LOST JEEPS
http://www.lostjeeps.com/forum/phpBB3/

High Revs Going Down Hill
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=36995		 Page 1 of 1
Author:  Wobbly [ Mon Nov 03, 2008 12:41 pm ]
Post subject:  High Revs Going Down Hill
While pulling our travel trailer, a couple times the transmission didn't up shift after cresting several hills. The RPMs stayed at 2500-3000 going down the hills until the transmission decided to up shift after a minute or two.

This is a new quirk. Is this a sign of impending transmission failure?


Thanks!
Author:  Joe Romas [ Mon Nov 03, 2008 1:21 pm ]
Post subject: 
I had that towing our camping trailer this summer. The trailer weights around #3500 pounds and after going up moutains in Virginia and West Verginia it would do that. I think what is going on is the transmission fluid is over a certain temperature and the ECM is programmed to keep the torque converter unlocked till it cools down. I think I read in the manual it's supposed to work that way :wink: I just wish the ECM programming took better advantage of all the 5 gear ratios. Too may times with OD off third gear with the converter locked and engine screaming I think 4th gear would have been a better choice. It seems to be 5th or 3rd :?
Author:  tulsa [ Mon Nov 03, 2008 2:27 pm ]
Post subject: 
4th gear might as well not exist when towing. When down shifting from 5th the transmission goes through 4th to 3rd almost instantly. The transmission will also downshift at times when going down hill with the cruise control on to reduce speed. I would rather control that myself. The transmission computer is one of the worst things about this great little beast.
Lewis
Author:  Wobbly [ Mon Nov 03, 2008 2:31 pm ]
Post subject: 
Joe Romas wrote:
I had that towing our camping trailer this summer. The trailer weights around #3500 pounds and after going up moutains in Virginia and West Verginia it would do that. I think what is going on is the transmission fluid is over a certain temperature and the ECM is programmed to keep the torque converter unlocked till it cools down. I think I read in the manual it's supposed to work that way :wink: I just wish the ECM programming took better advantage of all the 5 gear ratios. Too may times with OD off third gear with the converter locked and engine screaming I think 4th gear would have been a better choice. It seems to be 5th or 3rd :?


That's a relief. Weighed our travel trailer recently with the tanks full. It was 5100#. Tongue weight was 650#. Rear axle load was 3100# with the weight distributing hitch not fully tightened up. GCVW was 10,050#.
Author:  danoid [ Wed Nov 05, 2008 9:47 pm ]
Post subject: 
If you were using cruise control, that's a built in feature to attempt to use engine braking if you are coasting faster than your set speed. Most CRD drivers never activate it because of the built in engine braking of the exhaust system. I only get it when towing a trailer.

This feature, known internally as 'grade hunting logic' will also function uphill, by retarding upshifts if the software doesn't think the set speed can be held with the next higher gear. Most CRD drivers don't activate this one either, because of the generous low end torque of our tractor engines.

I've also been able able to hit second gear with the torque converter locked up by pulling the shifter back to '2' going uphill with a large trailer. Again, there's a calculation that looks at how deep you are into the pedal vs. how fast you are accelerating. If you are past the preset level (and know I don't know how to change that) you activate 'grade hunting' and the transmission will shift differently.

It's common with most Chrysler products. I have a hill near my house that's in a 45 mph zone and if I crest the hill with cruise on my minivan always downshifts to third.
Page 1 of 1 All times are UTC - 5 hours [ DST ]
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
http://www.phpbb.com/