manual transmission gear oil

[Wisha Haddan H3]

What kind of gear oil does the H3's manual tranny use? The US part # is 89021806 (Canada - 89021807) but is it synchromesh? synthetic? or can you use any 75W90 gear oil?

Just wondering if there would any benefit (or harm) using a synthetic in the gearbox.

[bjc]

I think f5 may have addressed this question at some point, but I'll jump in here since I know how hard it is to get help with 5-speed questions.

I seem to remember that the manual tranny doesn't use synthetic. Assuming that's correct, I'm not inclined to move away from the OEM fluid in favor of a "superior lubricant" (read - synthetic) because I'm already happy with how my truck shifts.

I know a few people (non-Hummer owners) that switched to synthetic with mixed results. Those that switched in the winter found their shifting improved, but it was worse in the summer when the fluid became too slick for the syncronizers.

[Wisha Haddan H3]

thx BJC, I figured as much but it doesn't hurt to ask, especially when my searches didn't bring up anything. The NV3500 5-spd in my Blazer was GM Synchromesh only and everyone I heard of who tried synthetic or regular gear oil had problems.

[f5fstop]

I would use what the OEM recommended, just change it when necessary. Which I might add is not necessarily when a dealer says to change it, go by the information in the owner's manual.