Hey guys - I'm in the middle of a clutch swap, and figured, as long as I will have the rear diff, and tranny out from under the car, I might as well change the fluids - it should be easier that way.

Here's my question.... (BTW - '99 6spd Coupe)....

Amsoil has the following recomedations on their website:
Manual Transmission,.....AF3
Synthetic Automatic Transmission Fluid
Torque-Drive™ Synthetic Automatic Transmission Fluid (ATD)
Controlled Slip Differential, Rear .....GL-5*[2][3] 75W-90
Severe Gear 75W-90

1 - Which of the 2 recomended tranny fluids are better?
2 - Do I still need to add the limited slip additive to the diff fluid?


Thanks again for everyones help........I'm sur eI'll be back with more questions before my clutch swap is done

 

I used the synthetic universal ATF for the tranny and SVG 75W-90 for the diff (no additive is required for most C5s).

 

with Dave68. I just did mine a few weeks back!!!

 

Per Subdriver the viscosity on the Synthetic ATF went down a little and is Dexron VI rated. The new Torque Drive stuff has close to the viscosity of the old Amsoil ATF that I already have in. I will use this on the next change. Hope this helps.

No slip additive is needed in the Severe Gear diff fluid. If you notice any chatter you can add it.

 

I used Amsoil ATD recently in my 98 C5. It stopped grinding in 6th gear that 50,000 mile old Mobil 1 ATF was allowing.

I also called Amsoil, they said either was better than Dexron III. Their first recommendation was Amsoil ATF.

 

I have been using the ATF in my Z06 tranny for years without any tranny problems. That said, they did recently slightly lower the viscosity when they reblended it to comply with the newer Dexron VI specifications. The ATF has a viscosity of 6.8 cSt at 212F, whereas the ATD has a viscosity of 7.4 cSt at 212F. But, despite the lower viscosity the ATF performs slightly better in the four ***** wear test.

I think for my next change I'll switch to the ATD because I want the slightly higher viscosity on the track since my tranny, even with an oil cooler, operates pretty hot. Either one is labeled by AMSOIL to be suitable for Dexron III applications so they meet your owner's manual requirements.

As for the diff, the Severe Gear 75w90 comes with friction modifier in it and for the C5/C5 Z06 I wouldn't recommend any extra additive. I have been using this fluid in my diff for years without the additive and have never had any chatter.

If you order one of the AMSOIL G2039 hand pumps, I'd cut the tip off to prevent it falling into your diff/tranny fill hole.