Diff Oil?
Thread Starter
Racer
Joined: Oct 2012
Posts: 335
Likes: 7
Diff Oil?
I recently changed my differential oil to Castrol Syntrax 75w90 for
limited slip diff,if my 05 sits for a couple of days it still growls and binds
for the first half block when i pull out of my driveway then its fine, should I add more
friction modifier?
limited slip diff,if my 05 sits for a couple of days it still growls and binds
for the first half block when i pull out of my driveway then its fine, should I add more
friction modifier?
Le Mans Master
Joined: Feb 2002
Posts: 5,394
Likes: 281
From: cumming ga
GM had a lot of problems and seems to finally fixed it last 2 z06's have proved to be very quiet.
z51vett
Doug
Drifting
Joined: Jan 2005
Posts: 1,827
Likes: 301
From: Tucson Arizona
St. Jude Donor '08
The Castrol website does not say anything about this product having the necessary supplement. You will probably have to add the posi supplement. Don't forget the necessary figure eights in a parking lot to fully integrate it.
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
I used the Amsoil with the slip-lock additive. No noise here. 
Race Director
Joined: Sep 2000
Posts: 11,139
Likes: 1,912
From: Missouri City, TX
Race Director
Joined: Sep 2000
Posts: 11,139
Likes: 1,912
From: Missouri City, TX
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Tolero Apto Victum
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From: Woodlands TX
Melting Slicks
Joined: Oct 2010
Posts: 2,220
Likes: 16
From: Sugarhill Ga
I would try some LS additive first and do 5-10 figure eights. then make that call. I tried the BG JUNK in mine and had the CHATTER but no noise. switched to RP and it worked great.
the BG junk in my M6 was hard to shift when cold, I also drained it and used RP
good luck
the BG junk in my M6 was hard to shift when cold, I also drained it and used RP
good luck
Drifting
Joined: Aug 2012
Posts: 1,587
Likes: 5
From: central NJ
The problem with just adding additive is that (I think I read) too much can cause the seals to deteriorate. If it still is making noise, if it were me, I would change it out again and put in Amsoil severe gear WITH the 4oz additive. I just changed mine to amsoil about 2 months ago and all is good....
Premium Supporting Vendor
Joined: Aug 2001
Posts: 5,364
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From: King George VA
As indicated above, lots use this with good results:
AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 (Product Code SVGQT)
AMSOIL Slip-Lock Differential Additive (Product Code ADATB)
I use the Severe Gear 75w90 with no extra additive in my 02 Z06 at the track.
More than happy to get AMSOIL products for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.
AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 (Product Code SVGQT)
AMSOIL Slip-Lock Differential Additive (Product Code ADATB)
I use the Severe Gear 75w90 with no extra additive in my 02 Z06 at the track.
More than happy to get AMSOIL products for forum members at dealer wholesale pricing, about 25% below retail, via the AMSOIL Preferred Customer Program. Drop me a PM if interested.
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AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
C66 Racing #66 NASA ST2, SCCA T2
AMSOIL Dealer (Forum Vendor)
AMSOIL Preferred Customer Program (Members buy at Wholesale - a savings of about 25%)
Le Mans Master
Joined: Feb 2007
Posts: 8,514
Likes: 235
From: Currently somewhere in IL,IN,KY,TN,MO,AR,MS,AL, or FL
Mine was changed to the new GM stuff when it first came out and not a peep since. The new GM fluid requires no additive and has finally fixed the 50 year old issue.
Race Director
Joined: Apr 2007
Posts: 16,023
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From: Toronto, Canada
C7 of the Year - Unmodified Finalist 2021
use the new GM fluid which does not require the additive and do the figure 8's
Melting Slicks
Joined: Jun 2007
Posts: 2,673
Likes: 9
From: Upstate New York
I put the new GM fluid in mine last year when it just started making noise one day. Not a peep since. Funny how it was quiet for years and then just started doing it out of the blue. I wonder if the FM they put in at the factory just wears out with time.
..Me too. 
Retired & lovin' it!
Joined: Mar 2005
Posts: 4,474
Likes: 547
From: Jackson NJ
For whatever reason, the GM differentials in C6 Vettes & later year Caddys (not sure about C5's or earlier) are sensitive to the % of limited slip friction modifier in the gear oil. IMHO, best to stick with the Dexron LS Gear Oil, 75W-90, GM p/n 88862624. This is the later formulation that GM came out with after problems surfaced with clutch slippage in early C6 diffs. The bit about "figure 8's" is to insure that the new fluid is properly driven into the clutch packs. The TSB calls for 8-10 slow speed figure 8's after the fluid is changed.