bluesurf

I though it is supposed to drop gears when you hit the brakes for a period of time. I towed 12k and it did not drop 4 to 3 like I thought it should do. But it did drop 3 to 2 noticeably. I realize that it changes the up shift a bit. But I am curious about the down shift as I tow heavy almost daily. Any info would be great, thanks

koogala

Great question! I've wondered about that also. Maybe someone will educate
us............

goose2

I agree with you most all the time. But I must stray from you on the Hillary thing. She get's my vote.

bluesurf

anybody, anybody who tows please chime in.

koogala

well,I suppose we can talk amongst ourselves here, since no one can give us a response. I think the manual says firmer, more positive shifts. I know when I tow my tt it takes me up higher in the rpms before it shifts. I think it must send a signal to the vb or something.

Goose! You gotta be kidding me! Please say you're pullin' my chain!
You'll be driving a hybrid electric cummins! Mods will be a felony! The only hunting you'll be doing is for videos of old diesels & the way they used to be.
Guns will be archaic relics of a bygone uncivilized era.

BigGunZ

Oversimplified but........Tow/haul allows the TC to lock up in the lower gears...I believe 2 through 4 (normally only 4th locks in the normal mode) and slightly changes your shift points. It also allows your tranny to downshift like a manual.

burlhall

I don't think the tranny will downshift until you get below a certain speed. For example, it may not do the 4-3 shifit until the truck slows to approximately 50 mph (I do not know the exact speed) while in the tow haul mode. However if the truck was not in tow haul mode the tranny may not downshift until approximately 40 mph (again I do not know the exact speed).

BigGunZ

In the normal mode, the TC unlocks at 40 mph.....that's what you feel. There's no other event that can be felt during the decelleration process unlesss you're in tow/haul...what I believe happens then is after a brake application and decelleration, the tranny will downshift through every gear (at a certain speed as you stated). It comes in handy when slowing a load.

BigGunZ

I think T/H works slightly between the 05's and 06's as well.

BigGunZ

Here's a pretty good description from the service manual...

OPERATION
The application of each driving or holding component is controlled by the valve body based upon the manual lever position, throttle pressure, and governor pressure. The governor pressure is a variable pressure input to the valve body and is one of the signals that a shift is necessary. First through fourth gear are obtained by selectively applying and releasing the different clutches and bands. Engine power is thereby routed to the various planetary gear assemblies which combine with the overrunning clutch assemblies to generate the different gear ratios. The torque converter clutch is hydraulically applied and is released when fluid is vented from the hydraulic
circuit by the torque converter control (TCC) solenoid on the valve body. The torque converter clutch is controlled by the Powertrain Control Module (PCM). The torque converter clutch engages in fourth gear, and in third gear under various conditions, such as when the O/D switch is OFF, when the vehicle is cruising on a level surface after the vehicle has warmed up. The torque converter clutch can also be engaged in the MANUAL SECOND gear position if high transmission temperatures are sensed by the PCM. The torque converter clutch will disengage momentarily when an increase in engine load is sensed by the PCM, such as when the vehicle begins to go uphill or the throttle pressure is increased. The torque converter clutch feature increases fuel economy and reduces the transmission fluid temperature. Since the overdrive clutch is applied in fourth gear only and the direct clutch is applied in all ranges except fourth gear, the transmission operation for park, neutral, and first through third gear will be described first. Once these powerflows are described, the third to fourth shift sequence will be described.

bigdav160

I've done a little reading on the "tow-haul" mode and came up with four things it does:

Raises line pressure in the transmission to prevent clutches and bands from slipping.

Modifies shift timing towards better performance not economy.

Turns "on" the lock-up clutch in the torque converter earlier to reduce transmission heat.

Turns "on" bands and clutches that are normally only used in the "manual ranges", ie D1, D2, D, to provide "engine braking" on decelleration.

trik396

I drive in tow/haul all the time, whether I'm loaded down or not. I was told it'll help the trans live longer. Don't know for sure, but it makes sense to me.

Herrin811

Thats no lie....On my '06, T/H provides a huge amount of engine braking....I dont notice alot of difference accelerating or cruising, except firmer shifts....Sounds alot like a 6-speed when decelerating

bluesurf

I think there is a big difference between the 05 and 06. I have to say I cannot feel the tc lock up in 3rd when going downhill or coming to a stop, although I do feel the tranny shift dow which is nice but I have yet to feel any sort of engine braking. I normally tow 10-12k a few times a week. The reason I ask is if mine is not corectly doing this or the 06 is better at it can I have the computer reflashed to do so. I dont want to add some sort of t/c lockup if the tranny is capable stock. Warranty wise. Big gunz thanks for the info. if anybody has an 05 and experiences what herrin is talking about please let me know. Maybe the 06 does it better. Thanks everone

v8440

As a side note, I would like to see something (preferably a plug in box rather than a computer reflash) that would modify when the converter clutch locks, as a fuel economy improver. Locking it under light load in the lower gears, and locking it earlier in 4th gear, would certainly improve in-town economy over the way it acts from the factory. Stock, they just rev up to about 1800 rpm and just kinda sit there, making heat instead of forward motion. That aggravates the hell out of me. If someone would make a box of some sort that would plug in to the wire harness somewhere, I'd buy one quick. I don't want a downloader, to avoid footprints in the computer.