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Ishmael
09-01-2010, 06:14 PM
I've got a 8.5" gm posi. I've got synthetic gear oil and 4 oz of limited slip addititive. Two questions:
1. Should I be using synthetic?
2. Do I use all the additive?
thanks guys
Scott

b-man
09-01-2010, 06:22 PM
1.) No.

I just recently had an 8.5 built by a pro for my Tempest with a new Eaton posi, the builder specified that no synthetic gear oil be used.

2.) Yes.

big gear head
09-01-2010, 06:36 PM
I've been using Amsoil synthetic oil in most of the rear ends that I have built over the last 13 years with no problems at all. If you got the GM additive then use it. If you got something else then take it back and get the GM additive.

CarlC
09-01-2010, 07:39 PM
bgh,

For those like myself using a synthetic rated for positraction use, if there are no chattering problems are there any needs/advantages to using an additional additive package, i.e. GM fluid?

big gear head
09-02-2010, 03:51 AM
If you don't have any chatter then don't use the additive. The additive only makes the clutches slip easier. For performance applications you want the clutches to lock up as much as possible. The additive will only hurt you in a situation like that.

My427stang
09-02-2010, 04:25 AM
If you don't have any chatter then don't use the additive. The additive only makes the clutches slip easier. For performance applications you want the clutches to lock up as much as possible. The additive will only hurt you in a situation like that.

Keep in mind that is at a cost of increased clutch wear which eventually means no more posi.

Clutch grip is almost entirely based on pressure of the beveled gears pushing outward on the clutches. In my opinion, the slight increase of lubrication during dissimilar wheel speeds and light clutch application more than outweighs the wear incurred without adequate additive.

Matter of fact, I rebuild them and even my Traction loc behind a big FE will still chirp the tires in a slow corner until it breaks loose, and I rebuilt it in 1999. That's with two bottles of Mopar additive.

My opinion is ALWAYS run it with clutch type limited slip diff and only run good stuff.

My preference is

1 - Mopar or Kendall in a small bottle
2 - Ford

I shy away from anything in a toothpaste tube

big gear head
09-02-2010, 06:11 AM
Your Ford Traction Lock has an organic friction material on the clutches and they wear much quicker than the steel clutches in the GM and Eaton units. I've rebuilt 40 year old Eaton units that didn't have enough wear on the clutches to require replacement. I've rebuilt many Ford units that had less than 100,000 miles on them and the clutches were so shot that there was no way they could lock up. The lubrication requirements for these different units are not the same. If a GM unit is working fine without the additive then it doesn't need it. For a drag racing application with little street use the additive should be left out completely. Only enough additive should be used to stop it from chattering when turning a corner. Most people just dump the whole 4 oz bottle in, and there is nothing wrong with that in a street car. The Kendall additive doesn't work well with the GM clutches. GM and Ford work fine.