limited slip additive req'd or recc?

[jsmiracle]

I have a 2005 2500HD CC D/A 4x4 with about 4000 miles. I love it. I am planning on towing my 8k lb. TT about 1700 miles in October. I am planning on changing out the rear diff fluid and I was wondering whether to use the limited slip additive to the oil. I plan to use Amsoil Series 2000 Syn. 75W-90. 1) Do I use the limited slip additive? 2) How much fluid is recc? (Dealer seems to be unaware of TSB's) and 3) Do I change the rear diff fluid before or after the lengthy tow trip (or both). Thanks in advance. Jim.

[Lawnboy]

Change it now. (Not positive on how much w/o looking it up)
Don't add any additives.

[DmaxMaverick]

Lawnboy is correct.

Your change is "overdue". I suggest changing before, and after your trip, if you haven't towed heavy before. If you've towed heavy for at least a couple hundred miles, one change before your trip should be OK, then a regular interval. You'll understand once you dump the lube.

No additive is required, nor recommended, whether you have a locker or not. I've used the Amsoil Series 2000 for about 75K, and recently changed to Amsoil Severe Gear, which replaced Series 2000 a few months ago. Good stuff. Some internet stores (including www.lubricationspecialist.com (http://www.lubricationspecialist.com) , a DP advertiser), still show the Series 2000, but you should receive the Severe Gear lube instead. If you receive Series 2000, the dealer is purging old, outdated stock. I still have half a case of Series 2000, and will use it in other app's where it isn't as critical.

Your fill should be about 3-3/4 qts. 4 qts. will fill it to just about the fill hole, but recent findings show a little less minimizes the chances for seal failure. Many factory fills have been in the 2 - 3 qt. range.

[jsmiracle]

Thanks... I changed the RR diff fluid this past weekend. I measured about 2.5 qts. out and put about 3.5 qts. in (minus a liitle for fluid left in the pump, etc.). I used Amsoil Severe Gear Syn. 75W-90. Thanks again, Jim.

[MikeC]

I just changed diff lube at 3100 total miles and 700 of that towing 9500# camper. OMG what a clump of wear particles on the magnet.

I replaced the factory fill with Amsoil 75W90.

Only question is, was putting 4 Qts in a bad thing?

Mike

[madmatt]

Only question is, was putting 4 Qts in a bad thing? Maybe,,,,GM lowered the recommended amount to 3.1qts to help prevent axle seal leaks. Some trucks I've seen have been fine when filled the the fill hole, others wouldn't stop leaking till the fill level was lowered. The spec should bring it to about 1.4-1" below the bottom of the fill hole.