When (Under normal conditions) should changing the tranny oil be done? What oil is recommended? Is there a better one to use for smoother gear engagement?

 

Spec for the six speed is Mercon ATF.
For the best, use a synthetic ATF.
For extra heavy duty use, you can use Redline MTL which is basically a little thicker than ATF. I've gone that route with my truck in both the transmission and the transfer case and like it so far. No shifting issues at all.

 

Did your redline MTL make going into gear any smoother?
Like in my "synchro 6 Sp..." thread, I am concerned that my going into gears is a little tougher (Not very smooth) than it should be. If possible, I would like to make the actual gear changes as smooth as possible while protecting my tranny.

Also, what is the frequency of fluid changes for the manual trannies?

 

I think it might be 60000 miles

 

It didn't make it any smoother and in fact made it a touch stiffer. A very slight touch. MTL can best be described as the consistancy of aprox cold 20 wt engine oil so it's not that much thicker than ATF. And it's a lighter shade of red than ATF. There's rumors of guys running gear oil in thier 6 speeds and ruining the transmission as a result so don't think that thicker is better.
What makes the biggest difference in shifting actually is making sure the the clutch completly disengages when you depress the clutch pedal. If you have a lot of free play at the top of the stroke that subtracts from the engagement point at the bottom of the stroke.

 

I believe the normal service interval for the tranny, transfer case, and differentials is 75,000 miles. The ZF-6 fluid capacity is just below 6 quarts. If you blow out tranny cooler and lines you'll need an additional 0.5 qt.

 

Do the manual trannies have a filter like the auto's? Are the filters fairly generic (i.e. can I get one at Murray's or Auto Zone)?