SuperNova
Lieutenant
- Joined
- Mar 16, 2007
- Messages
- 1,455
Re: Why is towing in overdrive bad?
As far as the tow/haul switch (this does NOT apply to the O/D OFF switch), all it does is modify the strategies the TCM uses to calculate shift points, line pressure and torque converter clutch engagement. This is an overly simplified explanation, but it gives you the idea. So the tow/haul switch is an input to the TCM which mostly just causes it to alter it's "Comfortable shifting" strategy to more of a "Damn the comfort, we need strength, power and durability" sort of strategy...So you get a little higher shift points, as well as earlier downshifts and you get firmer shifts and more clutch apply pressure. And the torque converter lock-up strategy get adjusted as well..
Maybe, depends on how minute a detail you want to get into..l...that will be a loooong answer if it is correct because it does different things on various trucks
Yep, and ramps up the line pressureFar as I know on our Jeep all it does is turn MDS off, keep it out of 5th gear, and move the shift points up.
Flat out wrong.....the trans pump pumps any time the engine is running...nature of the beast and a fact on virtually every auto trans built..The Dodge autos had other problems, I know one of them you couldn't idle for extended periods of time because the transmission pump didn't pump!
Yes sort of.....it also ramps up the line pressure and it does change the duty-cycled logic of the t/c clutchTow/haul mode depends on the tranny; I know on my Allison it not only increases the shift point rpm a bit, but locks the T/C so there is less slippage/heat. The Allison is pretty smart, probably other things going on with fluid pressure behind the scenes.
Once again, wrong. The trans pump is turning any time the engine is running....the concept you are getting confused is the torque converter fill circuit. The reason certain transmissions are specific about checking the fluid in either park or neutral is because one will have the torque converter fill circuit, but not the other. If you aren't filling the torque converter when you check the fluid level, it could give you a false reading. The main difference inside the trans between park and neutral is the position of the manual valve, other than that, the same stuff is spinning or not spinning in either position, also in the park position, the parking pawl is forced into place against the output drum.I tow my boat with my 1998 Dodge Ram 1500 4x4 all the time. (46RE trans)
But yeah, on mine, if the truck is in park, I don't believe it pumps tranny fluid, which is why you check the levels in Neutral.
As far as the tow/haul switch (this does NOT apply to the O/D OFF switch), all it does is modify the strategies the TCM uses to calculate shift points, line pressure and torque converter clutch engagement. This is an overly simplified explanation, but it gives you the idea. So the tow/haul switch is an input to the TCM which mostly just causes it to alter it's "Comfortable shifting" strategy to more of a "Damn the comfort, we need strength, power and durability" sort of strategy...So you get a little higher shift points, as well as earlier downshifts and you get firmer shifts and more clutch apply pressure. And the torque converter lock-up strategy get adjusted as well..