Rear diff fluid
Le Mans Master
Joined: Jan 2005
Posts: 5,479
Likes: 13
From: Dallas/Grand Prairie Texas
Your manual says to use it, I'd use it.
Better to not take chances. I'm sure you'd be okay either way, but you can never be too safe when it comes to this stuff.
I was at 21st CMC a few weeks ago and they used Redline and the additive both.....they should know better then anyone.
Better to not take chances. I'm sure you'd be okay either way, but you can never be too safe when it comes to this stuff.
I was at 21st CMC a few weeks ago and they used Redline and the additive both.....they should know better then anyone.
Melting Slicks
Joined: Mar 2001
Posts: 2,978
Likes: 280
From: Tulsa OK
I would use the GM additive, too. I just bought a stage 2 differential from DTE with 3.90 gears and they use redline synthetic gear lube AND the GM additive. It was what they say to use when servicing their differential every 15k miles, also.
Originally Posted by jefsvet
Hello I just ordered some Amsoil transmission and diff fluid. I bought the 75w90 synthetic EP gear lube, do I need to add the GM posi (or similar) additive still?
TIA
TIA
Safety Car
Joined: Sep 2001
Posts: 4,411
Likes: 1
From: Wilmington NC
Originally Posted by JoshVette
Your manual says to use it, I'd use it.
Better to not take chances. I'm sure you'd be okay either way, but you can never be too safe when it comes to this stuff.
I was at 21st CMC a few weeks ago and they used Redline and the additive both.....they should know better then anyone.
Better to not take chances. I'm sure you'd be okay either way, but you can never be too safe when it comes to this stuff.
I was at 21st CMC a few weeks ago and they used Redline and the additive both.....they should know better then anyone.
Le Mans Master
Joined: Jan 2005
Posts: 5,479
Likes: 13
From: Dallas/Grand Prairie Texas
Originally Posted by Richin Chicago
Be careful with this. As long as you can do tight slow turns and don't hear any differential noise you have enough friction modifier. If you add more you come to a point where you have no limited slip and you will just being running a wide open differential. In this case more is not better!
What you do is this:
take off the top plug first
take off the bottom plug, let it drain
put the bottom plug back in when drained
put in the first bottle of 75W90 fluid
put in the additive next
put in the next bottle of fluid until it starts to run out the top plug
once it starts dripping out the top plug it's full
put the top plug back in
...and I've been told to go drive around in about 10-15 figure 8's.....so I did, I assume this slooshes it around.
that's it, not too tough.
good luck.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Safety Car
Joined: Sep 2001
Posts: 4,411
Likes: 1
From: Wilmington NC
Originally Posted by JoshVette
Just to clearify, nobody said more is better.
What you do is this:
take off the top plug first
take off the bottom plug, let it drain
put the bottom plug back in when drained
put in the first bottle of 75W90 fluid
put in the additive next
put in the next bottle of fluid until it starts to run out the top plug
once it starts dripping out the top plug it's full
put the top plug back in
...and I've been told to go drive around in about 10-15 figure 8's.....so I did, I assume this slooshes it around.
that's it, not too tough.
good luck.
What you do is this:
take off the top plug first
take off the bottom plug, let it drain
put the bottom plug back in when drained
put in the first bottle of 75W90 fluid
put in the additive next
put in the next bottle of fluid until it starts to run out the top plug
once it starts dripping out the top plug it's full
put the top plug back in
...and I've been told to go drive around in about 10-15 figure 8's.....so I did, I assume this slooshes it around.
that's it, not too tough.
good luck.
"put in the additive next" is what can get you into trouble.
If the 75w90 already has the friction modifier ("additive") like Amsoil, Redline and several others do, adding more friction modifier can be very counter productive.
From Redline webpage:
"Do not add addtional modifier unless necessary, as too much will result in excessive wheel spin."
Le Mans Master
Joined: Jan 2001
Posts: 5,786
Likes: 6
From: Lafayette Colorado
Originally Posted by Richin Chicago
From Redline webpage:
"Do not add addtional modifier unless necessary, as too much will result in excessive wheel spin."
"Do not add addtional modifier unless necessary, as too much will result in excessive wheel spin."
Keith
Le Mans Master
Joined: Jan 2005
Posts: 5,479
Likes: 13
From: Dallas/Grand Prairie Texas
I did both and don't have any problems, and as I stated before, I was at 21st CMC LPE shop and they used Redline and the additive on one of there 427 Twin Turbo'd vettes 1100HP.......maybe they just don't know what they're doing....
Le Mans Master
Joined: Jan 2005
Posts: 5,479
Likes: 13
From: Dallas/Grand Prairie Texas
I did both and don't have any problems, and as I stated before, I was at 21st CMC LPE shop and they used Redline and the additive on one of there 427 Twin Turbo'd vettes 1100HP.......maybe they just don't know what they're doing.... 
Le Mans Master
Joined: Mar 2002
Posts: 5,266
Likes: 1
From: Kennesaw Ga
Originally Posted by jefsvet
Hello I just ordered some Amsoil transmission and diff fluid. I bought the 75w90 synthetic EP gear lube, do I need to add the GM posi (or similar) additive still?
TIA
TIA
Nope!
