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This may have been discussed in the past, and if so I missed it, but... I've been using Mobil 1 in the motor since new. I would like to switch to synthetic in the tranny (auto) and the rear end. No one around here has any idea at all when it comes to our cars. What Mobil 1 products should I use in the tranny and rear end? Thanks for the help.

p.s. To date the car has been perfect. Other then a failed gas cap (?) I have had no problems at all.
 

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All the feedback I've heard says don't but synthetic fluid in the transmissions unless you are operating at extremely high temperatures, that the GM A4 runs best on regular GM approved transmission fluid. I believe the Mobil differentional fluid requires the addition of a friction modifier, thus I only use Mobil in my differentials that don't require FM. If that is confirmed, consider using Royal Purple GearMax. It has the FM already mixed in and has good reports from other GTO users.
 

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Sorry for the late response to this... been at sea.

In my opinion, synthetic fluids will hold up significantly better than petroleum based fluids in the high temp conditions of a tranny (or diff). However, using the correct fluid which meets the manufacturers requirements is still necessary.

I'm not positive, but believe the GTO requires a transmission fluid meeting GM Dexron III requirements. Many synthetics, including Mobil 1 Synthetic ATF meet this standard and are appropriate for use in the GTO. Mobil 1 also makes a synthetic diff fluid that meets the requirements for the GTO, the Mobil 1 Synthetic Gear Lube LS 75w140. Mobil 1 states this fluid has limited slip additives in it, and does not normally need the limited slip additive from GM. Like AMSOIL, Mobil 1 also states that in some applications, OEM specific additives can be added.

As an alternative to Mobil 1, I know these fluids do meet Pontiac requirements for the automatic GTO:
AMSOIL ATF
AMSOIL Severe Gear Extreme Pressure Synthetic 75w140
As a note, this gear lube also has the friction modifier already in it.

Diff takes two quarts, auto tranny takes 11 quarts total fill and around 5.3 quarts for a drain and fill. :cheers
 
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