engine grade braking won't engage???

[biker Wayne]

I've seen a lot of posts of people saying their allison will automatically downshift going down hill and a lot of people saying theirs won't downshift. I've tried on 2 different hills, 1 a 6% grade. I'm pulling a 10,000# trailer with a 1300# motorcycle in the bed. From 35 mph it went all the way to 55 in 4th gear and never shifted down to 3rd even though I braked twice going down the hill. Tonight I tried turning the trailer brakes completely off and braking on a short hill. From 40 mph it would gain 8 to 10 mph to the bottom of the hill and not shift down to 3rd. At 40 mph it was at about 1700 rpm, so it should have had enough rpm room to shift to 3rd.
Has anyone found out the conditions needed for engine grade braking to work(load, how long and how hard to brake, how steep of a hill, how long of a hill)? From what I've described, should mine have shifted down? Has anyone had their transmission fixed so that grade braking would work?
Thanks.

[MudNurI]

I can pretty much make mine engage...now what exactly I'm doing I don't know. I can do it just about anywhere, on any hill etc. I've never towed anything, so this is all empty

now are you in tow/haul mode???

have you tried without anything behind? no trailer just driving normal?

Just a thought, how's your power, are you upshifting okay? When mine was in Limp Mode, I lost my engine braking TOTALLY, didn't matter what I did, it wasn't going to do it.

sorry for all the questions, but I really don't know what I'm doing to make it engage..

Brandy

[bora]

In normal mode, the engine braking will engage
when you press and hold the brake pedal for about 5-10 seconds in mine.

In tow/haul mode, almost instantenous downshift and engine braking when I press the pedal for a few seconds.

[mattb5150]

Mine has grade braked unloaded on the highway. But I was wondering if anyone knows if maybe the grade braking is switched off when you are in four wheel drive. I took a group of people out to look at a logging job and the truck didn't want to grade brake coming back down the mountain in regular or tow/haul. I was in four wheel the whole time and had to ride the brakes or free wheel.

Matt B.

[biker Wayne]

MudNurI,
Yes, I'm in tow/haul mode. The upshifts and downshifts while slowing down work fine. The power is fine (an add-on chip would be nice). It won't grade brake with no load.
I'm wondering if the people that have grade braking also have the shift busyness and vice versa. Mine will hold 60 mph in 5th on level ground. On hills it will drop 4 to 5 mph or 60 mph, whichever comes first, before down shifting.
I also wonder if the 01s tend to grade brake more readily than the later 02s (mine is an 02). Mine has all of the latest ECMs; do the ones that will grade brake have the latest ECMs?

[TLA]

Remember, you can always pull it into 3 on the shift lever. The tach can go into the cross hatch red. When you touch the throttle, the computer will not let it over rev, shifting up into 4. I've had to do it this way several times.

[Jackmchome]

I copied this off the web a long time ago. Seems to answer the question. Good luck.

The Allison Grade Brake Feature is a wonderful feature if you understand how it works and what inputs the computer needs to activate the downshift.

1. The Grade Brake Feature is intended to anticipate the need for a downshift so that the driver will not have to shift the transmission manually


2. The Grade Brake Feature is more aggressive in Tow/Haul Mode. By more aggressive I mean that the Allison will down shift without a brake apply if the computer reads a 0 from the foot feed, or TPS in tech speak, for 7 seconds while the vehicle speed is increasing or remaining constant, not losing speed. If further downshifts are needed the driver must tap the brakes, approximately for 1 to 2 seconds, to get more downshifts.


3. The Grade Brake Feature is not as aggressive when Tow/Haul is not engaged. This means that the Allison will only downshift to 4th gear when the computer reads 0 on the foot feed (TPS) and the vehicle speed is increasing, i.e. down a steep grade, or when the brake is applied for a 3 to 5 second duration.


Personal opinion and after some doubts I have come to depend on these downshifts, to the point that I drive in Tow/Haul all the time with or without a trailer or heavy load. Tow/Haul has other benefits like holding lower gears longer which in heavy stop and go traffic has helped keep a reasonable distance between me and the vehicle in front of me. The Grade Brake Feature is helpful when exiting the freeway, the Alison downshifts to slow the vehicle with very little input from me. I must admit that when I first tested the Alison and the Grade Brake I was skeptical, until I used it the way it was intended. Now when I climb back in my Buick, yes I do have a car, I miss the Alison and the Grade Brake. Just another reason to have the truck I guess.