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-   -   First gear mystery (http://www.jeepgarage.org/f73/first-gear-mystery-43978.html)

DanS 06-27-2012 09:15 PM

First gear mystery
 
Ok, I admit that I have an obsession for how things work, but I don't understand automatic transmissions. If I put mine into first gear and start up a steep hill, I assume that I am in first gear and it will stay there. However, when I reach a point where the hill starts to level off, I noticed that something inside has just downshifted - as I see and hear a 300-400 RPM drop. So what's going on? Is first gear really two different ratios?

armoredsaint 06-27-2012 11:25 PM

Re: First gear mystery
 
don't drink and post my friend ;)

savvas 06-28-2012 12:03 AM

Re: First gear mystery
 
If you are observing this while holding first gear, then it's likely the torque convertor lock up clutch engaging. With the clutch unlocked, the torque convertor allows a speed difference between the engine and the transmission but when it locks the engine speed will drop and match the speed of the transmission.

It can sound like it has changed up a gear.

DanS 06-28-2012 12:30 AM

Re: First gear mystery
 
Most excellent. Off to study torque converters next...

savvas 06-28-2012 01:35 AM

Re: First gear mystery
 
Here's an explanation of how this transmission works. Unfortunately doesnt show the torque converter...

http://www.youtube.com/watch?v=zQwN2-9mLME

77rednecktruck 06-28-2012 05:45 AM

Re: First gear mystery
 
you can't really read a general article on transmissions and expect it to apply here. Dodge transmissions are retarded and don't really follow any normal rules.

Your Jeep probably shifted into overdrive going up the hill at a slow speed and then finally realized it was in the wrong gear and then downshifted. :)

If you can't tell, I hate the transmission in my Jeep.

AAAA 06-28-2012 06:32 AM

Re: First gear mystery
 
Quote:

Originally Posted by DanS (Post 649038)
Ok, I admit that I have an obsession for how things work, but I don't understand automatic transmissions. If I put mine into first gear and start up a steep hill, I assume that I am in first gear and it will stay there. However, when I reach a point where the hill starts to level off, I noticed that something inside has just downshifted - as I see and hear a 300-400 RPM drop. So what's going on? Is first gear really two different ratios?

If the rpm's dropped at a constant mph, then that would be an up shift, not a down shift.

savvas 06-28-2012 06:59 AM

Re: First gear mystery
 
Guys ... DanS did state that he put the transmission into first gear. So it's not in Drive, and cant up or downshift.

77rednecktruck 06-28-2012 11:46 AM

Re: First gear mystery
 
Quote:

Originally Posted by savvas (Post 649152)
Guys ... DanS did state that he put the transmission into first gear. So it's not in Drive, and cant up or downshift.

So??? :) The transmission isn't smart enough to shift correctly let alone limit gears and some of the other BS it is supposed to do.

DanS 06-28-2012 05:10 PM

Re: First gear mystery
 
I think this is exactly what's happening. Obviously the car can be stopped with the engine still running, so disengagement or slippage of some type is necessary. As the car speeds up, eventually the engine and transmission speeds roughly match and can be "locked" together. I imagine what I've noticed is that point when this occurs and it feels like a gear change when I have first gear selected. Tks to Savvas and others.

DanS 06-28-2012 05:30 PM

Re: First gear mystery
 
Here's a good video about how a torque converter works (warning - heavy metal music).

http://www.youtube.com/watch?v=q2fRC...C2CB0BF60E2357

AAAA 06-28-2012 07:51 PM

Re: First gear mystery
 
Interesting video. Thanks Dan S.


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