Differential Positraction Lube

[Wayne M.]

What would you use to bring rear fluid up 1" to plug level on a midyear posi unit ? Most SAE 80W-90 gear oils state they meet the requirements for service fill on limited slip differentials. For instance, Castrol Hypoy C is recommended for applications calling for GM #9985290 (a spec?) and MIL-l-2105 C and D. My '65 owners manual calls for meeting MIL-L-2105 B, which I guess was the best available then.

The instructions on the small 4 millilitre squeeze bottle of GM Limited Slip Fluid Additive #992694 state: drain rear, add this bottle, then fill with GM #740321. Is this a GM posi fluid ? How would it differ from the regular gear oil mentioned above, if the GM additive is used ? Would you add the "additive" even though you weren't draining the existing fluid, but merely topping up ?

I also saw a one litre container of GM differential fluid # 10950849, which claims to be good for limited slip as well as non posi rears, but no cross-reference specs are shown, and no mention of any required additive. All a little confusing.

I'm not looking for synthetics, just wanting to ensure good lubrication and posi operation while doing no harm. TIA

[Joe L.]

Re: Differential Positraction Lube

Wayne----

The part numbers which you mention are totally "foreign" to me(no pun intended). Apparently, these are GM Canada part numbers and probably differ from US part numbers due to packaging size differences. Also, there's probably no easily available cross-reference so giving you the US part numbers wouldn't do much good. In the US, the positraction additive comes in a 4 oz bottle and the positraction lube comes in 16, 24 or 32 oz bottle(I can't remember which or the US part numbers, but I'll post them after I get home).

In any event, I'm sure that the names are the same. The positraction additive is added first to an empty differential. I'm sure that you didn't mean to say that it comes in a 4 milliliter bottle(that would be a pretty small bottle---more like a micro-ampule)but whatever the size is I expect that it is close to 4 oz US measure (maybe 120 ml, or so). I always use TWO of these bottles but to each his own.

Although I am a BIG fan of synthetics, in the Corvette rear I ONLY use the GM Positraction Fluid. EXCLUSIVELY. ALWAYS. WITHOUT FAIL. ACCEPT NO SUBSTITUTES. I'm sure that it's the same as the fluid which is available in Canada under the part number which you said was mentioned on the additive bottle as the lubricant to use to fill the differential.

I'll post the US part numbers for the fluids when I get home.

[Joe L.]

Re: Differential Positraction Lube

Wayne----

The part numbers which you mention are totally "foreign" to me(no pun intended). Apparently, these are GM Canada part numbers and probably differ from US part numbers due to packaging size differences. Also, there's probably no easily available cross-reference so giving you the US part numbers wouldn't do much good. In the US, the positraction additive comes in a 4 oz bottle and the positraction lube comes in 16, 24 or 32 oz bottle(I can't remember which or the US part numbers, but I'll post them after I get home).

In any event, I'm sure that the names are the same. The positraction additive is added first to an empty differential. I'm sure that you didn't mean to say that it comes in a 4 milliliter bottle(that would be a pretty small bottle---more like a micro-ampule)but whatever the size is I expect that it is close to 4 oz US measure (maybe 120 ml, or so). I always use TWO of these bottles but to each his own.

Although I am a BIG fan of synthetics, in the Corvette rear I ONLY use the GM Positraction Fluid. EXCLUSIVELY. ALWAYS. WITHOUT FAIL. ACCEPT NO SUBSTITUTES. I'm sure that it's the same as the fluid which is available in Canada under the part number which you said was mentioned on the additive bottle as the lubricant to use to fill the differential.

I'll post the US part numbers for the fluids when I get home.

[Joe L.]

Re: Differential Positraction Lube

Wayne----

The US GM part number for the GM positraction ADDITIVE is 1052358. The US part number for the GM positraction LUBRICANT is 1052271 and it comes in a 23 oz bottle. The directions on the bottle of additive say to fill the differential with the GM #1052271 lubricant after installing the additive.

[Joe L.]

Re: Differential Positraction Lube

Wayne----

The US GM part number for the GM positraction ADDITIVE is 1052358. The US part number for the GM positraction LUBRICANT is 1052271 and it comes in a 23 oz bottle. The directions on the bottle of additive say to fill the differential with the GM #1052271 lubricant after installing the additive.

[Patrick H.]

