7.5 rear end posi fluid change

Hubb79

Not-quite-so-new-guy
Jul 12, 2018
43
8
Whts up g body fam, I was about to change my rear end fluid and was trying to see how many bottles of gm lsp additive I should use, and if I go with a synthetic fluid that already has a lsp additive in it should I still add it, and some recommendations on what's the best brand of fluid to use. Thanks fam any help would be thankful
 

melloelky

Comic Book Super Hero
Oct 22, 2017
3,048
113
mass
the general idea is 2 oz of limited slip additive per quart.yes you can use synthetic that has it built in but you don't want to add any as too much isn't a good thing.most diff companies out there recommend a non synthetic 80w/90 with the additive poured in.I'm running the Lucas 80w90(non synthetic)and it has the addtive in it already.they don't recommend adding any.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,368
113
I would run the synthetic with the additive.

Only reason I would use the additive is if you're going non-synthetic or synthetic without the additive.

You can't overdo it if you add one bottle of the GM stuff (put that in first, then fill rest of way with lube).
 

Hubb79

Not-quite-so-new-guy
Thread starter
Jul 12, 2018
43
8
I would run the synthetic with the additive.

Only reason I would use the additive is if you're going non-synthetic or synthetic without the additive.

You can't overdo it if you add one bottle of the GM stuff (put that in first, then fill rest of way with lube).
Thanks appreciate the help
 

PBGBodyFan

G-Body Guru
Supporting Member
Mar 3, 2009
591
93
Wisconsin
In the last two fluid changes I used Amsoil synthetic but still put in one GM bottle of limited slip additive. I recall my rear end builder for the one recommended it even with synthetic, if memory serves me which is no sure thing.
 

79 USA 1

G-Body Guru
Sep 2, 2011
716
93
Cheektowaga, New York
With the Auburn clutch cone units I always used Mobil 1 synthetic with with about 1/2 bottle Motorcraft additive. The Motorcraft additive seemed to have a little different formulation that works quite well with both clutch type and clutch cone LSD's.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,368
113
If the synthetic already has additive in it compatible with your posi, then I wouldn't worry too much about it.

Read the labels carefully on the lube. If it needs the additive, add it.

Worst that could happen is that you change it out, and you start turning corners and get the "chunk, chunk, chunk" as the clutches bind and slip through the cornering. Drain a bit, add a bottle of LS additive, be on your way.
 

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