Tow/ Haul mode...

[MiSdIrEcTeD_1]

OK... Basically it all boils down to that I want to know precisely every electronic(obviously), AND mechanical functions that take place when in Tow/ Haul...Anyone got any Tech-links or other info???

[hosspuller]

I got this a while back .. You might be interested..

Tow/haul

The 1000 Series features a 12-inch torque converter equipped with an electronically controlled, hydraulically actuated, converter clutch. The (TCM) Transmission Control Module selects the gear for each drive range and engages the torque converter lockup. This is important: the TCM controls BOTH gear selection and torque converter lockup. It is NOT controlled directly by the column gear selector lever or the Tow/Haul mode button. The reason this is important is because you are not controlling single variables when you make input selections with these controls. You are changing several things at the same time. So let's look at what these inputs cause the TCM to do.

The gear selection (D, 3, 2, 1) input changes the shift point and the high gear as anyone familiar with an automatic transmission should be familiar, but it is further affected by the mode. The 1000 Series employs two modes of operation for GMC and Chevy trucks: Normal Mode When the truck is being used for normal day-to-day driving, and Tow/Haul Mode. Tow/haul mode is available for when the truck is loaded (a button on the end of the gearshift lever activates it).

The two modes are differentiated by three primary functions:

1. Torque Converter Clutch lockup

2. Grade Braking

3. Shift Stabilization

Although the second and third, Grade Braking and Shift Stabilization, interact with gear selection, these three functions comprise the difference between normal and Tow/Haul mode and so should not be confused with the gear selection alone. Let's look at the three functions:

TCC

In normal mode, the TCC (torque converter clutch) is locked up in 4th and 5th gear. This provides for smoother up and downshifting when unloaded or with light loads, provides better fuel economy, and still provides for effective lockup under the higher loads of the upper gears (4 and 5). This is the best mode when the truck is at less than 75% of the GCWR.

In the Tow/Haul mode, the TCC is locked up in 2nd, 3rd, 4th, and 5th gears. Allison did this to avoid heat build up generated by a slipping TCC under heavy loads. This can occur when the vehicle and trailer are over 75% of the GCWR or under certain conditions such as frequent stop and go or steep hills.

Engine Grade Braking

Engine Grade-braking helps the driver slow the vehicle and avoid excessive use of the brakes. For example, when drivers carrying heavy loads encounter a steep hill, they can manually shift into a lower gear for added engine braking to slow the truck. The 1000 Series collects operating data, including how long the driver's foot has been on the brake, vehicle speed, gear currently engaged, etc., and uses it to calculate shift parameters. At a certain threshold, the TCM of the 1000 Series will cause the transmission to downshift without the driver having to move the gear lever. Manual range selection is still available to the driver. Again, in the Normal mode, it will shift down from 5th to 4th. In the Tow / Haul mode, it will perform multiple downshifts from 5th to 4th, then from 4th to 3rd, using steadily lower gears to slow the truck.

Shift Stabilization

Shift Stabilization uses the same type of advanced logic with input from the throttle position sensor, engine speed, and other factors. This feature detects and overcomes "shift busyness" that might be found in mountainous or hilly terrain. Algorithms housed in the TCM analyze the conditions, and when the parameters are satisfied it maintains the transmission in the lower gear for optimal performance. In Tow/Haul mode. the stabilizing effect this has makes driving a loaded vehicle considerably more comfortable.

As you can see, with the Tow/Haul mode, you are doing much more than telling the TCM to select a specific gear. The mode affects TCC lockup, the Engine Grade Braking program, and Shift Stabilization.

[MiSdIrEcTeD_1]

I got this a while back .. You might be interested..

Thats precisely what I was looking for.. Thanks a lot, bro...

[Kania2k1]

But, is it bad to drive in Tow/Haul mode when not towing or hauling anything?  I kinda like the exhaust note it makes

[bobc]

Isn't this write up about the Allison trans?  I've never heard of a 5th gear in a 4L60E, or 4L80E.  Cool write up however.  

 

My understanding is that the tow/haul alters shift points and raises line pressure for 1-2, 2-3 shifts.  It must crank up the TCC pressure to avoid slippage Which I personal think is a GREAT idea for any situation.  I don't like the shift points in tow/haul but the shift quality is close to the way I want it to be.  Mushy shifts suck big time, not to mention guarantees a tranny rebuild long before it should be needed.  Running in D (overdrive) is not doing the tranny any good around town either.  I always drive in 3rd unless on the freeway.

