Proper Gear oil for the Rear

[CTSV_Rob]

Bad title, meant to ask what is the proper oil...

I just came back from goodies and they didn't carry the RP max diff fluid. They were a Amsoil dealer so I bought the Severe Duty 75W90W.

I came back to the office and read the bottle and it said it will work with "most" limited slip rear ends and if you have any chatter add the additive.

I have checked and AmsOil has a limited slip additive and I was thinking since I have AmsOil I should use their additive but I don't know.

The question is should I use the GM additive or the AmsOil additive?

This gear oil is not cheap at $18 a quart but I will do almost anything to try and keep this rear end in one piece.

I am going to put the RP Syncromax in the tranny, new flywheel, Headers... I am going to change the oil in the diff after I get a couple of miles on the above mod's. I am leaning twoard just putting the AmsOil additive in but I figured it would be good to see what experience others on this forum have had.

[darkman]

If your going to use Amsoil Gear oil I suppose you should also use Amsoil's additive. The GM gear oil, which is the only one that meets the required GM 9986115 specification, already contains friction modifiers and yet GM still calls for an additional dose of friction modifier in the OE recipe. So it follow that non-GM gear oils would also need a "second dose."

BTW the 9986115 specification requires, among other things, a higher level of temperature stability that the GL-5 specification that most gear oils do meet.

[CTSV_Rob]

I found this on AmsOil's web site:
___________________________________________
LUBRICANTS & FLUIDS
Engine Oil
Grade 1......API*[1]
Series 2000 Synthetic 0W-30 Motor Oil
SAE 5W-30 Synthetic Motor Oil
SAE 5W-30 XL Synthetic Motor Oil
All Temps......5W-30[2]
Manual Transmission,Tremec 6-Speed.....GLS[3]

Controlled Slip Differential, Rear .....GL-5*[4][5]
75W-90
Severe Gear 75W-90

[4.] Synthetic lubricant, GM part no. 12378261, specification
No. 9986115.
[5.] With complete drain/refill add 4 oz part no. 1052358
_________________________________________________

Thanks for supplying the Part number and it looks like the oil is a replacement for the GM oil, it appears they meet the GM specification according to the blurb above.

It appears the additive is required as with the GM oil. The part number they give is for the GM additive and not their own, interesting...

Thanks for your help darkman.

Combination I will go with as of right now is AmsOil/GM Additive unless I hear a reason not to.

please keep any other comments/experiences coming, thank you.

[darkman]

Originally Posted by CTSV_Rob

I found this on AmsOil's web site:
___________________________________________
LUBRICANTS & FLUIDS
Engine Oil
Grade 1......API*[1]
Series 2000 Synthetic 0W-30 Motor Oil
SAE 5W-30 Synthetic Motor Oil
SAE 5W-30 XL Synthetic Motor Oil
All Temps......5W-30[2]
Manual Transmission,Tremec 6-Speed.....GLS[3]

Controlled Slip Differential, Rear .....GL-5*[4][5]
75W-90
Severe Gear 75W-90

[4.] Synthetic lubricant, GM part no. 12378261, specification
No. 9986115.
[5.] With complete drain/refill add 4 oz part no. 1052358
_________________________________________________

Thanks for supplying the Part number and it looks like the oil is a replacement for the GM oil, it appears they meet the GM specification according to the blurb above.

It appears the additive is required as with the GM oil. The part number they give is for the GM additive and not their own, interesting...

Thanks for your help darkman.

Combination I will go with as of right now is AmsOil/GM Additive unless I hear a reason not to.

please keep any other comments/experiences coming, thank you.

Thanks for the info on Amsoil - the last time I looked I could not find anyone (including Amsoil) claiming to meet the GM 9986115 spec, but now it seems there is. On which Amsoil website did you find that info?

[CTSV_Rob]

Below is the link I copied the information from.

http://www.amsoil.com/scripts/runisa...8:CTS,CC,V,885

[darkman]

Since my post above, I have found the Amsoil reference on its website. I think it is ambigous and have, therefore sent Amsoil an e-mail inquiry that simply asks whether their Severe Gear 75W-90 is certified under, or failing that, at least meets the GM 9986115 specification. I will report their answer.

[CTSV_Rob]

It wasn't quite clear if it meets the sepc or not but the way they wrote it it "kind of" implies it. Better to confirm so thank you for sending an email to find out.

[darkman]

I may not receive an answer today, and I will be out most of tomorrow. If you need to finish up your car, I cannot imagine the Amsoil / GM additive recipe doing any harm. I just wouldn't pull into a dealership for warranty work on a broken diff with non-spec juice in the thing.

[Florian]

RP has the goop in it already...a nice feature.


F

[ahahnu]

order rp. Have it sent to you if you must. Change the fluid early and often if you hope to keep it quiet.

[CTSV_Rob]

I tried to buy the RP but Goodies didn't carrry it. They tried to push the Amsoil ATF but I bought the RP Syncromax.

I don't plan to put the fluid in for at least another week or so. I just wanted to get the trans fluid changed before I installed the tranny. Much eaiser to add the fluid while the transmission is out of the car.

Thanks all for the help so far.

[darkman]

Originally Posted by Florian

RP has the goop in it already...a nice feature.


F

If you use Royal Purple you will still need an additive because you need TWO doses of the goop to match the OE recipe in terms of friction modifier. Royal Purple, as far as I have been able to determine does not meet the GM Specification 9986115 in terms of thermal durability above and beyond the API GL-5 threshold.

[Florian]

Originally Posted by darkman

If you use Royal Purple you will still need an additive because you need TWO doses of the goop to match the OE recipe in terms of friction modifier. Royal Purple, as far as I have been able to determine does not meet the GM Specification 9986115 in terms of thermal durability above and beyond the API GL-5 threshold.

My vehicle has a locking differential. Do I need to add additional friction modifiers when using your Max-Gear®?

No. All viscosities of Max-Gear® are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary.

I dont have a Getrag rear, so my application is different.




F

[darkman]

Originally Posted by Florian

My vehicle has a locking differential. Do I need to add additional friction modifiers when using your Max-Gear®?

No. All viscosities of Max-Gear® are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary.

I dont have a Getrag rear, so my application is different.


F

Okay. My remarks were based on the requirements of the initiator of this thread who asked about a stock CTS-V differential because I interpreted your observation as being applicable to his vehicle. Apparently it was not. My mistake.

[calicadi]

I use Redline 75W90. Comes with the additive and exceeds API GL5 spec. No muss, no fuss, no fear. Still running the original the original diff, too. More SCCA champions run Redline than any other brand.

http://www.redlineoil.com/products_g...5&categoryID=6