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8 3/4 Diff Gear Lube #1690206 10/25/14 12:13 AM 10/25/14 12:13 AM
Joined: Jun 2014 Posts: 52 Houston Texas, USA M markfh52 OP member
markfh52 OP member M Joined: Jun 2014 Posts: 52 Houston Texas, USA	What gear lube would be best for the 8 3/4 posi diff. I know there's a limited slip additive that needs to be used but I was checking out Castrol 75w-90 synthetic limited slip lube. Can that be used or is there a better alternative. Thanks

Re: 8 3/4 Diff Gear Lube [Re: markfh52] #1690207 10/25/14 12:20 AM 10/25/14 12:20 AM
Joined: Sep 2004 Posts: 6,906 IL, Aurora A ademon master
ademon master A Joined: Sep 2004 Posts: 6,906 IL, Aurora	I'm going to use Torco 85w-140w racing regular dyno. with a bottle of the ford juice. It's on it's way from amazon.

Re: 8 3/4 Diff Gear Lube [Re: ademon] #1690208 10/25/14 12:59 AM 10/25/14 12:59 AM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	90 weight or 80W90 will work fine for general use. I have always used the parts store LS additive in mine (GM spec?) without issue. Synthetic can help with temperature extremes: for really cold weather or if running sustained high speed/high temp. An xx/140 dino oil can help somewhat with high temps as well.

Re: 8 3/4 Diff Gear Lube [Re: ahy] #1690209 10/25/14 01:00 AM 10/25/14 01:00 AM
Joined: Feb 2003 Posts: 1,306 Laveen, Arizona GTSDart340 pro stock
GTSDart340 pro stock Joined: Feb 2003 Posts: 1,306 Laveen, Arizona	I just had mine give through this year. I put 80-90 in it with the LS additive. No issues so far! 1949 International KB-2 "Mater" - 302/T5 1968 Dodge Dart GTS "The Drat" - 340/727 2006 Dodge Magnum R/T - Hemi 2016 Dodge Durango Limited - 3.6

Re: 8 3/4 Diff Gear Lube [Re: markfh52] #1690210 10/25/14 01:05 AM 10/25/14 01:05 AM
Joined: Nov 2007 Posts: 21,822 Kirkland, Washington Pacnorthcuda Too Many Posts
Pacnorthcuda Too Many Posts Joined: Nov 2007 Posts: 21,822 Kirkland, Washington	Quote: What gear lube would be best for the 8 3/4 posi diff. I know there's a limited slip additive that needs to be used but I was checking out Castrol 75w-90 synthetic limited slip lube. Can that be used or is there a better alternative. Thanks Your choice would be fine. For the additive go to a Ford dealer and buy it, it's the original formula MOPAR used to use. If your ""posi"" is a cone type the additive you choose really doesn't matter, if it's a power lock clutch unit you want to feed it the best.

Re: 8 3/4 Diff Gear Lube [Re: markfh52] #1690211 10/25/14 02:08 PM 10/25/14 02:08 PM
Joined: Sep 2006 Posts: 3,010 Sac, CA M mopowers master
mopowers master M Joined: Sep 2006 Posts: 3,010 Sac, CA	No need for the additive if the gear oil is made for limited slip diffs. That mean there is additive already in the oil.

Re: 8 3/4 Diff Gear Lube [Re: mopowers] #1690212 10/26/14 09:04 PM 10/26/14 09:04 PM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	Regardless of what the label says, you must always add friction modifier to a bottle of gear lube. Contact info

Re: 8 3/4 Diff Gear Lube [Re: DoctorDiff] #1690213 10/27/14 10:07 PM 10/27/14 10:07 PM
Joined: Jun 2014 Posts: 52 Houston Texas, USA M markfh52 OP member
markfh52 OP member M Joined: Jun 2014 Posts: 52 Houston Texas, USA	So if I use Castrol Syntrax Limited Slip 75W-90 I should also use something like Champion Limited Slip Differential Axle additive concentrate or like the Ford additive as suggested.

Re: 8 3/4 Diff Gear Lube [Re: markfh52] #1690214 10/28/14 12:13 AM 10/28/14 12:13 AM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	Yes, use the Ford additive. If you can't smell friction modifier in the gear lube, it is either not there, or there isn't enough mixed in. Contact info

Re: 8 3/4 Diff Gear Lube [Re: DoctorDiff] #1690215 10/28/14 12:19 AM 10/28/14 12:19 AM
Joined: Jun 2006 Posts: 5,161 CT GTX MATT master
GTX MATT master Joined: Jun 2006 Posts: 5,161 CT	Quote: Regardless of what the label says, you must always add friction modifier to a bottle of gear lube. Even the stuff from Richmond? Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street

Re: 8 3/4 Diff Gear Lube [Re: GTX MATT] #1690216 10/28/14 12:54 AM 10/28/14 12:54 AM
Joined: Sep 2004 Posts: 6,906 IL, Aurora A ademon master
ademon master A Joined: Sep 2004 Posts: 6,906 IL, Aurora	I just picked up the ford additive it's 4 oz and was about $6.50 from the dealer. I haven't sniffed it yet I'll report back on the smell in a few days.

Re: 8 3/4 Diff Gear Lube [Re: ademon] #1690217 10/28/14 04:32 PM 10/28/14 04:32 PM
Joined: Sep 2004 Posts: 6,906 IL, Aurora A ademon master
ademon master A Joined: Sep 2004 Posts: 6,906 IL, Aurora	Ya it smells nasty. way more smelly than the stuff i got from NAPA that they have on the shelf. Always got a bit of popping on my truck 9 1/4 rear when i make a turn on a incline, well see if the ford stuff works better.

Re: 8 3/4 Diff Gear Lube [Re: ademon] #1690218 10/31/14 02:01 PM 10/31/14 02:01 PM
Joined: Apr 2011 Posts: 1,520 West Palm Beach, Florida Copper Dart pro stock
Copper Dart pro stock Joined: Apr 2011 Posts: 1,520 West Palm Beach, Florida	IIRC. Someone mentioned that it's made from whale blubber. If true, that should explain the wonderful aroma! Eskimos use it as cologne. Yummmmm.nb Common sense, the least common of all the senses. Mom. For fear of ridicule, society stifles creativity. Ricky Valdes

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