Jump to content

Starting in 2nd gear when towing?

alkaspeltzar
 Share

Recommended Posts

alkaspeltzar Enthusiast

alkaspeltzar

Posted
Posted

2019 Silverado 1500 z71 with 8K miles, 3.23 rear, 8 speed.

 

Today I have towed about 8000lbs of cattle and trailer. I prior towed an old farmall tractor back.

 

Both times when towing over 6000lbs, I had the transmission in L6, tow haul mode. Sometimes when taking off from a stop, it almost felt like the truck started in 2nd, not dropping down the first. Would it do that? Or is the torque converter just being floated as RPM's rise, and possibly I am not feeling the shift from 1 to 2. This transmission is crazy smooth compared to my 6 speed.

 

Truck drives great otherwise. Ran it to town empty later, no issues.  Even ran it thru the Low mode gears, and it starts in first normally. Thought maybe this was towhaul mode trying to avoid unnecessary shifting if still rolling. Transmission running cool, never over 180 even with that load at 60-70 mph.

 

Thanks for sharing your experiences.

 

flyingfool Senior Enthusiast

flyingfool

Posted
Posted (edited)

you should data log the trans next time to confirm this is happening, i know HPtuners has all the PIDS to show you whats happening durring a logged capture of the operation. 180 F is a bit warm unless your going up grades.  but if its a lease truck no worries

Edited by flyingfool
Wintersun Enthusiast

Wintersun

Posted
Posted

180F degrees is on the low side even if not towing a heavy trailer. Tow/haul mode is recommended when the trailer and truck weight exceeds 75% of the trucks rated GCWR. Tow/haul mode will change shift points and also keep the torque converter locked longer on upshifts which is intended to minimize heat buildup with the transmission fluid. At 180 degrees this is hardly a concern. By the way the flash point with even cheap ATF is over 350 degrees. Using Range Selection mode disables Grade Braking and is not advisable with a heavy trailer.

alkaspeltzar Enthusiast

alkaspeltzar

Posted
  • Author
Posted
22 hours ago, Jav_eee said:

Just curious as to why you wouldn’t just put in in drive with tow haul?


Sent from my iPhone using Tapatalk Pro

Becuase id rather keep it in 5th when towing heavy loads. Sometimes it bounces back and forth between 5-6. 

  • Like 1
alkaspeltzar Enthusiast

alkaspeltzar

Posted
  • Author
Posted
3 hours ago, Wintersun said:

180F degrees is on the low side even if not towing a heavy trailer. Tow/haul mode is recommended when the trailer and truck weight exceeds 75% of the trucks rated GCWR. Tow/haul mode will change shift points and also keep the torque converter locked longer on upshifts which is intended to minimize heat buildup with the transmission fluid. At 180 degrees this is hardly a concern. By the way the flash point with even cheap ATF is over 350 degrees. Using Range Selection mode disables Grade Braking and is not advisable with a heavy trailer.

Didn't say temp was issue, just commenting truck stayed very cool compared to my 2010 or 2014

alkaspeltzar Enthusiast

alkaspeltzar

Posted
  • Author
Posted

I see if can pull it from Drive to Low mode when driving. If I take off next time when towing, I might try that as I'll be able to see what gear it's in.

 

Also I notice while driving it empty it hoops from 1-2 so quick and smoothly, and being the ratios are very close, I don't notice it. This is most likely the case when towing

Jav_eee Enthusiast

Jav_eee

Posted
Posted
Becuase id rather keep it in 5th when towing heavy loads. Sometimes it bounces back and forth between 5-6. 

Tow/haul is supposed to prevent that.


Sent from my iPhone using Tapatalk Pro
flyingfool Senior Enthusiast

flyingfool

Posted
Posted (edited)
17 hours ago, Wintersun said:

180F degrees is on the low side even if not towing a heavy trailer. Tow/haul mode is recommended when the trailer and truck weight exceeds 75% of the trucks rated GCWR. Tow/haul mode will change shift points and also keep the torque converter locked longer on upshifts which is intended to minimize heat buildup with the transmission fluid. At 180 degrees this is hardly a concern. By the way the flash point with even cheap ATF is over 350 degrees. Using Range Selection mode disables Grade Braking and is not advisable with a heavy trailer.

at 180F its not the oil having problems, its the TECM components, plastics and all the delicate rubber seals inside  that are effected by this temperature by oxidation and loss of plasticity in those components... tow haul just disconnects the clutches in the Torque converter and might boost line pressure to clutch packs while raising shift points

Edited by flyingfool
ullose272 Enthusiast

ullose272

Posted
Posted
at 180F its not the oil having problems, its the TECM components, plastics and all the delicate rubber seals inside  that are effected by this temperature by oxidation and loss of plasticity in those components... tow haul just disconnects the clutches in the Torque converter and might boost line pressure to clutch packs while raising shift points
206-215 is considered normal operation temp, modern transmissions usually have thermostats built into the system to keep them at this temperature

Sent from my SM-G973U using Tapatalk

  • 2 years later...
Traperkeeper80 New Member

Traperkeeper80

Posted
Posted

My 2023 2.7 is absolutely doing this while towing 6,000 lb camper. It even does it launching on the equivalent of a boat ramp incline, from a dead stop. 
 Who is the EPA idiot at GM that thinks a 2nd gear launch with 6K is the right programing?  You can easily tell this is hard as hell on the drive line components. I have to manually shift to low, then force it to 1st gear to take off. 

Gangly Senior Enthusiast

Gangly

Posted
Posted
On 5/23/2020 at 9:53 PM, flyingfool said:

you should data log the trans next time to confirm this is happening, i know HPtuners has all the PIDS to show you whats happening durring a logged capture of the operation. 180 F is a bit warm unless your going up grades.  but if its a lease truck no worries

180 is low, especially for towing with the 8 spd.  The transmission normally runs at 185 all day long with no load.  That transmission temperature is a good thing to see.

Gangly Senior Enthusiast

Gangly

Posted
Posted (edited)
On 5/25/2020 at 10:21 AM, flyingfool said:

at 180F its not the oil having problems, its the TECM components, plastics and all the delicate rubber seals inside  that are effected by this temperature by oxidation and loss of plasticity in those components... tow haul just disconnects the clutches in the Torque converter and might boost line pressure to clutch packs while raising shift points

These transmissions are designed to run at this temperature during daily driving duty.  There is a video of the GM engineer who helped design the transmission discussing operating temperatures and the design process of the transmission, and ideal temperatures when towing were low 200's with 185-190 being ideal operating temperatures during normal use.  Degradation to seals and increased wear to components didn't occur until prolonged exposure to the mid/high 200's

Edited by Gangly

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

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

      By Another JR · Posted

      Have considered installing a DC to DC charger in your camper to replace your isolator?  
    • newdude
      Gas fill door

      By newdude · Posted

      Common failure.  You need to replace the fuel door housing.   The painted cover transfers over to the new housing.  To remove the old one there is 4 spots where you poke the plastic to release it.  
    • 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?   

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...