Jump to content

Downshifting while slowing down in Tow/Haul Mode

Lenny_B

By Lenny_B
in 6.6L Gas V8 (L8T)

 Share

Recommended Posts

Another JR Senior Enthusiast

Another JR

Posted
Posted

By “aggressive” I think the OP means the selection of a gear that results in very high rpm as opposed to the characteristics of the actual shift from gear to gear. That’s what I was commenting on, at least. It actually shifts very smoothly. I just don’t like descending with the engine revving at over 5k. The highest rpms my truck has seen in its 6500 mile life were the one time I put it in tow haul on a moderately steep mile half mile hill near my house just to try it. 

  • Like 1
Ray Pickle Enthusiast

Ray Pickle

Posted
Posted
8 hours ago, Another JR said:

By “aggressive” I think the OP means the selection of a gear that results in very high rpm as opposed to the characteristics of the actual shift from gear to gear. That’s what I was commenting on, at least. It actually shifts very smoothly. I just don’t like descending with the engine revving at over 5k. The highest rpms my truck has seen in its 6500 mile life were the one time I put it in tow haul on a moderately steep mile half mile hill near my house just to try it. 

I don't recall my truck ever downshifting while in tow haul to 5k.  Frankly I don't think it downshifts far enough at hwy speeds during deep descends to maintain desired speed. Example, if I have crested a hill and it is 5-6% down for the next mile plus and I am at 65mph the truck only downshifts to 4th gear in an attempt to hold speed. Often speed increases and a downshift to 3rd is no longer an option even on manual mode. If I am concerned about the length and steepness of the decline I typically slow to about 50 or 55 and manual go to 3rd gear beginning descent. Rpm's are higher but truck is in control of trailer and brakes are cool if needed.

  • 3 weeks later...
Sierra Jon Enthusiast

Sierra Jon

Posted
Posted

I regularly tow a TT that weighs 10k. Personally, the downshift works perfectly. I generally tap the brake when I know I am going to slow down and she immediately downshifts. It's like we're dancing. Haha

 

Also, I may or may not have used it when putting around town and that downshift gets my magnaflow to sputter a teeny bit when you coast down to 20mph. Music to my ears. 🎶 

 

  • 3 months later...
Dr1ft3r Enthusiast

Dr1ft3r

Posted
Posted (edited)
On 9/15/2022 at 9:23 AM, Ray Pickle said:

I don't recall my truck ever downshifting while in tow haul to 5k.  Frankly I don't think it downshifts far enough at hwy speeds during deep descends to maintain desired speed. Example, if I have crested a hill and it is 5-6% down for the next mile plus and I am at 65mph the truck only downshifts to 4th gear in an attempt to hold speed. Often speed increases and a downshift to 3rd is no longer an option even on manual mode. If I am concerned about the length and steepness of the decline I typically slow to about 50 or 55 and manual go to 3rd gear beginning descent. Rpm's are higher but truck is in control of trailer and brakes are cool if needed.

 

This sounds exactly like my recent situation while cruising down a 7% grade for 10 miles. My CC was set at 65 mph and I had to keep tapping the brakes because I kept creeping up to 70+ mph. I wasn't hauling and wasn't using tow mode. I think it was downshifting but it wasn't enough to keep my truck from accelerating by about 1 mph per 5 seconds. My truck is fat though with a curb weight of 7,450, lol.

 

As for the OP's issue: the downshift may seem aggressive for putting around town on flat land with a mild load. But you'll be thankful for that aggressiveness on a very steep grade with a full load. If it's too aggressive then just don't use it. You'll be using the sand pits if you need it and you don't have it.

Edited by Dr1ft3r
  • Like 1
swathdiver Senior Enthusiast

swathdiver

Posted
Posted
On 9/3/2022 at 9:36 AM, Epsilon Plus said:

I wouldn't be surprised if GM retuned it to be super aggressive after the crap showing in 2020 on TFL's Ike Gauntlet. The truck barely downshifted at all for them. My 2022 will drop gears like a professional trucker trying to brake an 80,000lb load (not a complaint, works great).

TFL doesn't use the cruise control while running the test downhill.

NaturallyAspirated Enthusiast

NaturallyAspirated

Posted
Posted

FWIW my truck is very unpredictable on the downhills. I’d like to better understand how GM’s CC is Supposed-to behave…

 

Ya at times it makes me feel like a boss trucker but other times I end up going 80 downhill like the OP.

swathdiver Senior Enthusiast

swathdiver

Posted
Posted
7 hours ago, NaturallyAspirated said:

FWIW my truck is very unpredictable on the downhills. I’d like to better understand how GM’s CC is Supposed-to behave…

 

Ya at times it makes me feel like a boss trucker but other times I end up going 80 downhill like the OP.

