resist slipping rather than slip smoothly in the corner.
Good luck!

 

is this the fill plug? I put PB blaster on it, and tried to loosen it, but it's pretty stuck on there, and before I apply too much force, I want to make sure this is what I need to unscrew. oh, and I'm just using the ratchet, cause it fits perfectly into the hole, is this the right tool?

please respond quick, cause I'm working on the truck as we speak, thanks

-John

 

yes that is the correct hole and yes that is the correct tool

keep on trying at it

 

you might want to use a breaker bar so you save your ratchet thought

 

yeah I got the cover off, along with the fill hole, and I'm cleaning it up now before I re-install it

thanks for the help

so my next question is, do I fill the diff. until it leaks out the hole? or do I leave it 1/2" from the bottom of the fill hole?

 

fill it until it starts to leak out.