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-   -   Transmission behavior while coasting (http://www.jeepgarage.org/f107/transmission-behavior-while-coasting-70091.html)

acilate 01-07-2014 01:19 AM

Transmission behavior while coasting
 
I took my GC for some light off-roading in the hills outside of Jacksonville, OR last week with a friend. While traveling on a downhill fireroad, I switched to manual mode to try to use my gears instead of braking. I noticed some strange behavior with the engine speed while doing this.

Starting off fairly slow with the engine at idle, and transmission in second gear, the Jeep would begin to pick up some speed heading down the hill, but the engine remained at idle. After several seconds (5-10) the engine RPM would jump up to 2k-2.5k and begin to slow the Jeep down. I tried this several times and was able to reproduce the issue, but I'm not sure it happened every time.

I haven't noticed this behavior before or since, though I rarely use manual shifting mode.

Is this normal? Has anyone else experienced this? Should I be worried?

StaticFX 01-07-2014 10:13 AM

Re: Transmission behavior while coasting
 
did you watch to see if it was still in 2nd?

Im going to guess, since each gear has a max RPM and min RPM, that you got close to the max speed allowed so the computer forced the engine to throttle back or shift.. and slow the jeep.

weck 01-08-2014 01:52 PM

Re: Transmission behavior while coasting
 
If you put it in second and then just let off the brake and waited for gravity to take over, chances are the transmission torque converter was not engaged. It probably needs either throttle input or some speed differential for the torque converter to lock up.

I bet the times you could not reproduce it you gave it a little gas to get moving first.

acilate 01-15-2014 12:49 AM

Re: Transmission behavior while coasting
 
That's what I was thinking weck, but I've never experienced that before. Granted, my experience with automatic transmissions is limited. I didn't know the torque converter could disengage.

StaticFX: it was definitely in manual shift mode, and I never got fast enough for the transmission to go over 3k, so I'm pretty sure it wasn't shifting at all. You should be able to start in 2nd without an issue for snow starts, so there shouldn't be a lower limit on the gear.

kennzz05 01-15-2014 01:43 AM

Re: Transmission behavior while coasting
 
if the torque converter didnt disengage than that would be the equivilent of stopping a manual transmission vehicle with out depressing the clutch. as now everything is computer operated perhaps it had to register speed before it could start slowing the vehicle

and you dont want to start in second in the snow you will be attempting to rotate the drivetrain at a higher rpm thereby increasing wheelspin and once wheelspin starts youre also putting down more torque. bottom line if the tires are going to break traction in first there going to do it in every gear


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