I just picked up the newly rebuilt 12 bolt with an Eaton posi. No fluids in it yet and need some ideas. I was thinking of non-synthetic with a posi additive to start and later switching to a sythetic. Fluid recommendations? How long till I can switch? Do I need additive with sythetic? Any brand names I should or should not use?
Thanks

I think you're on the right track to break it in with regular oil and then switch to synthetic. I use Mobil1 because it is 100% synthetic. Others like Amsoil and Royal Purple are the same, but not all are 100% synthetic FYI. If you use the full synthetic you won't need the additive.

Rod I just did the same thing today. I put in Valvoline 85-90, with the two little bottles of friction reducer that came with the Eaton unit.

Sound right guys?

Put the rear in after work and tomorrow all that is left is brake shoes and springs, bled'em and break it in.

Any recomendations on break in?

Originally posted by ACLineman:
Rod I just did the same thing today. I put in Valvoline 85-90, with the two little bottles of friction reducer that came with the Eaton unit.

Sound right guys?

Same exact thing I did...two bottles of friction reducer and Valvoline 80-90. I forget when you're supossed to change it out after break-in, anyone remember?

I just got done doing my rear end today i installed a posi unit w/4:11 gears which i bought GM posi differental additive for $5.99 from modern cheverolet in winston-salem NC know to everyone Classic Muscle its some great additive that GM uses but also you can use lukas oil treatment also but if i was you i would use 80-90w gear oil w/limited slip additive because sytectic oils cost more and does not make a difference.

Is all posi units supposed to have two bottles of the friction additive put in? I have always been putting in one :confused:

I never had a posi but, the eaton unit came with 2 so that's what I out in.

The guy who set this up for me kept all the paper work and I was so excited to get it back I forgot to get the papers from from him.

Hope someone answers these questions...

[/qb][/QUOTE]Same exact thing I did...two bottles of friction reducer and Valvoline 80-90. I forget when you're supossed to change it out after break-in, anyone remember? [/QB][/QUOTE]


Anybody??

AC, I hope someone else can confirm this, but I don't think you need to change it out right away.

As for break in, many gearsets will have a recommended break-in period before you tow with them or hammer on them. Some figure 8's to work the posi unit in. Don't put alot of miles on it initally, and let it cool between uses. Short hops with a cool off period. That's the way I was told to break it in.

If Big Gear Head sees this , he'll correct any errors.

Thanks man.

I thought it was something longer, like 100 miles or something. Oh and I think the 2 bottles of friction modifier was only for the inital break-in, and its fine to use only one after that.