Auto tran "D" is two gears?

I'll describe as best I can.
My round trip commute is about 50 miles over mostly gentle hills.
Cruising in "D", I can definitely feel and hear the engine downshift and upshift, with an accompanying change of a few hundred RPM.
After it's downshifted, I can bump the shifter over to "4" and it downshifts further, with another rise in RPM.
I figured the L-D were the 5 gears in the 5 speed auto, but it seems to me as if the "D" has 2 gear ratios of it's own. Am I missing something or is there an O/D that isn't counted in the 5?
Thanks for any education.

 

torque converter

 

usually my truck stays in 5th(drive) because i cant feel it downshifting as i slow down unless im driving in manual, but once it comes to a stop it goes into first and once i take off it goes through the gears again, maybe thats what your talking about? but then again i could be remembering wrong

 

OK, I'll do some studying on that. I always thought "torque converter" was just another term for an auto transmission.
My mechanical background is motorcycles, so obviously an automatic transmission is still magical to me.

 

No, I can feel it downshift starting up a gentle hill, and at first I thought it was going down into 4. I tested several times by waiting for that first downshift, then clicking over to 4 to see if that's where it was, but that made it shift again even lower, so just within the D setting I am getting a shift up/down on the hills.

 

i think i know what you mean, the rpms rise but it doesnt downshift right? but this only happens to me on the freeway when i step on it a little more, after regearing my truck it does this, its pretty weird, before the gearing if i stepped on it it would downshift but now the rpms rise noticeably pretty much like a gear in between 4th and 5th but i know it hasnt gone into 4th

 

if you're still worried, i wouldn't be. mine does it, my last truck did it, i don't know the ins and outs about it but i'm pretty sure the truck is just trying to be smart somehow or another

 

Yep, torque converter locking and unlocking.

 

Your torque converter will unlock prior to down shifting.
http://en.wikipedia.org/wiki/Torque_converter

 

Thanks guys. I wasn't worried about it, just didn't know what it was, and I like knowing how all the systems work in my machines.
I'll read up on the torque converter.

 

A torque convertor and automatic transmission are not the same thing. A torque convertor is a part within an automatic transmission and more or less does the job of a clutch but is slips more than a manual transmission's clutch. What you're feeling is what Chris4x4 described.

 

The torque converter has it's own clutch, and operates as Chris said. Locking removes the torque converter loss.

 

Thank you for asking this question! I have been wondering the same thing now for quite a few months but keep forgetting to ask about it. This is my first Auto trans and i could have sworn that little inbetween gear was like a mini overdrive or something.

The answer still confuses me slightly because the "downshift" is so constant, it doesn't feel like a clutch and the rpm increase is so constant, not as if its slipping. But I'm sure its much more complex than I'm giving it credit for.

 

If you've got any experience on ice/snow or having a ton of power you can think of it like getting some tire spin when you hit a hill then the revs drop again as you crest the hill and the tire hook up again.

That's basically what's happening inside the torque convertor, the lock up clutch unlocks and then the engine picks up some rpm as you start to get some slippage in the torque convertor between the input and output side. As the load decreases (downhill, level ground, slowing, whatever) the lock up clutch locks the convertor back together to get rid of that slippage and improve fuel economy a little.

So with a given transmission output rpm, equating to say 60mph, your equivalent engine rpm would be say 2000 rpm locked up or 2000 rpm + 200 rpm of slippage = 2200 rpm, but still the same gear and same output speed.

Just like when you're driving normally the tires are going say 30 mph and the truck is going 30 mph, if you could walk on it and get some tire spin the tires might speed up to 40 mph even though the truck is still only going 30 mph.

 

Prob 4th you feel. Try downshifting into 4th from 5th goin up a slight hill and see if it feels the same as it does when you're just cruisin

 

That is exactly why I thought it was some type of overdrive like the OP. When I would shift into 4th and it would then again rev higher.

 

But if there were 2 overdrives.... you know toyota would be all over the marketing for it. But I was noticing this the other day and when I cruisin and I pushed my foot down abit and it was like a seemless downshift. Then I tried it down shifting into 4th later in the drive and it felt simular but I wasn't really watching the RPMs so maybe I was off abit. Oh well, got something to do on my commute tomorrow

 

I think I'm experiencing the Torque converter locking and unlocking?

Sometimes I know my truck has hit 5th gear or O/D, because the RPMs drop and i felt it upshift...but while in in 5th sometimes i feel like there is another smallll RPM drop, but I'm still in 5th and I know I didn't downshift. and not only can i feel it, i can hear it from my exhaust too.

 

^^ this.

The torque converter locks up in 4th and 5th gears, essentially making the automatic a direct drive connection between the engine and wheels (a manual tranny is always direct drive). I believe I read somewhere that if the engine load is less than 90% (like when you're cruising at steady speed on a level highway), it locks up. Over 90% (like when you give it gas), or below a certain speed, it unlocks. Lock up torque converters are one of the reasons automatics are now seeing better gas mileage than manuals. That, and how the computer learns your driving style and optimizes shift points.