It obviously won't harm them right away, but over the long term it's not good for them and will do damage.

Roger Brown, aka 4Crawler, has some good info about synth lubes in the tranny on his site.


4x4Wire's Toyota Section
1995 FZJ80 LandCruiser - 3 locking diffs, +200k mi, JD HIR's, 285/75R16 Nitto TG's
Olde North State Cruisers