Guys, I have a WC T5 in the IROC. I know it calls for ATF. A mechanic friend told me they used to thicken the ATF in their T5 Mustangs by mixing in a little normal gear lube, about 20% of the total fill volume. He claims that regular gear lube and ATF will mix properly, and the thicker oil will help the tranny hold up longer and provides better lube on hot days. He says the only drawback is that it becomes a little stiff to shift on real cold winter mornings, until it warms up.

Opinions?

 

I used half & half Mobil 1 gear lube and synthetic trans fluid in mine for years..... lived in the South, Southern California, and the Midwest with it like that... always worked fine for me. Hot, cold, it didn't matter.

 

Gear oil is great if you want to swell the linings of and ruin the synchro blocker rings. It might be okay if you're tearing the tranny down very regularly and replacing parts all the time but I sure wouldn't try it.

If you want thick, go with GM synchromesh.

 

I guess it might do that.... I only had mine like I was talking about for about 6 years and 60 or 70 thousand miles, including a couple of coast-to-coast trips, so who knows what the long term effects might be.