Grit dog
Black Diamond, WA
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"but does it do anything at highways speeds on flat roads?"
Depends on the load. If the truck will pull the load in 8th gear then even in tow/haul, it will hit 8th gear.
"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.
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B.O. Plenty
Minnesota
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ShinerBock wrote:The TC clutch does not release even in normal mode as you slow down until you get down to a certain speed. Tow/haul lowers this speed threshold. The main thing tow/haul does is change shift points. It holds gears longer when up-shifting to keep you higher rpms for more power. This is better for your transmission when towing. It also downshift earlier when decelerating to help slow down the vehicle quicker. This is not good for your transmission, but it is not that bad either.
Another thing that some transmissions do in tow haul mode is increase the line pressure threshold. This changes the shifts from nice smooth shifts to more firm shifts. This is good for your transmission because it decreases clutch wear and creates less heat due to decreasing the amount of time the clutch slips at each engagement/shift. What he said....no magic, it's designed to make towing easier on your transmission. No reason not to use it.
B.O.
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stevemorris
ontario
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did a non scientific test today!
t/h on and off, at highway speed(110 kmh) flat road
rpms's the same(so same gear) and mileage according to the dash reading was identical. transmission temp the same
2017 Ram 1500 4door, 4x4, 5.7 l hemi, 8 speed
2008 KZ Spree 260
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RoyJ
Vancouver, BC
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Sam Spade wrote:kellem wrote:I use tow mode and OD off every time I tow.
Less shifting = cooler transmission.
Maybe not.
OD OFF keeps it out of direct final drive.
The torque converter is in constant use and likely will tend to make it run a bit HOTTER.
The act of shifting up and down does not itself generate any more or less heat.
I'd like to know what transmission does that.
In most, OD off means exactly that - overdrive gears are not used, only up to and including direct drive.
Again, *most* transmissions would lock up sooner in direct drive, with OD off. I've never come across one where in OD off it stays in direct but with the converter unlocked.
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Groover
Pulaski, TN
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kellem wrote:I use tow mode and OD off every time I tow.
Less shifting = cooler transmission.
Another trick for a cooler transmission is to take it out of drive if you are going to be stopped very long. I have seen that in a couple of my owner's manuals. One even warns that the transmission will overheat if left in drive too long while stopped.
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Sam Spade
North Central Florida
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RoyJ wrote:
I'd like to know what transmission does that.
Maybe I'm a few years (decades ?) behind on transmission design.
I though that the LAST thing that happened on up-shifting was locking the torque converter.....AFTER the highest gear was engaged.
Then anything that took it out of the highest gear (overdrive) ALSO unlocked the converter.
I assume you are saying it doesn't quite work that way anymore ??
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Lynnmor
Red Lion
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RoyJ wrote:
I'd like to know what transmission does that.
In most, OD off means exactly that - overdrive gears are not used, only up to and including direct drive.
Again, *most* transmissions would lock up sooner in direct drive, with OD off. I've never come across one where in OD off it stays in direct but with the converter unlocked.
You might want to check what transmissions have direct drive, mine doesn't.
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Grit dog
Black Diamond, WA
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^ But it does have a gear ratio or 2 that are close to 1:1, so what’s your point?
Many newer auto transmissions don’t have an exact 1:1 ratio gear any longer. And many do.
What is worth noting, is there is nothing magical that happens at 1:1, it’s just another step in the gear ratios from under-driven to over-driven.
And “OD off” is a thing of the past that was used on 4 and 5 speed transmissions to limit upper gear ratios. No different than manually shifting it via the gear shift or range buttons to limit the upper gear that the trans will shift into.
I’ve not seen it on any vehicles I’ve driven in recent years that have 6 or 8 speed transmissions.
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Lynnmor
Red Lion
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Grit dog wrote:^ But it does have a gear ratio or 2 that are close to 1:1, so what’s your point?
Many newer auto transmissions don’t have an exact 1:1 ratio gear any longer. And many do.
What is worth noting, is there is nothing magical that happens at 1:1, it’s just another step in the gear ratios from under-driven to over-driven.
And “OD off” is a thing of the past that was used on 4 and 5 speed transmissions to limit upper gear ratios. No different than manually shifting it via the gear shift or range buttons to limit the upper gear that the trans will shift into.
I’ve not seen it on any vehicles I’ve driven in recent years that have 6 or 8 speed transmissions.
The point is that older transmissions had a direct drive straight thru the transmission and didn't have the friction of running it thru a gear set.
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Walaby
Georgia
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I use Tow haul every time I tow.
Mike
* This post was
edited 08/08/19 03:08pm by Walaby *
Im Mike Willoughby, and I approve this message.
2017 Ram 3500 CTD (aka FRAM)
2019 GrandDesign Reflection 367BHS
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