Towing Transmission Question

[Airman68]

So I have a 2008 Yukon XL with the 6spd transmission. just bought June 2022. Towed my #3500 lb boat last summer with little issues. This winter I was towing a 2 place enclosed snowmobile trailer with 2 sleds on a fairly flat road. It seemed to me that even in tow mode, the thing shifted up and down more than I would think. I was under the impression that in tow/haul, it kept the truck in a lower gear to stop a lot of that. Is that right? Seems with a 2000lb trailer, this should have been a cakewalk. I't just seemed to struggle. My son in law towed the same trasiler with his Dodge 1500 without trouble. Any suggestions?

 

[Geotrash]

So I have a 2008 Yukon XL with the 6spd transmission. just bought June 2022. Towed my #3500 lb boat last summer with little issues. This winter I was towing a 2 place enclosed snowmobile trailer with 2 sleds on a fairly flat road. It seemed to me that even in tow mode, the thing shifted up and down more than I would think. I was under the impression that in tow/haul, it kept the truck in a lower gear to stop a lot of that. Is that right? Seems with a 2000lb trailer, this should have been a cakewalk. I't just seemed to struggle. My son in law towed the same trasiler with his Dodge 1500 without trouble. Any suggestions?

An enclosed trailer will haul very differently than a boat because it's effectively a large drag chute.

Tow/haul mode will generally keep the transmission in a lower gear for longer, but it will still make it to 6th sometimes and seem to hunt between 5th and 6th as you go up and down hills so small that they're barely perceptible. When I tow I set the gear selector to M and then use the buttons on the shifter to select the maximum gear that I want the truck to use given the terrain. Most of the time when I'm pulling our 7500 lb camper on the highway on flat ground, that's 5th. But when I get into rolling hill country, I'll sometimes limit it to 4th to minimize the amount of shifting it needs to do. This is true for both of our Yukon XL Denalis.

 

[swathdiver]

So I have a 2008 Yukon XL with the 6spd transmission. just bought June 2022. Towed my #3500 lb boat last summer with little issues. This winter I was towing a 2 place enclosed snowmobile trailer with 2 sleds on a fairly flat road. It seemed to me that even in tow mode, the thing shifted up and down more than I would think. I was under the impression that in tow/haul, it kept the truck in a lower gear to stop a lot of that. Is that right? Seems with a 2000lb trailer, this should have been a cakewalk. I't just seemed to struggle. My son in law towed the same trasiler with his Dodge 1500 without trouble. Any suggestions?

Is this a Denali or an SLT? 2008 SLTs had a 4-speed transmission (M30), the Denalis had the 6-speed (MYC). How many miles are on the engine?

Either way, with a light load it ought to tow just fine, the 4-speed trucks were equipped with 3.73 (GT4) or 4.10 (GT5) gears.

 

[Airman68]

Ok, yeah mine it a SLT, not Denali. For some reason I thought it was the 6spd, must have misread that somewhere. Got 190K on the engine and I have the AFM disabled. On my last Silverado with the 4spd, it seemed when I put it in tow/haul, it mostly stayed out of OD unless it was going downhill.

 

[B-train]

With the 4 speed trans, you may just want to lock it in 3rd. Hunting for gears adds more stress and heat. Extra RPM won't hurt a thing

 

[Jhwhite05]

An enclosed trailer will haul very differently than a boat because it's effectively a large drag chute.

Tow/haul mode will generally keep the transmission in a lower gear for longer, but it will still make it to 6th sometimes and seem to hunt between 5th and 6th as you go up and down hills so small that they're barely perceptible. When I tow I set the gear selector to M and then use the buttons on the shifter to select the maximum gear that I want the truck to use given the terrain. Most of the time when I'm pulling our 7500 lb camper on the highway on flat ground, that's 5th. But when I get into rolling hill country, I'll sometimes limit it to 4th to minimize the amount of shifting it needs to do. This is true for both of our Yukon XL Denalis.

That’s really helpful. Thanks for explaining that! I’ve wondered how to best use tow/haul mode

 

[swathdiver]

Ok, yeah mine it a SLT, not Denali. For some reason I thought it was the 6spd, must have misread that somewhere. Got 190K on the engine and I have the AFM disabled. On my last Silverado with the 4spd, it seemed when I put it in tow/haul, it mostly stayed out of OD unless it was going downhill.

Well, the Yukon weighs at least 500 pounds more than the Silverado, so the load will be more and if there is a gearing difference between the two, take that into account as well. Tow/Haul really only provides a benefit when you are at 75% of the GCWR. If the trans can't make up its mind, let it run in third gear, better for it anyway.

 

[intheburbs]

You never want to tow in OD with a GM 4-speed.

In third gear, you're at a 1:1 ratio, so the transmission is simply a pass-through. In OD, things are different. The design of the 4L65 transmission dates all the way back to the 70s and the original 4-speed where GM simply added on a set of small planetary gears to get that overdrive ratio. So when you're towing in fourth you're doing two bad things:
1) Your routing all the engine power through that small planetary gearset.
2) You're asking that same gearset to multiply the torque of the engine, because of the 0.696:1 ratio

You're putting maximum stress on the weakest part of the transmission. Sound like a recipe for durability and reliability?

 

[Marky Dissod]

Hope you got 4.10 with that 4L60E.

I'd only use 'OD' while cruising or decelerating on level ground or on a downhill.
For ANY acceleration whatsoever, I'd put the shifter back in 'D'.

Frankly, I'd go one step further and get tuned. Nevermind the various engine improvements.
The 1st last and most important reasons to get tuned are to improve the transmission shift tableS.
In your case, I'd ask the tuner to make the Tow / Haul shift map 'even Towier / Haulier'.
Tell the tuner you're towing a heavy object with lots of aero drag.
Even if the tuner is not smart enough to improve the line pressure tables, just by improving the shift tables, the transmission will last longer, especially when towing / hauling.

Also, if you are actually towing something with lots of aero drag, you may want to look into DIY vortex generators.
AirTabs are a decent value @ $3 apiece shipped, but you can spend a whole hell of a lot less, get nearly as much benefit, and pay yourself back quicker.

 

[NickTransmissions]

You never want to tow in OD with a GM 4-speed.

In third gear, you're at a 1:1 ratio, so the transmission is simply a pass-through. In OD, things are different. The design of the 4L65 transmission dates all the way back to the 70s and the original 4-speed where GM simply added on a set of small planetary gears to get that overdrive ratio. So when you're towing in fourth you're doing two bad things:
1) Your routing all the engine power through that small planetary gearset.
2) You're asking that same gearset to multiply the torque of the engine, because of the 0.696:1 ratio

You're putting maximum stress on the weakest part of the transmission. Sound like a recipe for durability and reliability?

Not to mention the stress on the 3/4 clutch pack and band when towing in OD. Those two applied elements will stress and fail before any of the hard parts unless the engine’s putting out gobs of torque. The 65/70es can handle towing/HD use alot better than the base M30 4l60e or 700r4 (82-93) given their 7-clutch 3-4 pack, better valve body hydraulic calibration, five pinion planets, induction hardend input shaft and, in the case of the 4l70, the induction hardened reaction shaft but i wouldn’t recommend it on any kind of regular basis unless a billet 4th gear servo, kevlar or red wide 2-4 band and upgraded pump hydraulics have been installed, along with an HD tune, deep pan and big cooler…