Synthetic Fluids Recommended?

[redfishsc]

Anyone have any links to rebuild kits for the posi can't afford a new maybe this will get me buy

Are you sure you have a Posi? I would most certainly pull the rear diff cover off, swap the oil, inspect the ring and pinion gears. Most likely you either have a G80 locker, or a straight open diff. They are very easy to identify, the G80 is a pretty distinct looking contraption, as is the open diff. Neither look anything like a posi.

 

[Sampuppy1]

I have a thread for this somewhere. I'll go dig it up. You guys have some. Really good info in here.

Sent from a flagged XT1254
Tyler/T-Unit

 

[Sampuppy1]

http://www.gmt400.com/index.php?threads/20114/

Sent from a flagged XT1254
Tyler/T-Unit

 

[michael hurd]

So far as I know, this doesn't apply to GM stock rear ends.

I cannot speak to his year model (88) but I'm almost certain you either got a G80 Locker (not a posi) or an open diff (not a posi). You can most definitely run synthetic in either a G80 or open diff, no problem, and probably handles heat a lot better.


A few months ago I pulled the old G80 out of my Suburban and put a Detroit (Eaton) Truetrac in, and the instructions included said basically the same as above. The Truetrac is a posi, except it uses torsion gears/pinions for friction. I'd rather run synth but I've read enough stories that the Truetrac doesn't like synth at all.

It has been my experience, the G80 is a bit cranky at times. Installing a bit of additive hasn't produced any deleterious effects that I have come across, and it's operation is smoother than straight 80w90 out of the bottle.

I know this is anecdotal evidence offered by observation. If in doubt, call Eaton, they should be able to steer you straight.

 

[michael hurd]

Doing a bit of digging, I came across this tidbit: Post #5

https://www.plowsite.com/threads/2500hd-diff-fluid-replacement.59574/
https://www.plowsite.com/threads/2500hd-diff-fluid-replacement.59574/
"
Not a dumb question at all CK...

The term GL5 is the API rating of the oil... just like engine oil. GL5 was the most current designation for gear oil at the time our truck was produced. GL6 is now the highest rating. So you can use any oil meeting the GL5 or GL6 rated specs. It'll have the GL rating right on the bottle if you look at the label.

GM no longer recommends additives in the HD trucks after they began using synthetic oil in the rear ends along with changing the clutch material to carbon fiber in the G80 Gov-Loc's. SO no additive should be necessary for your truck. But I have heard of several Gov-Loc's with the old style clutches finding their way into 01 and newer trucks...so if by chance after changing the rear fluid you find that the Gov-Loc "chatters" or severly binds up during a tight turn, yours may have the old style clutches. If you find thats the case, simply drain a little fluid out and add the additive, it wont hurt a thing if you run it without the additive though.

"


This mirrors my experience.

 

[5spd Z71]

I've got a TrueTrac in my truck, and I'm running a synthetic, and have been for over 35,000 miles. No issues at all.