richzo6

I have a z16, I auto cross, I drag race, I’m getting ready to put the mobile 1 atf synthetic in my tranny, while I’m there, are there Any advantages to changing diff oil, thinking of red line 7590, with hypoid modifiers, is there a need for additional GM diff additives?

FasterIsBetter

I just changed the tranny and diff oils in my '03 Z06. I put Red Line ATF in the trans. and Red Line 75W90 in the differential. The Red Line 75W90 has the limited slip modifiers in it already, so you don't need to add any of the GM stuff.

Be careful when buying the Red Line gear oil. They also make an oil marked 75W90NS. This is for manual transmissions only (NOT for C5's -- good for other syncho transmissions, I use it in all my old Jags and my Ferrari). You do NOT want 75W90NS for the differential. You must be sure you have the 75W90, and the container will say "GL5+ Hypoid gear oil". That's what you want.

If you haven't changed the differential fluid in a while, do it. My car is an '03 with 17K miles on it, and I was surprised how dirty the fluid was. It may not make the car run better, but why not run clean oil? It's a 5 min. job if you're under there anyway, and good insurance.

tlaselva

About to change my gears, so I have the Diff fluid, but I figure I might as well change the Tranny fluid also while I'm at it. How much ATF is needed?

Cobra4B

^ You'll want 4 quarts for the trans (takes 3.2 or so) and 2 quarts for the diff (takes 1.6).

The GM dif fluid is synthetic from the factory so I doube there's a true improvement in protection etc... however when it came time for me to change it I went with Amsoil severe-duty gear oil. I run Amsoil in the whole car.

tlaselva

Thx

vms4evr

Just a comment on you gear swap. Are you change diff gears? If so it is recommended that you do not use synthetic diff fluid for the gear break in period. Use plain old Valvoline 75W-90 with the GM additive package. Do the gear break in recommended by the vendor. Then dump the Valvoline after 500-1000 miles and go to synthetic. That was the recommended approach I got from Ikerds when I swapped ring/pinion in my C4. I followed their break-in procedure to the letter and never had gear whine or problems.

C66 Racing

On our cars the diff gets really hot due to internal friction, being mated to the tranny, lack of cooling airflow, and sitting nestled between the mufflers. Given that, I feel the diff fluid takes a beating, particularly on the track. I change my tranny and diff fluid often (at about every 4th track weekend) using AMSOIL ATF and AMSOIL Severe Gear Extreme Pressure Synthetic 75w90.

As mentioned above, the normal Redline 75w90 comes with friction modifiers in it, so I wouldn't add any unless you experience differential chatter, then add a bottle. The AMSOIL Severe Gear 75w90 also comes with the friction modifier in it and as my diff doesn't chatter, I've never added a bottle of the modifier.

Beaver06

duh...