Allison Question

[TPB]

Howdy!

 

I'm fairly new to this site. After much research & reading I just traded my 2001 Chevy 2500HD Crew Cab 6.0 for this new 2005 GMC Sierra 2500HD with the Duramax & Allison. So far I'm extremely pleased. I tow a 9,000lb fifth wheel camper & a 2,500lb boat behind the fifth wheel, & it was a bit much for the 6.0.

 

My question is:

 

When I'm driving down the highway & move the shift lever from OD (5th) to the "3" position, the truck shifts down two gears - evidently into 3rd gear, & skips 4th gear. It appears the only way to manually shift into 4th is to disable the OD. Is this correct?

 

Todd

[496 CUBIC INCHES]

My question is why do you want to manually shift into 3rd anyways?

[TPB]

I didn't want to shift into 3rd, but into 4th - just down one gear from overdrive. It automatically shifted me down two gears into 3rd. It's not a big deal - if I need to tow in 4th, I'll just disable OD.

[Shooter_va]

A friend of mine has the same set-up, when he pushes and holds the tow/haul mode button on the shift lever for a few seconds, this will lock out the overdrive.

[MS3DALE]

Yes,just push and hold the TOW/HAUL button and it will disable OD and put you in 4th gear,it mentions it in the owners manual.

[496 CUBIC INCHES]

OK then....why did you want to downshift into fourth? Just so you'll be out of O/D? I guess I don't see why you needed to to be in fourth.

[KyleBst264]

Press the tow/haul button quickly to disable/enable tow/haul mode.

 

Press and hold the tow/haul button to disable/enable overdrive. With O/D off, it will not go beyond 4'th.

 

You can run tow/haul on and overdrive off simulataneously and one without the other.

 

Also, if you want downshifting action, put it in tow/haul mode and take your foot off the throttle and your Allison Transmission will down drag and downshift like a stick shift all by itself.

[BlackSilver]

Why would you WANT to shift out of 5th gear? The Allison is not your grandpa's DynaFlow, and in Tow/Haul mode it is designed to take care of itself when pulling serious loads.

 

I pull a lot more weight than you're talking about, including a lot of mountain grades, and the Allison is always in precisely the right gear, up hill or down. It's smarter than us --- let it play the way it wants without putting a muzzle on it.

[KyleBst264]

I see you have an '05. I assume there is barely any miles on it right now. The TCM for your Allison Transmission will adapt to your driving paterns over a course of time.

[dannyukonxl]

hmmm does this hold tow haul hold down for a few seconds work on a 4l85e or just the allison

[KyleBst264]

Holding the tow/haul button down to disengage/engage O/D only works for the Allison on '03 and newer. This is because the there is still PRND321 on the selector and going from D to 3, you'd skip 4'th.

 

For the other automatic transmissions, I believe you just put the shifter in "3" to disengage overdrive.