What is the recommended/best lube and additive for a 12 bolt posi.? It's in my 67 Ragtop. Old lube appears fairly clean and no metal or abnormal wear seen. I'm changing the rear cover so naturally I want to re-service with the best available. No known or noticable problems with rear end. Cover is off. Anything I should particularly look for? Rear End is originally from a 69 Bird.

Thanks Guys
Jerry

In my 69 10 Bolts, I used GM oil (80W90, P/N 89021671) with one 4oz bottle of GM Limitted Slip Axle Lubricant Additive (P/N 1052358).

Good Luck, Daniel.

Best available would be a 100% synthetic. I use Amsoil gear lube in my new Eaton 12 bolt posi, it has the additive built into it. :thumbsup:

Best available would be a 100% synthetic. I use Amsoil gear lube in my new Eaton 12 bolt posi, it has the additive built into it. :thumbsup:

Jim, far be it from me being an authority on this, but it seems that I've been told (or read) that synthetic is an absolute no-no for rear gears? Especially with a posi.

Not at all true Kevin, old wives tales there. There is a long story that goes with Eaton and their gears. They dont have time or money or facility to test every gear lube made in the world in all of their products. So they design their gears for a certain GL rated lube. They also have a yellow tag in the box of new gears (even the one I bought) that says not to use synthetics since they have not been tested in their products. In response to that wimpy attitude, Amsoil and others Im sure, have stated that their products are warranted to work in the eaton gears. So whether its Eaton, or Amsoil in my case, the products meets the requirements of the gear maker by GL rating. The synthetic WILL run cooler, without question. Its been documented over and over again in all gear applications. If its running cooler then it is doing a better job of lubing the gears since meshing gears create heat. Less heat means less meshing and longer wear life.
Here is direct quote from the information provided by Amsoil when asked about this situation..

Many years ago Eaton tested a synthetic fluid in their LSD. The tractive coefficient of the fluid they had tested was apparently too slippery for the LS clutch packs and caused slippage and “chattering”. Eaton thereby made the less than logical assumption that this particular synthetic does not work; therefore ALL synthetics will not work. Because of this, you now see the little yellow cards that come with the LSD units that state “DO NOT USE SYNTHETICS”. Today’s advanced synthetics with friction modifiers and limited slip additive packages are more than sufficient for the high performance LSD. To take it one step further, AMSOIL has come to find that our gear lubes possess frictional charachteristics that are equal to, and in some cases outperform the Eaton factory fill bulk fluid. Eaton does not want to spend the money to run tests on all of the various synthetics that will work in the LSD. Therefore they are stubbornly standing by their old obsolete recommendation.

When it comes to the issue of warranty it is AMSOIL’s corporate stance that our gear lube WILL work in the Eaton LSD. Should you ever have a gear lube related failure with these units, while using AMSOIL gear lube, and Eaton decides not to honor their warranty as a result, AMSOIL will repair and/or replace the damaged unit. You have nothing to lose and higher performance with a much more stable base stock to gain.

AMSOIL Gear lube WILL offer maximum performance and protection in the Eaton LSD.

Thanks for the input so far... Maybe you guys can educate me a little futher.
How is a posi unit distinguished from a limited slip, spool or other wise. What I see with mine open is a half clamp on each side and it has 12 bolts with the heads on drivers side, also 12 bolts holding the cover on. I also see springs that looks sorta like manual tranny clutch disc/pressure plate springs. I dont know how to identify exactly what I have. So far its run pretty darn good though. Jim, I have about the same drive train as you. 350 TPI, 700r4 tranny and the 12 bolt. Maybe some day I can get some pics on here. I think it looks pretty good, but don't we all feel that way bout our toys.
Thanks Again guys,
Jerry

royal purple works in my 12 bolt fine

posi and limited slip are the same, just different words for the same thing. The clutch springs you see inside are the posi parts.
Post pics when you can. :)

Jim, far be it from me being an authority on this, but it seems that I've been told (or read) that synthetic is an absolute no-no for rear gears? Especially with a posi.

1997 + Ford Explorer has synthetic gear lube in the rear differential right from the factory and must be used to maintain the warranty. Many other vehicles on the road today also use synthetic gear lube.

Nothing mysterious about a synthetic gear lube. It will do everything a petroleum gear lube will, just better.

royal purple works in my 12 bolt fine

I too am using Royal Purple.

I too am using Royal Purple.

Curious....why?

royal purple works in my 12 bolt fine


Since it can't be seen working, how do you know it's working fine? I mean, as long as the rear end doesn't rapidly self destruct, I guess it would seem any gear lube worked fine.

1997 + Ford Explorer has synthetic gear lube in the rear differential right from the factory and must be used to maintain the warranty. Many other vehicles on the road today also use synthetic gear lube.

Nothing mysterious about a synthetic gear lube. It will do everything a petroleum gear lube will, just better.

Curious....why?

Since it can't be seen working, how do you know it's working fine? I mean, as long as the rear end doesn't rapidly self destruct, I guess it would seem any gear lube worked fine.

I would like to use a synthetic in my 9".
Currie and Strange both told me no synthetic :confused: , only dino lube.
I have two center sections, one has a D-locker, w/ street gears, the other has a spool w/ pro gears, if that makes any difference.

What synthetic do you suggest?

---Bill.

Am I the only one that thought this subject was kinda funny????? :)

The Eaton engineers go out of their way to recommend the use of conventional lubes with the additive for their posi's. If synthetics performed better and reduced warranty claims, Eaton engineers would recommend it. But they don't.

I'm sure Amsoil is a fine product and I'm sure their shareholders would like to sell as much product as they can, but Amsoil didn't design and engineer the Eaton posi.

As far as Amsoil's warranty,..who determines what's responsible for failures and who will compensate you for the trouble of R&R-ing the posi, time, shipping, etc.?

Lastly, how many trillions of trouble-free miles have been logged on Eaton posi's using the recommended conventional lube & additive combo?

If it works,..