How to use Tow/Haul mode?

[danmcguire]

I have traded my 97 in for a 2005 that has the "Tow Haul" system that sseems to work quite differently from my 97's "O/D lockup system. the old truck if put into the O/D lockout, would bring the RPMs right up and keep them up and never shift into overdrive. My new truck (while not towing) when put into "Tow/Haul" seems to change the shift points for 1-2, 2-3 etc. but is goes into overdrive at about 55-60 and the rpms drop back down. I have not had chance to tow our 5th wheel yet. Does the ECM computer somehow "sense" when you have a heavy load and do something different than when you don't have on a load? I called my dealer and got a screwy answer from the service dept. that sounds like they didn't know. Dan

 

[CUMMINZ]

Overdrive

I suppose the term "overdrive" might be mis-used. The CTD has a 4 speed transmission with a locking converter. When you have the tow/haul button pushed in, how many times does it appear to change gears? When you feel it change gears about 50-60 what happens after that if you push the tow/haul button again? Might it be just locking the converter at 50 and not changing into the highest gear?

 

[BNeathery]

Dan, good question, I just purchased a 2005 and am also interested in the proper operation of the Tow Haul mode. Bill

 

[CUMMINZ]

towing

This is the way I tow my 22k grossing rig.



For the most part I tow in regular mode. If I am on a country 55mph road I run in tow/haul all the time. If the road flattens out for a good streach I will push the button to remove t/h. If I am on the interstate I run in normal mode. If I see a hill coming up that I feel my transmission might downshift I speed up about 5mph before I hit the hill. I simply listen to the engine and how it is responding and allow the locked t/c to do its job. When I feel the engine is lugging a little I will push the t/h switch and allow the t/c to unlock. And when I reach the crest of the hill I will push the button to go back to normal mode. Sometimes the transmission is fooled and little and may stay unlocked for a little to long. Simply left off the pedal just a little and the t/c will then lock.



I will say this, a stock CTD will hunt for gears under load load a little. Install about 40-60 HP chip of your choice and you will see the biggest difference in the gear hunting.



CUMMINZ

 

[GaryCarter]

Fourth gear in the 48RE is 0. 69 ratio I believe. So it is properly termed overdrive.

With respect to the 05 models, the Tow mode will make several changes to transmission programming.



Third gear (direct) TC lockup: normal mode it will not lock in third. Tow mode it will lock while in third.



OD TC lockup: normal mode locks about 50 mph (3. 73). Tow mode locks about 40 mph.



Grade braking: normal mode none. Tow mode the trans will shift down to third and lock while braking or running downhill off throttle.



If there are any changes to the shift points they are small- I don't really notice any.



If you switch to tow mode while at speed in OD the trans will drop to third (direct) with the TC locked. It will maintain third locked indefinitely as long as there is a load and you stay in acceptable RPM range. If you back out of the throttle it will shift back up to OD.



The intention of the designers -and your best bet- is to run it in tow mode while towing. That will give you lockup in third, getting more power to the ground and keeping your trans cooler.



Gary