Tow/Haul off or on(ram)

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 I haven't worked on cars and trucks since the late 90's and undoubtedly some of what I know is now outdated.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.