Diff additive question...

[Got5onit]

Had a new '06 diff installed in my '04 V last week. I immediately came home and changed it to Royal Purple 75w90 synthetic. When the break in period passes, I'll be switching to Red Line.

Royal Purple synthetic gear oil can be bought at O'Reilly auto parts.

[austin]

I had a 06 diff installed a few weeks ago... The service sheet list theree part numbers, one for the diff., one for the fluid, and one for the vent kit. I asked about the posi-additive, and they said it is not needed as the fluid is synthetic. Will not having the additive eventualy burn out the posi clutches?

[rand49er]

Had mine done last July, and it lists four part nos:

1) 12793756 carrier 5.505
2) 89021677 gear lubr 8.800
3) 1052358 addt 8.800
4) 25730853 vent 5.387

[Flyboy]

It NEEDS the additive! !! !

I repeat.......It NEEDS the additive! ! ! !

[ewill3rd]

Tell them to refer to SI Document ID# 1387214 which can be accessed by going to the owner's manual section in SI and searching for Lubricants.
Under rear differential they will find this EXACT TEXT:

SAE 75W-90 Synthetic Axle Lubricant (GM Part No. U.S. 12378261, in Canada 10953455) meeting GM Specification 9986115. With a complete drain and refill add 4 ounces (118 ml) of Limited-Slip Axle Lubricant Additive (GM Part No. U.S. 1052358, in Canada 992694) where required. See Rear Axle

Also refer them to Document number 803844 which is a procedure for changing the differential fluid. It states the following in RED TEXT:

Important: If equipped with a limited slip differential, limited slip differential lubricant additive, GM P/N 1052358 (Canadian P/N 992394) or equivalent must be added first. Refer to Lubrication Specifications . Approximately 0.23 L (7.8 oz) of residual fluid will remain in the differential.

(presumably because it is important)

If a parts person punches in the 12378261 part number it will change numbers to the number listed above that ends with 1677.

It does need the additive, if they don't put it in you'll have chatter problems on turns. (using the "chatters on turns" diagnostic chart takes you to the document I mentioned above.

It won't do any short term damage.
Tell them a World Class GM Tech friend of yours told you that you need the additive.