Question for GM 6.6 Diesel Owners with 10 speed Allison

[COGrandDes]

I haven’t figured this out yet, so I’ll ask the group. Ford owners, if you experience this, feel free to chime in.

When descending a hill in tow/haul mode, as I get on the brake, the tranny will downshift to help hold back the truck. If I continue on the brake, it will continue to downshift to the point the engine may bump up to 3000+ rpm. This is all without the exhaust brake on. On a lot of gradual short descents, I don’t want it to downshift that much. One gear would be plenty. The only way I’ve figured out how to defeat this is take it out of tow/haul mode.

Anybody have any thoughts?

When I start my truck and hook to the camper, I enable the exhaust brake for my whole trip. I never use the tow/haul mode. The exhaust brake will do what's needed and in combination with the cruise will keep things where they need to be on most hills. This is how I roll in CO where I live and with all the mountains. If you don't want to use the cruise coming down the hills...then just tap the brake to enable the exhaust brake and downshifts together. One or two taps of the brakes does it for me...no need to ride them down the hills. If I start slowing down too much...I add throttle till I get to the speed I want. All while the exhaust brake is enabled and doing the brunt of the work!

[Hoopy Frood]

When I start my truck and hook to the camper, I enable the exhaust brake for my whole trip. I never use the tow/haul mode. The exhaust brake will do what's needed and in combination with the cruise will keep things where they need to be on most hills. This is how I roll in CO where I live and with all the mountains. If you don't want to use the cruise coming down the hills...then just tap the brake to enable the exhaust brake and downshifts together. One or two taps of the brakes does it for me...no need to ride them down the hills. If I start slowing down too much...I add throttle till I get to the speed I want. All while the exhaust brake is enabled and doing the brunt of the work!

Just curious, what don't you like about the tow haul mode?

[Mannyjt]

Tow/Haul+EB the whole trip. Saves your brakes and helps to maintain speeds both on downhill grades and in cruise control.

I also use it while daily driving to make braking easier.

Owners manual says to engage it when towing or when using cruise control. When in tow/haul its much more aggressive.

I guess I'm confused on what the purpose behind not using it would be? It's designed to operate with it.

[COGrandDes]

Just curious, what don't you like about the tow haul mode?

On my 2017, I didn't like the way the TH shifted and it was too aggressive. On my new 2022, I use the Tow mode as it's the only way to get all the engine torque applied to first gear when pulling. I was confusing my previous 2008 and 2017 with my 2022. On the 2022, I do switch to tow mode and enable the EB from the start. Tow mode is mostly useful for pulling the loads from a dead stop rather than highway driving unless you are pulling allot of long hills. I keep an eye on trans temps and converter lockup to ensure the trans is not generating too much heat. I would recommend enabling it and using the EB together as others have noted especially for the new trucks. Fuel economy might likely suffer a bit but if you bought a diesel for a reason...you will likely want all the torque, all the gearing, and firmer shifts by the line pressure changes.

[Hoopy Frood]

On my 2017, I didn't like the way the TH shifted and it was too aggressive. On my new 2022, I use the Tow mode as it's the only way to get all the engine torque applied to first gear when pulling. I was confusing my previous 2008 and 2017 with my 2022. On the 2022, I do switch to tow mode and enable the EB from the start. Tow mode is mostly useful for pulling the loads from a dead stop rather than highway driving unless you are pulling allot of long hills. I keep an eye on trans temps and converter lockup to ensure the trans is not generating too much heat. I would recommend enabling it and using the EB together as others have noted especially for the new trucks. Fuel economy might likely suffer a bit but if you bought a diesel for a reason...you will likely want all the torque, all the gearing, and firmer shifts by the line pressure changes.

Gotcha, I always use the Tow Haul when pulling our trailer, and I do get curious why people wouldn't use it. It does make pulling a heavy load easier, albeit the shifts are sharper. Just as an aside, I do like the Aisin transmission on the Ram, I've pulled on hot days, uphill and down, and I've never seen the transmission temperature raise more than 3 degrees. Truly amazing compared to the old Dodge/Ram transmissions.

[LMagelitz]

Does it act differently if you have the exhaust brake engaged?

Didn’t try that.

[LMagelitz]

I don’t have the 10 speed, but my 6 speed Allison does the same thing. I use the exhaust brake which does minimize that. I prepare for a steep descent by getting to my speed before the downhill starts, that makes it much easier to maintain that speed without hitting the brake.

Bill

Ah, I haven’t tried it with the exhaust brake yet. Thanks!

[LMagelitz]

Thanks to all for the discussion, I really appreciate it!
I have some things to try now.
We’re going out west later this summer, so I’ll be going thru mountains for the first time with this rig.

[ajg617]

unless you are pulling allot of long hills.

Every direction I go seems to be uphill. I keep Tow Haul and EB Auto on unless a steep downhill grade is upcoming and I'll switch to EB Heavy before. I do not use CC as I found that the Aisin downshifts far too soon on an uphill. I'd rather drop a little speed and stay in the same gear than have to play with it to upshift on the next level or downhill. Ram's shift points are odd. If I get up to 67mph on level highway, it will drop into 6th which I can keep down to 59mph even slightly uphill. With TH on, it will not go into 6th until 67mph. With CC on, it will downshift at much lower boost with TH on in an uphill. I'm going to play with not using TH on next short run. Every time I shut down for fuel, TH is off but EB stays on when I restart. Thought that was odd since the trailer is still connected. I've forgotten to put TH back on again and have to say I liked the way TV pulled better. I dunno.

[FedMill]

Ford owner chipping in here...it has been a while since I've been in any significant hills or mountains. I want to say holding the break will only downshift once? I believe I have to lift my foot and brake again to get another down shift. If it is very steep downhill grade, I lock out the top couple gears.

The above true. I always run with exhaust brake on and in tow haul mode. (When towing) I will shift to manual when I feel the need to control what gear I want to be in, especially on steep grades. (Yes I know the tranny has a brain of its own but when I am running steep grades I want to be in control ) I have run many a steep mountains as an Rv Transporter and the above works Great for Me !!