When our '02 D/A,3500,4x4 was newer, a trip to Lake Tahoe and back revealed the grade braking feature worked GREAT. Little by little, it seemed not to work well. We never went back up to 6-8,000 feet, just up to 3,000 ft at most and back down on curvy roads. I took it to my selling dealer who does not have an Allison trained tech on site. They scanned for codes and found none. As of today it works intermittently, about 1 time in 10.

I have asked around and some possibilities are:

a) The Allison lost it's adaptive learning feature because I am a laid-back driver who does not jam the pedal to the metal and because I have not been up to the real, 6,000 ft mountains for a while. I might need a Tech II re-flash (or something like that)

b) The accelerator pedal is not 100% up off the floor when I am decending a hill and is sending the TCM that message and not enabling the Allison to grade brake.

c) There is some glazing inside the Allison (clutch plates?) which prevents the grade braking feature.

There might be one more possibility, but I forget.

I have tried short stab braking and long, slow pressure on the pedal. Even tried no braking going downhill (think grade braking will kick in in 7 seconds if there is no accelerator applied).

Do you have any insight for me, please? Do you know of a good Allison Tech in the Petaluma-Santa Rosa area?

I am going to visit another dealer who MIGHT have an Allison Tech, but I would like to have some solid background info with me, if I do visit this dealership.

Thanks

I will say that I dont believe the allison has gotten lazy becasue you drive like easy. It dosnt learn how you drive.....it learns that at this throttle position in this gear at this ect..... I need to shift this quickly to keep from sliping and not bang. I ran durring the winter being carefull not to go to WOT since I set my programing down for the winter and when i carnked it up wot was still crisp yet the other throttle positions required a bit of learning. Just my expereince. You coula also set it back to fast learn but regardless the grade braking feture donsnt have any learning to it or I dont believe so anyway.....its downshift will have some learned stuff to it but when its told to downshift is all preset and wont change or I dont believe anyway.

Also checking for the throttle apply is very easy if you or any one has access to a scanner. Even the juice/attitude and other programers show this.

The first thing I would do is run a scan with Tech2 or any scanner that can read TCC ( torque converter clutch) apply % and then read rpm slip after the converter clutch is applyed. After the converter clutch is applyed while watching scanner. I would give it part throttle and see if the rpm slippage increases. We don't like to see slippage go over 60 rpm. A triple disc converter shows 0-10 rpm slippage.

mike

Not to jump in on Mike, but are you saying that there is no engine retarding on a descent? If there is, then there are several conditions that must be met in order for the downshifting part of the grade braking to work. Maybe someone else knows them off the top of their head - I will try to look them up, but am leaving early tomorrow to a meeting, so no promise.

Look at TSB #02-07-30-004B. Seldom works with truck alone. Tow haul must be set, throttle up, brakes and brake lights on, and gaining speed, then watch RPM go to 4400+. Trailer brakes will likely be stronger than the grade brake feature unless you turn the trailer brake controller way down. Works good with two stage brake controller - keep soft response set very low, and hard response set high, so you can panic stop it all.
Turnpike

PS: Got to stay on the brakes just enough to keep brake lites on, then it'll really work. With a 11,000 lbs trailer on 7% grade it tends to slow more so than just hold the speed. Just an extra thought. Turnpike.