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

    • Aimatdeer
      Ac not keeping up

      By Aimatdeer · Posted

      Anyone have any info about backorder time? It's classic 4th of July hot here in ohio.
    • Chuck FB
      Fluid Change Questions

      By Chuck FB · Posted

      There would be one way of determining the quality of the factory oil although probably more than a typical oil lab test, and that would be to draw out some oil from a new truck and send a sample to a lab that could do a more elaborate test of the oil. The issue with too little oil in the diff may not be the lack of lubrication of the diff bearings and gears themselves ( although a lack of oil volume for cooling ) but the wheel bearings because at some point the oil would be too low to properly get onto the spinning axle or fed along the axle tube. That was the claim by the local dealer from a couple of trucks in recent years that had the wheel bearings fail and they figured from lack of sufficient oil due to a severe underfilled diff and some of the bearing material made its way to the diff and it got damaged as well so the axle housings were just replaced on warranty. But your right that if the diff is over filled by whatever margin that it causes more churning of the oil than is desirable and that is no good either and can cause a pinion seal to leak. Also old oil I believe can tend to loose some of its properties like antifoaming and another good reason to change the diff oil every so often. 
    • Z45
      Fluid Change Questions

      By Z45 · Posted

      I would be surprised if the diff's were not filled (with the cheapest gear lube) at the axle factory before being shipped to GM.  If you ever watched them building trucks they install the axles and all suspension parts with the frame upside down and then turn it over before its time to install the engine.     Too much gear lube in a axle can be worse than not enough especially with a lower quality GL where is get whipped up with entrained air (foam)  weakening its ability to lubricate.        
    • MORSNO
      Oil Consumption

      By MORSNO · Posted

      This is the 6.6 gasser section of the forum, you should either delete or modify your previous post as it is misleading for anyone looking for factual information on their 6.6 gas engine.
    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      Well....I've done my first intake gasket. Probably wrong, but...we'll see?   Ultra black on the china walls and 1/4" up onto the sides of the intake gaskets. Permatex High Tack (couldn't find Gaskachinch) on the head side of the intake gasket. I read wrong and it says you're supposed to put it on the mating surface of the head, not the gasket. Hoping it's like a PB&J sandwich where it doesn't matter what side the PB goes on so long as there's jelly. That crap is messy/sticky and I got a dab or two on the intake port openings, tried to wipe it off. Hopefully it won't be a big deal and will only aid in sealing.   Per instructions I left the intake (top side) of the gasket dry except for a light smear of RTV around the coolant ports. Wiggling the intake in there was a bear but I had help to free me of surrounding wiring/stuff but I was basically able to set it straight down lined up with the bolt holes.   I did not think to wait until the RTV skinned over but there probably was 5-10 minutes while it sat before installing the intake.   Bolts finger tight first. Then, followed the Chilton's manual pattern to snug them to 15 lb-ft.   Waited a little over an hour, and then did the final torque in sequence again to 35 lb-ft.   Yesterday I replaced the fuel pressure regulator and got my new "nut and bolt kit" (fuel lines) installed. Damn GM used security torx on the spider, which I don't have, so I got scammed at the local HW store for an off-brand security Torx bit set.   The new driver's door mirror arrived yesterday, so, there's a chance this thing could be running and road legal tomorrow? I don't want to get my hopes up.   This will be my first time stabbing a distributor, too. Although, lucky me, someone else marked the old distributor for removal previously, I did see that. (Someone's been here before!!). Engine is still at TDC so it *should* be just a matter of transferring the mark to the new dizzy and rotating it into place.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...