[396 Hawk]

Even though I don't track my Hawk (for now), I figured I would ask some of you race guys what you use in the tranny (M6) and rear (4.10 10-bolt) of your cars.

I'm going to change all of my fluids in the next week or so and have used Redline in the past with pretty good results but have been considering Royal Purple.

Any suggestions?

[sgarnett]

The gear oil choice for the rear depends on the diff your are using. I used Redline Heavy Shockproof with the OEM T2, and I use Redline 75W90NS (nonlimited slip additive) with the T2R.

I am currently using Redline High-Temp ATF (basically a thicker version of D4) in the tranny to help quiet the trashed input shaft bearing (damaged by a defective pressure plate almost two years ago, but it hasn't blown up yet) and reduce the false knock-retard when the bearing is rattling. It shifts marginally OK when warmed up, but really sucks when cold. Reverse can be a real struggle on a cold day.

D4 was better.

By far the best-shifting fluid I used was conventional, non-synthetic Castrol D3. Mitch recommended it and reported that it was holding up fine on his backyard track in the Texas heat. My experience matched his - it shifted great and looked brand-new coming out.

I haven't tried the GM Synchromesh, though.

Personally, I think that while the gears may like a heavier oil film, the synchros DON'T - the thinner the better. Obviously it has to be a compromise, but the gears apparently have plenty of design margin (unless you are making a LOT of power) while the synchros are marginal from day 1. How often do you hear about somebody wearing out the gears in a T56? The T56 is supposedly a fairly efficient transmission, meaning it doesn't burn up much horsepower as heat, which means the gear train is well-designed for low friction.