I just found out that the T56 requires Dexron III ATF what that all about? why does a manual tranny take ATF and not gear lubricant??

Some transmissions use gear oil, some use regular engine oil, some use ATF. I guess it comes down to the parts inside and the passages/clearances involved. ATF is alot thinner than gear oil and has different lubrication properties. Why specifically the T56 uses ATF I can't say- but other GM transmissions in the same series of the last 20 years seem to specify ATF as well- i.e. T5's and the like.

The T56 uses ATF fliud because the blocking rings need it, At least this is what I have read in some book.

Thats funny. Ive always asscociated ATF as hydraulic fluid. weird.

<font face="Arial,Verdana" size="2">Originally posted by badazz81z28:
Thats funny. Ive always asscociated ATF as hydraulic fluid. weird.</font>

Same here but the T5s use Dextron fliud too.

One of the big reasons that the T5s and T56s use ATF over gear oil is mileage. 90W oil is a much bigger parasitic loss to pump around than the relatively lightweight ATF. And, if the trans is designed to handle it (i.e. the shear loads on the gears, etc.), then all the better- more HP to the wheels.

My old 1981 Super T10 used 90W gear oil, my '95 Accord 5-speed uses 10W-40, and the T56 was filled with Dexron IIE (since replaced with Dexron III).

Todd