DMax/Allison - No overdrive with tow/haul mode

[JyRO]

Howdy!



I was at the Detroit Auto Show yesterday. I went over and looked at the Chevy area. I looked at a truck with the DMax.



On the (automatic) shifter lever, it had a symbol on it that was trying to depict not using OD when in the tow/haul mode.



The symbol showed (from the end of the lever toward the steering column) a) an arrow pointing in the direction of the column (designating pushing the tow/haul button), b) a trailer (for when towing), c) an OD symbol (with the D inside the O) and the diagonal slash through the OD symbol (designating to not use OD).



At first I thought that the transmission may not be an Allison, so I looked under the truck and the transmission pan said "ALLISON. "



What I don't know is if pushing the tow/haul mode electronically locks out the OD, or if the lever would have to be moved out of the OD position.



The point is, I thought the Allison was supposed to be able to handle towing in OD. But now the factory is (at least) recommending NOT towing in OD, possibly even forcing it out of OD by using the tow/haul feature. I wonder if Chevy's having troubles with the Allison breaking when towing (in OD)?



Has anyone else heard of this or have more info?



Thanks.



- JyRO

 

[MABurns]

In Tow / haul mode the Allison is still a 5 speed and uses OD.

It only alters the shift points. It keeps the RPMs higher before shifting, and also down shifts out of OD quicker (my observations).



It also activates the grade braking on hills.

 

[JyRO]

I know what the point of tow/haul mode is...

MABurns - does yours have this symbol? Or does yours say "Tow/Haul" ?



If yours doesn't have it (which I suspect yours says "Tow/Haul"), then this is new. Which means Chevy may have made a change in the Allison's programming. So I return with my observation in my original post.



- JyRO

 

[MABurns]

Mine simply says Tow/haul mode. My neighbor has a 2003, I'll ask him, and see what it says in his owners manual.



I down loaded the Allison manual (1000 series) from their website and it states to use OD and allow the transmission to downshift also.



But it may have changed for 03 and I'll check.

 

[Joel Richards]

You DMax guys may want to check out the available options for the Allison from ATS. High HP applications can cause 5th gear slippage after time, and from what I hear, towing really heavy loads can do the same even with tow/haul mode active.



I'll let you read there for more information... It should answer all of your Allison questions about towing.



HTH



-joel

 

[JakeGMCHD]

JyRO



GM added a OD lockout for when the trans is shifting between drive and over drive. The 01 and 02 trucks can have the TCM reprogrammed and add a momentary switch to have this option. On some grades the trans seems to hunt. It will also help raise the rpms when EGTs are getting high.

 

[JyRO]

Latest info...

I just found out that the button is a combo. 1 quick push for tow/haul on & off. 1 long push of 3 seconds to lock-out or turn on the OD. It seems to make some since with the symbol, once you have this info.



- JyRO