Just purchased my first IROC. Had it up in the air and wanted to figure out what transmission it had. I checked my shop key and it gave me an option between 4l60e and 700r4. Im not sure how to identify them or which one the car has. If someone could help me out I would really appreciate it. The car is a 1990 iroc-z with the 5.7L 350. Thanks.

 

Congrats on your purchase and welcome to TGO !

The short answer = NO third gen F body cars had the 4L60E from the factory , not a one of them .

The transmission was called the "THM700R4" up until around 1989 , and then for some unknown reason GM decided it needed to be renamed , and so the very same unit magically became the 4L60 in 1990 (or 1991 , i can't recall the exact year) . It wasn't until the fourth gen F bodies (after 1992 , perhaps 1993 or 1994 , maybe even later for all I know ?) that the transmission got electronically controlled shifting , which is when the "E" designation was added to the "4L60" name .

Edited to add ; The Torque Converter Clutch in our 700R4/4L60 is electrically controlled by the ECM , but the transmission's four speeds are mechanically shifted . In the "E" , it's the computer that decides when the shifts happen (along with of course the TCC) VS our 700R4/4L60 that uses a spinning governor , some spring loaded accumulator pistons , and the all important throttle position cable to decide when the shifts happen . I figured I'd clarify the fact that there IS one electrically controlled feature in our transmissions , but at no where near the level of the 4L60E . If you want to see all the parts of one of our transmissions taken apart check out my sticky thread at the top of the page "pictures of every component of a 700R4"

 

Thank you. That really helped clear things up. Appreciate it.