My commute to work is mostly flat 2-lane highway with a few small hills. The speed limit is 55 but I cruise at about 62 or so, safe enough for the occasional radar traps. I don't like cruise control with an AT because halfway up a small hill the transmission will downshift and open the throttle just so it can cut off at the crest of the hill. The sequential shift mode on the Sport AT is great because the transmission will not downshift out of 5th. The speed drops to 55 or so on the bigger hills, not a big deal.

But something does change in the transmission. It jumps from 2200 RPM or so to 2900 even though the gear indicator still reads 5. I dropped it down to 4th by hand once to see if it was lying to me but the RPMs jumped up higher in 4th, so it was in 5th. I assume the shift in RPMs was from an overdrive kicking out. Is that right? If so, are there really 6 effective gears in the Sport AT: 1-5 and 5+OD?

Thanks for your feedback,

-- Paul

 

Paul,

What you're feeling is the torque converter unlocking. An automatic transmission does not have a direct mechanical link to the engine like a manual transmission does - it goes through a fluid-filled torque converter. At a certain speed/load, an electrical signal is sent to a torque converter lockup that effectively locks out the torque converter, which is a great gas saver compared to the non-locking torque converters of the early 80's and prior. But when you are under load up that hill, the car calculates that the torque converter needs to unlock to multiply torque under those conditions.

More on torque converters:
Torque converter - Wikipedia, the free encyclopedia

 

Thanks! That explains it well. Does the transmission ever lock the torque converter in other gears besides 5th? Also, is 25% slippage through an unlocked torque converter normal?

 

yes, that slippage is 100% normal.

I would bet that the Fit transmission does lock the torque converter in other gears besides 5th when in automatic mode. You could test this yourself - try putting the transmission in 4th with the paddle shifters, be gentle on the throttle for about 10 seconds so it would lock the torque converter if it were going to, then accelerate very gently and see if the revs stay where you think they should with a direct link to the transmission. Do the same test but with heavy acceleration in 4th and see if the RPM is higher, indicating an unlocked torque converter. If the torque converter were NOT locked, then even under very gentle acceleration in 4th, the RPM would climb.

With a manually shifted 5spd automatic, I'd be pretty surprised if the torque converter didn't lock in other gears under mild load conditions, and unlock itself under higher load.

You're not necessarily getting better gas mileage even if you could keep the converter locked in 5th up that hill. The small engine in the Fit benefits from added revs in situations like that, and more RPM does not automatically mean worse fuel mileage....if you're going full throttle at 2k rpm, vs. part throttle at 3k rpm, it's likely that you're getting better economy at 3k rpm.

 

Thanks for the enlightenment...I use the paddles exclusively these days and always wondered why it felt like it was "downshifting". It behaves exactly like you describe...

 

i have an 09 Sport A/T and it does that through all gears except for 1st with me, whether paddle shifting or not.