alright, when i changed my fluid. i asked a few people and they said since im using mobil 1 syn. rear fluid, i DON"T need the limited slip additive, and it said so kinda on the bottle. So i didn't get any.. Then i hear some people saying that you DO need it, (a year later) so i went out and bought some, which is would i should of done in the first place, its only like $7.. but then i hear that 9 bolt rears don't need the additive because they are cone type clutches.. So im like screw it, im gonna put the stuff in anyways. its not gonna hurt anything.. Well i havn't put it in yet.. but i noticed today when i did a burn out, that it Looked like only the right side left its footprint. that and the howling noise it makes. so.. how long does it take to screw up a rear end without the additive?? im putting it in tomorrow. but im curious how much damage i have already done

 

If it makes a howling noise already it's only time until it breaks. I honestly can't say how much damage you did, I haven't ever not used the stuff(or an oil that contains it). It making any noise at all shows that something is wrong.

 

it only howles when im spinnign the tires.. not when turning or driving..

 

if you have a clutch type posi you need the additive reguardless of what the oil maker says. the only additive i'd use comre from gm. considering the small cost and ease of putting it in i'd do it and not have any worries about do i need it or not.

 

Breathe,

As you probably know, I use synthetic in everything. You still need the additive, even in a Borg differential (or especially there, since it has cone clutches).

I've used aftermarket additives as long as they meet the GM spec, and have had no problems.

 

This simply is not true. You don't have to add something that's already in there, and the AMSOIL Series 2000 gear lube has it in there. However, that statement doesn't apply to synthetics in general, and I don't know whether or not Mobil puts anything special for posis in their lube (just saying it's posi-compatible doesn't mean it's got anything special in it).

The additive is a friction modifier, the same thing that is used in ATF. It lets the clutches slip smoothly against each other as you go around corners. That's all it does - nothing more, nothing less (in ATF, it allows the gears to engage smoothly). It doesn't have anything to do with howling. If the rear didn't pop/jerk around corners, then there wasn't a problem with not having the additive. Most likely, there was enough residual additive from what you drained to work with the synthetic to keep the posi from grabbing excessively. Either that, or the posi was shot before you changed the fluid anyway (which is why you're peg-legged now).

 

Well, Bully for Amsoil! Mobil doesn't really indicate whether or not the additives are blended in. The bottle I'm looking at (75W90) states: "Eases gear shifting and prevents chatter in limited slip differentials" In my experience, my Borg differential DID chatter without the additive, and quieted immediately after adding CRC Equa-Torque (GM 10522358 qualified) additive.

I guess that's another thing Amsoil has over Mobil 1.

 

I always run the additive in my 9 bolts. Never had a problem.

Miles
Diff Solutions

 

ok i have a 10 bolt posi and i took it into the auto shop at school and class ended b4 i finished changing the gasket and fluid so my teacher said he would finish it. i said ok cuz i thought he was going to do it but instead he let another kid do it and he didnt put my additive that i had bought in it. well 4 months later when i finaly found the unused tube of additive lying in the shop drawer i ask my teacher who had changed the oil, i went to the kid and asked him why he didnt put it in and his exscuse was he filled it to full with the oil so he had no room. but it was to late after putting in the additive about 2 months later the posi went out and now i have one new looking tire and one bald one and a noisy howling rear end.