Differential Fluid - 75W-90?
Thread Starter
Pro
Joined: Oct 2000
Posts: 509
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Differential Fluid - 75W-90?
Is Mobil 1 Synthetic Differential fluid (75W-90) a good fluid to run in my differential? Gonna fill it this weekend before it goes back in with all the new goodies!!!.....but need to get the fluid. I have the GM Posi additive already. Thanks for your advice! :seeya
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
Re: Differential Fluid - 75W-90? (72Shark)
I can't answer for Mobile 1, or any other synthetic gear lube. But, I can tell you that Pennzoil 80W-90 is what the additive and GM specification calls for. I have a feeling that synthetic would be OK, BUT...(big but) I have no idea how the additive will work with the synthetic since it's designed for dino oil. Dino oil is a natural blend of a wide variety of oil molecules, while synthetic is a chemically created mix of selected molecules. IMHO, synthetic should be fine for a differential, and the additive should work well with the synthetic oil.
Racer
Joined: Oct 2001
Posts: 274
Likes: 2
From: Pampa Tx
Re: Differential Fluid - 75W-90? (Rockn-Roll)
Can't speak for Mobil 1, but I learned the hard way on conventional diff oil to only use GM with the GM posi additive. Otherwise the clutches in your posi with pop and bind up.
Phlash 72 BB Roadster
Phlash 72 BB Roadster
Guest
Posts: n/a
Re: Differential Fluid - 75W-90? (Phlash)
If you want info from the guys that make the stuff you are welcome to call 1-800-startlc and follow the numbers to the tech support. You get the guys that formulated the produts at TEXACO not some book worm. They are wonderful and can cross ref too and don't get an attitude. They have great resources and info so you can make the best decision whichever product/brand you select.
Laurie
Laurie
Team Owner
Joined: Aug 1999
Posts: 28,799
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From: Fort Mill, SC via NJ
Re: Differential Fluid - 75W-90? (72Shark)
I've had Amsoil synthetic rear oil in my '69 for 2+ years.
In fact all my fluids are Amsoil.
Amsoil says you don't need the GM additive but you may put it in if you want.
I did just for peice of mind.
In fact all my fluids are Amsoil.
Amsoil says you don't need the GM additive but you may put it in if you want.
I did just for peice of mind.
Safety Car
Joined: Mar 2002
Posts: 4,411
Likes: 1
From: Okeechobee Florida
Re: Differential Fluid - 75W-90? (69er)
i also want to change mine soon....i think ill play it safe on this one and use the GM gear oil and additive...
whataya know about the tranny oil (4 speed) ?
any additives needed there?
do you use the same gear oil that you use in the rear end?
whataya know about the tranny oil (4 speed) ?
any additives needed there?
do you use the same gear oil that you use in the rear end?
Melting Slicks
Joined: May 1999
Posts: 2,897
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From: Moon Township PA
Re: Differential Fluid - 75W-90? (72Shark)
I have been using the Mobil 1 diff. lube for quite a while now. I really like the idea of it being synthetic. I also only use Mobil 1 engine oil in all of my cars.
Gary
Gary
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Thread Starter
Pro
Joined: Oct 2000
Posts: 509
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Re: Differential Fluid - 75W-90? (72Shark)
Thanks everyone!! Gonna go with the Mobil 1 today. I already run this in my tranny, and everything runs great. With that said, I'll probably get a big BOOM this evening and have transmission guts all over the street! Oops Honey, it's broken, and they only make 6-speed transmissions now........ :smash:
Burning Brakes
Joined: Nov 2001
Posts: 787
Likes: 1
From: Toronto Ontario
Re: Differential Fluid - 75W-90? (72Shark)
Here what I did I just replaced the diff fluid with a store brand Posi-75W-90 I decided not to put in the GM additive, thinking that over the years other owners must of put of ton of that crap in. So far everthing works great no chater from the diff. I will change the fluid one more time, only because when I change the fluid the last time there was a lot of white slimmy crud mixed in with the fluid.