What year is it?  I wonder if it's described better in the Upfitter Manuals?

XY74 Enthusiast

XY74

Posted
Posted

I have also read the owners manual and am fine with their advice to use tow haul when loaded at 75%+, and not use it with less.  I almost never use it.  (disclaimer, I have a diesel with the 10 spd)  What do you feel tow haul mode is giving you that you would miss aside from the aggressive downshifts when slowing?  I wouldn't consider a 5000 lb boat to be too serious of a load for these trucks.  

  • Like 1

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Latest Articles

  • Posts

    • newdude
      Gasser Subforum Has Been Quiet - - So, Regenerative Braking and Using L10

      By newdude · Posted

      No such thing as regenerative braking on a pure ICE vehicle.     Regenerative braking is the re-capture of energy from electric motors and stores it in the battery pack.  So hybrids, PHEV and EVs have regenerative braking.     What you are seeing is the charging system changing modes is all.  Its likely entering charge mode for some sort of reason is all.  All of the charging modes will be listed below.   As for L10 vs D.  L10 turns off automatic grade braking.  L10 puts you in control of grade downshifts where in D it will automatically do it based on brake pedal position and other factors.  Otherwise L10 and D drive exactly the same aside from that one aspect.    Battery Sulfation Mode The BCM will enter this mode when the interpreted Generator output voltage is less than 13.2 V for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2–3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.   Charge Mode The BCM will enter Charge Mode when ever one of the following conditions are met:   Windshield wipers are ON for more than 3 s. Climate Control Voltage Boost Mode Request is true, as sensed by the HVAC control module via serial data. High speed cooling fan, rear defogger, and HVAC high speed blower operation can cause the BCM to enter the Charge Mode. The estimated battery temperature is less than 0°C (32°F). Battery State of Charge is less than 80%. Vehicle speed is greater than 145 km/h (90 mph) A current sensor malfunction exists. System voltage is determined to be below 12.56 V When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9–15.5 V, depending on the battery state of charge and estimated battery temperature.   Fuel Economy Mode The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 A and greater than −8 A, and the battery state-of-charge is greater than or equal to 80%. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5–13.1 V. When fuel economy mode is active, the generator is not charging, only maintaining open circuit battery voltage. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.   Headlamp Mode The BCM will enter Headlamp Mode when ever the head lamps are ON (high or low beams). Voltage will be regulated between 13.9–14.5 V.   Start Up Mode When the engine is started the BCM sets a targeted generator output voltage of 14.5 V for 30 s.   Tow/Haul Mode (if applicable) Pressing the Tow/Haul Mode button located on the center stack, the vehicle system voltage is raised and the remote (non-vehicle) battery will be charged. Having the headlamps on will raise the system voltage and if the Tow/Haul button is applied it will not serve any purpose. The voltage is regulated between 13.9-14.5 V.      
    • jaszr2
      Active Grille Delete

      By jaszr2 · Posted

      Hello from Australia Just sharing that there is now a way to delete the active shutters entirely with just a plug in module. Opens up tons of room to light bars etc.
    • jake111
      Gasser Subforum Has Been Quiet - - So, Regenerative Braking and Using L10

      By jake111 · Posted

      I have an observation and a question... 1) I watch the voltage closely because I have had to dial in the cut-in/cut-out voltages of the battery separator to my camper.  The "smart" charging drives me nuts.  Anyway, I noticed that when coasting for a while, and especially if lightly using the brakes (though not necessary), the voltage goes up from mid/high-13 volts to mid/high-14 volts.  Then it drops back down after stopping or going again.  Consistently!   The only explanation I can come up with is REGENERATIVE BRAKING!  Well, maybe that's a little bit of an exaggeration, but it's certainly free extra battery charging.   2) Driving on mountain roads I will use L and vary the max gear.  Things straighten out and I end up in L10.  Sometimes I leave it there for a while.  Is there any difference between L10 and D?   
    • devonthegreat
      anyone interested in a 2002 Chevy Silverado 4x4 parts truck NYC

      By devonthegreat · Posted

      **SOLD** Please end or delete post. thank you
    • PBNB
      Tire pressure for 37s

      By PBNB · Posted

      Do you think this width might affect the chalk test with a higher pressure closer to 65psi? I think lowering the pressure makes sense to get the tread to lay flatter

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...