Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 08-12-2002, 09:21 PM   #1
Moderator
 
jcanavera's Avatar

 
2004 30' Classic Slideout
Fenton , Missouri
Join Date: Mar 2002
Posts: 10,403
Images: 143
Send a message via AIM to jcanavera Send a message via Skype™ to jcanavera
Transmission questions

My neighbor did his first travel trailer pull this weekend. He has a 2002 Ford pickup. His pickup has a tach so he noted some reading and sounds. I can relate this also to my Chevy Express van although I do not have a tach.

Example you pull in third gear. You start up a hill and as you depress the accelerator you hear the engine seem to increase rpms but you don't see your speed increase. You also note that you really haven't dropped down to second gear at that point. My neighbor noted that his engine picked up 300-400 rpm. As your speed drops and you depress even further you encounter a downshift as the transmission goes to the next gear down. At that point I'm in second gear and I can pull the gear selector down to the 2 position and no change occurs. My neighbor tells me his Ford may pick up 800-1000 rpm at that point.

I guess our question is what is that change we feel that is not a perceptable transmission downshift like from OD to 3rd gear, but a more suttle engine noise with a perceptable increase in RPM's. Is it the torque converter coming out of a lockup but not a downshift? Inquiring minds want to know....

Jack
__________________
Jack Canavera
STL Mo.
AIR #56 S/OS#15
'04 Classic 30' S.O.,'03 GMC Savana 2500
jcanavera is offline   Reply With Quote
Old 08-12-2002, 09:50 PM   #2
Contributing Member
 
Pahaska's Avatar
 
2018 Interstate Grand Tour Ext
Austin (Hays County) , Texas
Join Date: Jun 2002
Posts: 7,164
Images: 4
Lockup

Yes, I believe it is the torque converter unlocking.

My Dodge Dakota would absolutely not run unlocked except during a shift, but both my Chevy 1500 and a previous S-10 did just as you describe.

IMHO, It is better to press a little harder and get the downshift since running unlocked generates a lot of heat in the transmission fluid. I would want a transmission temp gage before I spent any amount of time in the unlocked state.
__________________
John W. Irwin
2018 Interstate GT, "Sabre-Dog V"
WBCCI #9632
Pahaska is offline   Reply With Quote
Old 08-12-2002, 10:03 PM   #3
Moderator
 
jcanavera's Avatar

 
2004 30' Classic Slideout
Fenton , Missouri
Join Date: Mar 2002
Posts: 10,403
Images: 143
Send a message via AIM to jcanavera Send a message via Skype™ to jcanavera
Re: Lockup

Quote:
Originally posted by Pahaska
Yes, I believe it is the torque converter unlocking.
IMHO, It is better to press a little harder and get the downshift since running unlocked generates a lot of heat in the transmission fluid
I thought the heat we were trying to avoid was the heat generated due hunting between gears, for example allowing the trans to go from OD to 3rd back to OD etc. What you are saying is by getting the downshift you effectively have locked up the torque converter at the same time you downshift?

Its awfully hard to keep the trans from unlocking the torque converter since I don't feel that in the cases where have heard the converter unlock, we haven't dropped enough speed to do a manual or automatic downshift into second gear. Especially when you are running at 60-65 mph when this occurs.

Jack
__________________
Jack Canavera
STL Mo.
AIR #56 S/OS#15
'04 Classic 30' S.O.,'03 GMC Savana 2500
jcanavera is offline   Reply With Quote
Old 08-13-2002, 06:24 AM   #4
Contributing Member
 
Pahaska's Avatar
 
2018 Interstate Grand Tour Ext
Austin (Hays County) , Texas
Join Date: Jun 2002
Posts: 7,164
Images: 4
TC Slippage

There was quite a long thread on rec.outdoors.rv-travel a couple of years ago regarding running with the torque converter unlocked. I came out convinced that, whil it isn't as bad as the transmission hunting, slipping isn't real good because it generates heat.

The way I would interpret it is that the lockup is to improve efficiency. When the TC is unlocked, some power is going somewhere other than the wheels and it is obviously being lost in the transmission. The only way that that lost power can manifest itself is heat. Undoubtedly, that is why we have (or should have) transmission coolers on our tow vehicles.

I'm not suggesting that we shift down in every unlock instance (I don't); but, If the climb ahead is going to be a long one, that is probably the time for to downshift to minimize heat buildup. Most of our Texas Hill Country climbs are too short to worry much.

Somewhere in the shop is a transmission temp gage that I once used on the S-10. I should find it and get it installed on the Silverado.
__________________
John W. Irwin
2018 Interstate GT, "Sabre-Dog V"
WBCCI #9632
Pahaska is offline   Reply With Quote
Old 08-13-2002, 07:19 AM   #5
Rivet Master
 
LOST , Hawaii
Join Date: Jun 2002
Posts: 2,193
Internally the torque convertor is like two sets of fan blades. The engine drives one side, the other side drives the transmission. Set two household fans facing each other, turn one on, it will 'drive' the other. In a torque convertor, transmission fluid transfers the energy between the blades. That is why it gets hot when the clutch is unlocked (the lockup convertor orginally was designed to prevent the 3-400 rpm increase you mention, help the manufacturers meet the mandated mpg requirements).

Short periods of driving with the convertor unlocked will not harm the fluid, there are 10-12 qts. in the trans, sump, and convertor. But as John said, if it is going to be a long uphill pull, it will keep the temp lower if you downshift.

John
74Argosy24MH is offline   Reply With Quote
Old 08-13-2002, 08:27 AM   #6
Moderator
 
jcanavera's Avatar

 
2004 30' Classic Slideout
Fenton , Missouri
Join Date: Mar 2002
Posts: 10,403
Images: 143
Send a message via AIM to jcanavera Send a message via Skype™ to jcanavera
I guess what is surprising to me is that it seems that the torque converter comes into play even if you are driving in 3rd gear and not overdrive. I always had assumed that it was only engaged once you got to speed and had selected the overdrive setting on your gear shift.

In essance I always tow in 3rd rather than O.D. to avoid hunting but still have to deal with the lock up issue.

Jack
__________________
Jack Canavera
STL Mo.
AIR #56 S/OS#15
'04 Classic 30' S.O.,'03 GMC Savana 2500
jcanavera is offline   Reply With Quote
Old 08-13-2002, 09:36 AM   #7
Rivet Master
 
LOST , Hawaii
Join Date: Jun 2002
Posts: 2,193
The convertor is the source of power transmission until you get to a steady speed and the clutch locks up.

Remember the reason for this setup, mileage improvement so the manufacturers can meet CAFE. It is better to have the clutch disengage and the engine increase 300-400 rpm with the convertor than it is to have the trans down shift and have the engine increase 1000-1100 rpm.

John
74Argosy24MH is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Safari VS. Classic Questions kkrogh Our Community 24 12-20-2005 11:10 AM
Questions from the UK from a 1st timer! 1984air310 Airstream Motorhome Forums 41 03-04-2004 10:56 AM
Transmission cooler thenewkid64 Mechanics Corner - Engines, Transmission & More... 13 11-10-2003 09:37 AM
Safari questions Robin & Jerry Our Community 6 01-22-2003 09:46 AM
Transmission repairs rdm Mechanics Corner - Engines, Transmission & More... 0 05-12-2002 08:51 AM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 08:33 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.