Tow/Haul off or on(ram)

[stevemorris]

I w the discussion about the ford tow/haul system, how about the Ram
in our case, 2017 1500 with the hemi and 8 speed

we use T/H all the time when towing and definetly see a difference in acceleration and braking, shifting at higher engine speeds and earlier downshifts

we also use the manual shift buttons on very twisty steep hills for engine braking and going up those steep hills

but does it do anything at highways speeds on flat roads?

[opnspaces]

hotpepperkid wrote:

Lynnmor wrote:

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.

Must be a very old one. Even my old Ford 2000 has a locking torque converter. It locks up even when OD is off

I find this whole topic interesting and a bit amusing with all the differing opinions. I haven't worked on cars and trucks since the late 90's and undoubtedly some of what I know is now outdated. But my thoughts anyway.

Why do people always feel the need to second guess the engineers that designed and tested a system (Tow/haul in this instance)? I mean yes in the first few years of a new design there might be fine tuning to happen and bugs to work out. But we've had tow/haul mode for years now. It works, they even named the button something simple so the general population who we all know never read the manual can know what it does. It's simple, when you hook up a trailer turn on tow/haul. when you disconnect the trailer, turn off tow/haul. How hard can this be?

This one truly is academic, does a transmission have direct drive? The answer is maybe, but the question is does it matter? My old Bronco with a three speed C4 transmission has direct drive. It's very inefficient and makes the engine rev high on the freeway wasting fuel and generating a bunch of noise. Who cares if the modern transmission with eight or ten gear ratios has a 1:1 ratio? It changes nothing if the ratio is .98:1 or whatever is close to 1:1. Transmission heat is caused by slippage which is normal in an automatic. The slippage near 1:1 is extremely minimal.

An unlocked torque converter is a big source of heat in the transmission. keeping it locked lowers temperatures. But really the biggest reason for a locking torque converter is to help meet the CAFE (Corporate Average Fuel Economy) standards for the manufacturers fleet. Because it eliminates slippage it saves fuel.

stevemorris wrote:
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

This is to be expected. Tow/haul changes shift points. if you're just cruising on flat ground it's not going to change anything.

samspade wrote:
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 ??

Going off what Samspade says here. There used to be a test in the 90's to see if the converter is in lockup that may still be relevant today. I'd check it but I don't have a vehicle manufactured in the last 20 years to do so. Cruise down the highway and wait until the tachometer settles at the lowest RPM for the speed. Then while keeping your right foot steady on the accelerator use your left foot to gently press the brake pedal enough to light the brake lights but not enough to apply the brakes. If the converter unlocks you should see a slight jump in the RPM's on he tachometer. Take your foot off the brake and the tach should drop back down after a few seconds.

[ShinerBock]

With my built and tuned trans, the major difference between normal and tow/haul mode 2nd gear lock-up in tow/haul mode. In normal mode it locks in 3rd while accelerating which is ideal unloaded since you go through 2nd so fast.

The upshift points are very similar, but the downshift points or more aggressive. My line pressure is the same at 250 psi max regardless of mode(which is what helps the clutches handle the added power I have in the engine). I believe a stock 68RFE line pressure is up 115 psi in normal mode and 130 in tow/haul, but don't quote me on that. I know the stock valve body on the 68RFE will only handle up to around 170 psi . I am not sure what the ZF 8 speed line pressures are.

[crazyro]

If towing, tow haul mode on. If not towing, TH mode off. It doesn't matter if hills, flat, rain, shine. Shifting patterns are different in TH mode (longer time between shifts, higher RPMs, etc.). It's why it's there. Use it...

[JIMNLIN]

afidel wrote:

Sam Spade wrote:
Regardless of what vehicle you have, I think you should only use tow/haul or OD off modes if you actually see some NEED for that......like the engine is lugging going up small hills.
I would think with an 8 speed transmission it should handle most situations without intervention.

Wrong, you should always engage TH when towing, it is what the manufacturer recommends and how the vehicle is designed. The fuel efficiency focused shift patterns of the details maps are not appropriate for towing and the extra heat generated by the torque converter when not locked under load is not good for engine or transmission. In addition at least on my vehicle the hill assist feature is pretty worthless unless in TH mode.

