Chevy 8.1L/Allison combo

[Mike_E_]

Hi there,

Does anyone know if when an '02 Silverado with the 8.lL/Allison set up is in Tow/haul mode if there is any sort of 'engine braking?'
Seems to me that a tap of the brake pedal when on a downgrade might cause it to downshift?

I could be completely delerious, so if there's anybody out there that can either confirm or deny this it'd be greatly appreciated.

Cheers.

[mkirsch]

That's my exact truck and I've figured out that it takes 3 seconds of braking at a steady speed to activate the "grade braking" feature of the Allison transmission, with the tow/haul mode activated.

There's one grade down into town that I use it on running empty, and it holds the truck at 30MPH, the speed limit, all the way down without me touching a pedal.

[hornet28]

I wasn't going that fast when I saw the 4500 rpm but it sure was a long steep grade

[larry_barnhart]

I feel why let the rpm's get to 4500 or even 4000. To me going slower at the top of the incline is the answer. Only because I feel this way the engineer's have figured the trannie will not hurt the engine. I have had to hit the brakes a couple of times to downshift on our 2001 8.1 or even on the 05 duramax. Nice feature that all can do because of the Allison.

chevman

[wnjj]

hornet28 wrote:
An increase in speed is what causes the downshift not an increase in rpm

You’re right. My brain said RPM since that’s what I associate with the engine noise as a truck speeds up downhill. With the torque converter locked they’re one in the same anyway.

[hornet28]

An increase in speed is what causes the downshift not an increase in rpm

[wnjj]

hornet28 wrote:
Actually taping the brake doesn't cause it to immediately downshift. What it does is keep the truck at the speed you were traveling at the time you hit the brakes by downshifting when needed and not just one time. I saw rpms as high as 4500 coming down some mountain roads with my 02 8.1/Ally

You’re both right. If I tap the brakes when the RPM’s are low, it will nearly immediately downshift. It knows and/or quickly senses the increase in RPM when you lift back off the pedal. Also if you just hold the pedal without decreasing speed, it downshifts to help out. It’s possbile different years have different programming too.

[hornet28]

Actually taping the brake doesn't cause it to immediately downshift. What it does is keep the truck at the speed you were traveling at the time you hit the brakes by downshifting when needed and not just one time. I saw rpms as high as 4500 coming down some mountain roads with my 02 8.1/Ally

[Mike_E_]

Thanks everyone.
Don't have the truck yet, so just wanted to clarify if that feature was there.
Having a hard think about grabbing one.

[austingta]

Absolutely it downshifts. It's certainly different than a 1500. It makes you think you'
re driving a real truck!

[KD4UPL]

Yes, in T/H mode it will down shift for you when you step on the brakes.
Do you have a manual for the truck? It should describe the feature in detail. I use T/H a lot even when not towing just for this feature, it saves on brake pads. My factory rear pads last 185,000 miles, the front pads a bit longer.

[FishOnOne]

This is what the Allison transmission was designed to do when in Tow/Haul

[ugeesta]

Yes it does and happens to me when tapping the brakes while going downhill too.