Originally Posted by dcg9381
Manual shift is like "tiptronic" in a porsche or DSG in a VW. Basically, it's manual shifting without a clutch. You can tell it what get to go in and stay in... The computer will override if you do something dumb like try to down-shift over redline, etc.
The 68RFE seems to have the standard truck "upshift limit" - meaning it'll limit top gear, which can be useful, but isn't quite as nice as being able to command and hold a specific gear...
It looks like the Aisin (per the internet) is the same way as the 68RFE, so I had it wrong..
Now I get it
I drive a Class 8 Freightliner for work, with a 45 ft box hanging off the back, in the mountains of northern New Hampshire and Vermont. The tractor I have now has a 12 speed auto shift Eaton, that I can shift manually if I choose. In automatic mode, it is almost always in the correct gear. I can paddle shift up or down to correct if needed, and auto mode resumes. In manual mode, it will hold whatever gear is selected indefinitely. The only times that I find that feature useful is when I'm trying to get started from a complete stop, and am having traction issues in snow, ice, or mud. Then, I'll force it to third or fourth gear to increase wheel speed, and reduce torque to help prevent spinning the drive axle wheels. Also, I occasionally need to use it to limit the top gear chosen, because it won't do that in auto mode. The downside is that it takes a moment to shift being electric over air, and I'm forever chasing the correct gear when decelerating. All that said, I don't find that I have any need for the same manual shift feature in my Ram. Limiting the top gear is more than adequate for the conditions that I encounter here, and 4wd eliminates any traction troubles. Having the trans downshift automatically to the proper gear as speed decreases or load increases is much easier than having to chase it like I do in the Freightliner.