 

later

bobc

[Kania2k1]

Same here Bob.  Try it with tow/haul in 3rd, if ya have a louder exhaust, nice snap to the exhaust.    :thumb:

[maggot]

OK Now I am confused. I have the L485E, I have not noticed an OD towing or driving. Once up to speed putting the thing in tow haul does not effect PRMs. Only thing I notice is the shif points and the firmness of the shift. I have been told the L485 is a 4 speed tranny. No od. D is 4th gear. Maybe my tranny is not working corrrect.  My situation is this towing at 65 MpH I am in D at 2200-2500 RPM in TH mode, push the button my RPMs do not change. In fact when running across the rolling hills of KY I run out of tow haul mode because it downshifts too much and drives me nuts. My tranny temp stays well below the motor temp. In my opinion the TH thing is(let the flames begin) a gimmick. Maybe the ALly does different stuff but  to me in the 485 TH is not all that big of a deal an is not worth the extra money.

[MiSdIrEcTeD_1]

I have been told the L485 is a 4 speed tranny. No od. D is 4th gear. Maybe my tranny is not working corrrect.

It is a 4 spd... The Allison is the 5... Im still confused as to what your problem is... ???

[bobc]

Hey maggot...  pokin the tow/haul at cruise will not change anything, or rather it won't affect rpm.  It is altering line pressure and shift points.  If anything it's tightening up the TCC so it doesn't slip.  Also it may drop out of OD under lighter throttle application or hill loading.

 

The 4L60E, 45L80E, 4L85E are all 4 speed trannies.  85E is the most current HD version if I remember correctly.   Regardless 4th is OD.  Can't be turning just over 2200rpm at 65 without a real tall axle gear.  (my '66 dodge cop car had a 2.73 rear and turned 2000 at 65mph.) 3rd gear is 1:1 and is the recommended gear to use if you are towing anything of substance.  OD is not a good choice for towing, not unless you like rebuilding transmissions.

 

Try putting your truck in Tow/Haul around town, you will see the shifts happen later and you'll feel a more positive shift.   For example, the trans will stay in 2nd well over 30mph.  Normally I see 3rd by about 30 around town.  You won't hurt anything doing this without a trailer.  Like I said in another post, I drive in 3rd around town becuase if anything it avoids lugging the motor (potentially contributing to carbon build up???).  But mainly becuase the truck is more responsive and I don't have to call ahead when I want to accelerate.  

 

later,

bobc

[bobc]

Same here Bob.  Try it with tow/haul in 3rd, if ya have a louder exhaust, nice snap to the exhaust.    :thumb:

Agreed.  I have a flomaster setup and it's definately more talkative.  Has a nice burble under decel.   If I really want to get up and go this is definately the combo.  Better yet, manual shifting where you can hold 1st and 2nd as long as necessary to get the job done... like tossin a little humble pie at the new GT mustangs...  :thumb:

 

later,

bobc

[Kania2k1]

WURD American Thunder?  That's what I've got, took the tips that the setup came with off, couldn't get them to look straight, now it dumps after the axel.  With the tonneau on, it's a little bit louder in the cab.  NICE  I do like tooling along at about 45 in 3rd and popping the gas and feeling it immediately instead of a hesitation and downshift.

[maggot]

In my opinion  speaking from my 485E, I think the TH button is a gimmick and a tranny should not need some button to make it shift correctly. It should shift correctly with out shift kits or a button. The 400Turbo would be better in these trucks. It shifted great stock, handled as much torque as the Duramax puts out.

[MiSdIrEcTeD_1]

In my opinion  speaking from my 485E, I think the TH button is a gimmick and a tranny should not need some button to make it shift correctly. It should shift correctly with out shift kits or a button.

Do you realize how many people would complain about the way it shifted if it was a TH type shift all the time..? People like smooth quiet shifting; TH is great for towing, but not everybody pulls anything... Thats why its there to toggle on and off for those who do... :thumb:

[maggot]

Yep, most people who buy pick up trucks now a days wants a car and most trucks will never haul anything heavier than a soccer ball. I have to agree. How about this, on the HDs it could be backward, have it change gears proper by default and have a button that smoths it out.

[TarheelZ]

Do any of you have experience with valve body upgrades?  I have a JET kit in my ZR2 and I'm planning to put one in my Sierra next.  I've been VERY pleased with the way the 4L60-E shifts in my ZR2.  I want my Sierra to shift this way, too!