Re: Differential Positraction Lube

Joe,

Why no synthetics in the rear diff? I put Red Line in mine last fall, and it sure quieted it down. And yes, I had changed the fluid regularly before, so I know I wasn't tossing out really old stuff.

Patrick

[Patrick H.]

Re: Differential Positraction Lube

Joe,

Why no synthetics in the rear diff? I put Red Line in mine last fall, and it sure quieted it down. And yes, I had changed the fluid regularly before, so I know I wasn't tossing out really old stuff.

Patrick

[Gary Schisler]

Re: Differential Positraction Lube

Wayne, as a side note - I just changed out my differential lube in my 66. I used Mobil 1 synthetic and two containers of GM brand posi additive. The GM stuff was only $.30-.40 more per container than the after market brand. I do prefer synthetic for many reasons, which I would gladly share with you if you care, but as Joe points out - each to his own. The GM brand is certainly good stuff. Gary

[Gary Schisler]

Re: Differential Positraction Lube

Wayne, as a side note - I just changed out my differential lube in my 66. I used Mobil 1 synthetic and two containers of GM brand posi additive. The GM stuff was only $.30-.40 more per container than the after market brand. I do prefer synthetic for many reasons, which I would gladly share with you if you care, but as Joe points out - each to his own. The GM brand is certainly good stuff. Gary

[Mike Ward]

Re: Differential Positraction Lube

Hi Wayne,

The correct GM part numbers for us Canajuns (eh!) are: 10950849 for the gear oil, this comes in one litre containers and 992694 for the posi traction additive, this is in 114 ml bottles

You will need one and a tad containers of the gear oil and one or two bottles of the posi additive to do a complete refill. These are two of the many GM parts that are actually cheaper in Canada than in the US.

Go figure.

Mike '73 coupe

[Mike Ward]

Re: Differential Positraction Lube

Hi Wayne,

The correct GM part numbers for us Canajuns (eh!) are: 10950849 for the gear oil, this comes in one litre containers and 992694 for the posi traction additive, this is in 114 ml bottles

You will need one and a tad containers of the gear oil and one or two bottles of the posi additive to do a complete refill. These are two of the many GM parts that are actually cheaper in Canada than in the US.

Go figure.

Mike '73 coupe

[Joe L.]

Re: Differential Positraction Lube

Patrick----

I really don't believe that there is anything wrong with using synthetics in a rear end. As I've mentioned many times, I'm a MAJOR advocate of synthetics. However, for one reason or another, I'm disinclined to try it in the differential. Partially, I think it's because I want to use the additive and I'm not certain of the compatibility of the additive and synthetic oil. I guess it's just the conservative coming out in me. I'm sure I'll be won over eventually. After all, the differential is the ONE AND ONLY place where I don't currently use synthetics. I have to stay TRADITIONAL somewhere! For now, anyway.

[Joe L.]

Re: Differential Positraction Lube

Patrick----

I really don't believe that there is anything wrong with using synthetics in a rear end. As I've mentioned many times, I'm a MAJOR advocate of synthetics. However, for one reason or another, I'm disinclined to try it in the differential. Partially, I think it's because I want to use the additive and I'm not certain of the compatibility of the additive and synthetic oil. I guess it's just the conservative coming out in me. I'm sure I'll be won over eventually. After all, the differential is the ONE AND ONLY place where I don't currently use synthetics. I have to stay TRADITIONAL somewhere! For now, anyway.

[Wayne M.]

Re: Differential Positraction Lube

Mike, you're probably right, even though Joe didn't give $U.S. prices for the 23 ounce posi lube and the 4 oz additive, my local GM dealer charges me $.6.73 Cdn for 1 litre of lube and $5.98 Cdn for 114 ml of the additive, (local Corvette club discount included) which calculates (adding 7% federal tax only --- eat your heart out 9 other provinces) to out-of-pocket $3.33 US for 23 ounces of posi lube and $ 4.20 US for the 4 ounces of additive.

[Wayne M.]

Re: Differential Positraction Lube

Mike, you're probably right, even though Joe didn't give $U.S. prices for the 23 ounce posi lube and the 4 oz additive, my local GM dealer charges me $.6.73 Cdn for 1 litre of lube and $5.98 Cdn for 114 ml of the additive, (local Corvette club discount included) which calculates (adding 7% federal tax only --- eat your heart out 9 other provinces) to out-of-pocket $3.33 US for 23 ounces of posi lube and $ 4.20 US for the 4 ounces of additive.