How can Sam be wrong when your both saying T/H should be used or did I miss read what your both saying.

[afidel]

Sam Spade wrote:
Regardless of what vehicle you have, I think you should only use tow/haul or OD off modes if you actually see some NEED for that......like the engine is lugging going up small hills.
I would think with an 8 speed transmission it should handle most situations without intervention.

Wrong, you should always engage TH when towing, it is what the manufacturer recommends and how the vehicle is designed. The fuel efficiency focused shift patterns of the details maps are not appropriate for towing and the extra heat generated by the torque converter when not locked under load is not good for engine or transmission. In addition at least on my vehicle the hill assist feature is pretty worthless unless in TH mode.

[wnjj]

twodownzero wrote:
I've yet to see any transmission that didn't have a direct gear.

GM 6L80E, according to this site: https://www.monstertransmission.com/Transmission-Gear-Ratios_ep_52.html

Now you have heard of one.

[Range_Maggot_Bo]

Tow/Haul mode and exhaust brake on all the time for me.

[twodownzero]

Lynnmor wrote:

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.

Automatics do not have "gear sets"

Sam Spade wrote:

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 ??

Torque converters have been able to lock in at least direct and overdrive since there have been lockup torque converters.

Lynnmor wrote:

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.

I've yet to see any transmission that didn't have a direct gear.


OP:
Tow haul mode should be used any time you're doing towing or hauling. You should not have to force a downshift on a modern transmission.

[kodiakcanuck]

stevemorris wrote:


I believe t/h mode also disables the cylinder deactivation but I'm not sure

Yes it does. I use it all the time when towing, no matter what the road conditions are like. I believe it does keep it out of the highest gear, but regardless the transmission runs cooler with it on (less O/D gear hunting) and it should also help in an emergency stop with downshifting.

[Frostbitte]

I use Tow/Haul all the time when towing either my 5'er or cargo trailer for all the good reasons already posted. Even on flats I use it.
I couldn't imagine towing anything these days without a vehicle that has some form of tow/haul mode or another.
To answer your question on driving on the flats. It might keep your converter locked at the higher gears allowing the engine to hold the right gear suited for your driving conditions (wind, slight inclines/declines).
Leaving it on while you're towing even on flats might keep things optimal for towing in those conditions present at that time. If you turn if off, even the slightest change might make the transmission downshift or try to upshift when you don't want or need it to.

[JIMNLIN]

IdaD wrote:

Dave H M wrote:
This thread was interesting from the standpoint of how much bad information and lack of knowledge was expressed. :S

Perhaps interesting but certainly far from unique on this site.

LOL...yeah the OP has a 1500 Ram hemi and 8 speed tranny which will have different TC lock/unlock and shift parameters in T/H mode than a Ford or GM.
My wifes 2016 1500 chevy 5.3 6 speed tranny T/H mode is nothing like what my neighbors 2016 2500 Damx/A work truck T/H mode...apples vs pickles.
He also has a 2018 2500 chevy 6.0 (his wifes) and its T/H mode operation is different than the 5.3/6 speed or the Dmax/A.
Now throw in a Ford or older Dodge/Ram or a GM and we have input all over the place.

[Grit_dog]

larry barnhart wrote:
I use tow mode when we tow. neighbor has a 2008 ram 5500 and a new just bought a 2019 5500. He can't tell any difference on the 08 towing or not and solo driving on the trip home same story but not towing. I don't understand why not.

chevman

Likely because the Aisin trans (in both trucks) is already tuned from the factory to shift more like a heavy duty truck transmission resulting in less difference between normal mode and tow haul.
Aisins rev higher between shifts and keep the converter locked more than some other transmissions in "normal" mode.
And other than more aggressive downshifting and delayed shifting into the upper gear or 2, most transmissions will upshift about the same with respect to the load and % throttle when taking off from a stop with a load.

[thomasmnile]

The owners' manual doesn't explain the function and how and when to use it?

Just sayin'.....

[wanderingbob]

I use Tow/Haul going up hill but on downhill it is much to aggressive resulting in revs that do not appeal to me .