Stupid Question About The Allison

yukon25008.1 · November 4, 2011

I have a question about the allison in my 05 sierra 8.1 4:10,s

if im going down a hill and get out of the throttle the truck seems to downshift 1 or 2 gears and rev 500-1000 rpm,s higher..Almost seems like a jake break feature.

Then if im down the same hill and put the truck in nuetral and it revs 500-1200 rpm,s higher..?

in neutral shouldnt the rpms drop down to idle speed??

Thanks for the help

Shaners · November 5, 2011

My Dmax likes to downshift coasting down hills especially if I touch the brakes. Even more so if its in the tow/haul mode.

alaska511 · November 5, 2011

It is the grade braking feature in the Allison. Are you in cruise, or T/H?

yukon25008.1 · November 5, 2011

Just in drive.. no cruise no tow/haul

Also thats when i notice it starts as soon as the brakes are touched..

Patch6713 · November 5, 2011

I read that the Allison uses grade braking while in Tow/Haul mode. However, since the Allison is a five speed, and the gear selector only allows for drive, 3rd, 2nd, and 1st that it uses grade braking from drive (5) to 4th at all times and that it activates something like when you apply the brakes or the truck feels that you are picking up speed down a hill. I don't have an Allison, but read this I believe on a diesel forum a few weeks back.

Shawn T · November 9, 2011

_{His truck is an 05. It has an overdrive cancellation button starting on 03 models. Essitially holding down the tow/haul mode button for 2 seconds creates the ability to downshift into 4th gear. Grade braking is always active on the 5 speed allison tranny. It just exagerates it in tow/haul mode. Also the 5 speed has cruise braking. My 03 behaved like this and I really liked these 2 other features. My 06 has to be in "D" and tow/haul to grade break. If you put it in "M" mode you have to grade brake "manually" using the up and down selector on the column. Truly I wish they would have not added that feature and left the tranny as it was but added the extra overdrive and just let you select the gears using the column shifter. My 06 will take off down Vail and Eisenhower passes, when before with my 03 it would hold my speed with gearing in cruise or not}_.

yukon25008.1 · November 10, 2011

So if i hold the tow/haul button in I can be in 4th vs 5th or 3rd?

Shawn T · November 10, 2011

Yup, it should have 2 icons on the gear selector lever. a small arrow showing the "trailer" for tow/haul mode, and a long arrow (suggesting you hold it down) pointing to an overdrive symbol with a ghostbuster slash through it. That will hold you in fourth gear and a light will illuminate on the instrument panel. Sounds kind of elementary but thats my best shot at it

yukon25008.1 · November 12, 2011

I tried.and it didnt do anything.. in D i held the tow/haul button for 2 seconds and nothing happened..

Its an 05

Shawn T · November 14, 2011

Does the selector have the icons I explained (It was an aweful explanation, I know). It should have a long arrow pointing to and overdrive symbol with a slash through it (just below the short arrown pointing to the tow/haul icon). The longer arrow signifies to hold in. Hold it down (how many seconds, I don't know) and it will downshift and an orange icon (same as on the gearshift) will appear on the upper left of the instrument panel. I had my brother go out on his 03 this weekend and it worked. I used it tons of times while pulling with that truck. Does the tow haul mode activate? May be a relay or trouble with the TCM. This was a big complaint in 01-02, not having a 4th gear hold down. That was GM's rememedy in 03-05.

yukon25008.1 · November 14, 2011

my tow/haul does work..but i only have one button on the inside of the gear selector/handle

gmtech4 · November 15, 2011

does your owners manual have the proceedure ????

yes it does ,...jeez louise !!!

guys are killin me !!! lol

yukon25008.1 · November 15, 2011

Does the selector have the icons I explained (It was an aweful explanation, I know). It should have a long arrow pointing to and overdrive symbol with a slash through it (just below the short arrown pointing to the tow/haul icon). The longer arrow signifies to hold in. Hold it down (how many seconds, I don't know) and it will downshift and an orange icon (same as on the gearshift) will appear on the upper left of the instrument panel. I had my brother go out on his 03 this weekend and it worked. I used it tons of times while pulling with that truck. Does the tow haul mode activate? May be a relay or trouble with the TCM. This was a big complaint in 01-02, not having a 4th gear hold down. That was GM's rememedy in 03-05.

I checked it out..and the shifter does show what your talking about, but when i held it in nothing happened

Shawn T · November 15, 2011

There is a bigger problem then. Run through the procedure in your manual. Like I said, I used that function dozens of times in my 03, never a problem, worked every time. I would post your issue in the tech forum, surely they have ran accross this issure before. Good luck. Yeah, his owners manual does have the procedure, but if he didn't know the function existed in the first place how was he to know to even look for it?