Posi additive with Mobil 1 gear lube?

I have a 98 Tahoe with the G80 Rear Axle: Positraction option. I just changed my rear and front diff. fluids today and switched to Mobil 1 75-90w. I had intended on adding a 4 oz. tube of this Equa-Torque additive made by CRC Sta-Lube on recommendation by my friend who has a 96 Tahoe.

When I read the package though, it said for use with conventional GL5 gear lube. I felt I better do some checking into the compatability or usage with synthetics before I went any further, so I left it out.

Anyone have experience or suggestions on this? What exactly does this additive do? According to the package it talks about keeping the rear posi unit from chattering, maybe just run without and see if I start to develop these symtoms?

Went to the Mobil site and found some good info there. Here is the link for those interested...

http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_75W-90_SyntheticGearLubricant.asp

Some of the key things I read that tells me I don't need the additive, it's already got it covered...

"Product Description
Mobil 1 Synthetic Gear Lubricant is a supreme performance, synthetic, multi-purpose, SAE 75W-90 automotive gear lubricant designed to meet the highest level performance requirements of modern passenger vehicles in all types of operating conditions including limited slip applications, as well as, deliver outstanding power transfer performance."

and...

"Features & Benefits
Mobil 1 Synthetic Gear Lubricant LS 75W-90 combines wax-free synthesized hydrocarbon base oils and a specially designed extreme-pressure, limited-slip, sulfur-phosphorous additive system to provide a significantly higher level of performance in rear axles and differentials versus conventional fluids."

and also...

"Excellent limited-slip performance: Reduced chatter and improved traction"

How do you change the rear DIFF fluid?

How do you change the rear DIFF fluid?

You place a drain pan under the housing, and remove all the bolts (10 in this case) holding on the cover. Gently pry the cover back near the bottom and let the fluid drain slowly watching for debris or contaminents. Yes, it will smell pretty bad! Then remove the cover completely, and clean the gasket off the surfaces usind a scaper tool of some sort. Wire brush and brake cleaner spray work well to get the surfaces 100% clean. Be sure to clean off the round magnet/trap that is on the inside of the cover well, looking for debris there too.

Then install new gasket using permatex high-tack gasket sealer to the housing side. Then lighly coat the gasket surface (cover side) with a little fresh gear lube. This way the cover easily is removed next time without damaging gasket! Assemble and torque down the bolts in a criss-cross pattern to 15-20 in. lbs.

Remove filler plug (on upper passenger side of diferential) using a 3/8 sq. drive extention. Mine was real tight, had to heat slightly with propane. Be very careful, not to far from gas tank! I put a small amount of anti-seize on plug when re-installing. Doersn't have to be torqued down real tight either, just snug. This is how a lot of people desroy oil drain plugs all the time!

Next fill with your gear lube till it begins to run out of the hole. This should be done while the vehicle is level of course! I found a nice cheap pump that screws right to the top of a qt. container of the gear lube. Makes this job a lot easier and cleaner. ($4 at Checker Auto) Think it was made by Valvoline if I remember right.

The front is much easier, just remove the drain plug, and give it plenty of time to empty. Replace the plug, then remove filler plug and pump new oil in till it runs out the hole. Thats about it!

Just wondering: what is the oil capacity of the rear and front differential? (So I know how much oil I should buy).

WoDaN

Just wondering: what is the oil capacity of the rear and front differential? (So I know how much oil I should buy).

WoDaN

Wish I could remeber for sure, but know I did not have enough the first time. I ended up going back to the store for more!

I believe the rear took a little more than 2qts. and the front took about 2. I know I have about 1/2 qt. left over, and I'm pretty sure I bought a total of 5qts. To be safe, I'd buy 6. It's a lot easier to bring one back than trying to hunt one down on a Sun. I found! :D

Well, It's been about 5-6 weeks now since I changed the diff. fluid, and for the first time I have a leaker! I think it has to be because I used the Mobil 1 syn. oil.

When I used the procedure I mentioned in the earlier post..

"Install new gasket using permatex high-tack gasket sealer to the housing side. Then lighly coat the gasket surface (cover side) with a little fresh gear lube. This way the cover easily is removed next time without damaging gasket! Assemble and torque down the bolts in a criss-cross pattern to 15-20 in. lbs."

It has never leaked doing this before, but this is the first time I used synthetic gear lube. Will have to get another gasket, and try applying different gasket sealer to both sides of the gasket this time! Anyone else ever experienced gasket leaking once switching to synthetic?

Well, found the culprit of my leak today... Cheap paper-thin gasket I bought at NAPA, and a little to rushed in putting it on I think. I took off the cover and found that the gasket had tore near one bolt hole and shifted over, and also the two edges of this gasket facing the wheels are kind of squared off. This area on both sides wasn't sealing off very well, as there are two large holes right near that area the gasket needs to cover!

These cuts on the edges are not there on the new FelPro gasket RDS 55028-1 that I bought now at Checker Auto. It is completely round on the outside dia. It is a much thicker, stronger gasket as well. Just letting the gasket sealer set up for a few hrs. before I fill up with fluid, but I'm sure we'll be good to go this time! :thumbsup:

I use Royal Purple's Max Gear oil in my diffs. It already contains the additive needed for limited-slip/posi-traction/locking diffs. I have had no problems with it yet.