Trans Grade Braking not working correct

[Tiptoptune]

Our Trans brake stopped working the same as did when new. Have 03 Silverado LT Crew 4x4 longbox dually Dmax allison. Tow 14,000# 36 foot rv, 2001 model with electric brakes in good shape and properly adjusted. Scaled and we are darn close to the max 22,000 GCVW. Brake worked what I feel is normal for first 2500 miles of towing and 17000 total miles on mostly major highways anywhere from Indiana, Wisconsin, Colorado and all between on both flat and 5% grade. Then going down 7% grade for 11 miles ( Wolf Creek Pass on Hwy 160 CO ) I was doing 40 most the way, slower on the tight switch backs, using the truck brakes on and off, did not add any more trailer brakes than what I had our Tekonsha Prodigy set at ( 10 out of 13 and 6.3 boost )all felt safe, but 2/3 rds the way down started smelling brakes, hoping they were trucks in front of us but they were ours and when at bottom we had to stop for construction, our trucks rear brakes started smoking after stopped for about 1 minute. No fire, had extinguisher ready, and then got moving in another 2 minutes and all seems fine even visual inspection only damage looks to be coating on brake disc shield discolored and peeled. Why I tell you all above is the trans brake did not seem to engage as much as I feel it should have and this seemed to be the beginning of the degrade in trans brake operation. Then traveling to Grand Canyon and North through Utah the trans brake definately was not coming on when descending steep grades at 60 plus or minus and using foot brake quite a bit and even manual trailer brake for needed more braking. I did up the setting on controller to near max after brake smoke incident and experimented turning it down and off to see if trailer brakes influencing trans brake operation and no change in trans brake operation.. Seemed tow haul mode switch was signalling tcm that it was on for when I would switch it off engine rpm would change a houndred or so rpm. I feel there was at least a dozen times if not two dozen times the trans brake should have and would have when new engaged in this stretch of Utah highway around Lake Powell and it did not. The trans brake did engage twice on this paticular stretch and it REALLY ENGAGED during a grade brake downshift 5th to 4th to the fine tune of 4000 plus rpm instantly, it was even near 5000 rpm. I was scrambling to shut it off for fear of engine damage. After this I decided time to take it in. Went to Brent Brown Chevrolet Buick in Provo Utah, they said they had some experience with the D/A, took a diagnostic tech for 30 mile ride with trailer hooked up down some 3-6% grades that were pretty turny at bottom at highway speed and trans brake never engaged, had to be on truck brakes hard at times. Even turned off trailer brakes and did long consistent hard truck braking, both steady on pedal and on and off. I asked them to "flash" or check the tcm for updates from what I learned on this site. They had never did this and took time to call GM tech support and they said they were able to check it and it had all the current updates. Truck was built 10/02. There fix was to give me New Product Information - Grade Brake Feature Of Allison 1000 Series Transmission #02-07-30-004A-(09/11/2002) Corporate Bulletin print off from GM explaining operation of trans grade braking. It states in the bullein that, "Engine rpm immediately following a preselect or grade braking downshift can be as high as 4000 RPM. And after a grade braking downshift, if vehicle speed continues to increase, an upshift will occur at 4,800 rpm". My question is, has anyone ever experienced the above, inconsistant operation and the high rpm spike? Also any suggestions on where to take truck for service? I feel there definately is a problem with the inconsistant brake operation, although the high rpm spike may be normal. We are at Breckenridge Colorado for the winter, about 1 1/2 hours west of Denver Colorado. Sorry about the long post, but wanted to give some history. Truck has never been in for service other than rv mirrors stopped extending the first time we really needed them - see my other post, rv mirrors do not extend long enough.

Thanks in advance for any help.

[Viking]

Tiptoptune,do you recall what the transmission temperature was indicating when you were going down the long grade with the tow haul engaged? Fluid level and condition? I get the "spike" as you say when the downshift occurs but mine has never failed to engage with my 10,000# trailer. You will have to find a dealer that fully understands the transmission.

[peachin]

To Review - you were in the T/H mode for this braking. Sometimes two touches of the brake require the downshift kick in - as it will continue to downshift at various lower speeds
from 5th to 4th to 3rd to 2nd to 1st. The engine will not overrev as it has a "kick out feature" at the high 4000 rpm level.

In non T/H mode it only has the braking feature from 5th to 4th.

In T/H after you hit the brakes, a downshift should occur, unless you are going too fast for the next downshift - then you need to hit the brakes hard but not sharp until the sensor sees that your engine is not going to fast for the next downshift.

If you are in a downshift mode - the second you hit the (gas peddle) fuel - the downshift pattern will kick you out of it's mode. you can also get out of the mode by "tapping out" the T/H mode.

All of this would be adjusted by hitting "O/D out"
as you will not reenter a higher gear above 3rd or 4th.

If your system is not working as described above - then you need some Allison work (modules etc) not Chevrolet diesel work - I wonder? Does Allison also warrantee the tranny so that you can go into an Allison shop?

I haul Heavy all the time and have done the entire Northwest and Southwest Mountains - I might consider not having a Duramax - but I'll never go back to anything less than the Allison!

I guess if we were together in the same area - or you could have someone experienced in towing drive it - they could immediately tell - if you got what you were suppose to get!

hope this helps, Peachin

[Tiptoptune]

Viking, as I recall trans temp has been in the 160 to 210 range and all points between when the problem has occured. I have had it work when temp up at 210-220. Fluid is original and on the mark, I have changed the external filter and did not forget magnet thanks to this site.

Peachin, I have experienced the need to tap brake pedal a couple times to get it engaged and on the times it has not worked I was having to get on and off the brakes quite a bit to avoid constant brake pedal and still no engaging. Also to cancel the t/h at times I have had to actullay depress throttle pedal 1/4 to 1/2 way to get it to come out of the grade brake mode. This seems to happen when still descending or even on flats and when I wish to accelarate, not slow down. Just the last two days I have driven truck empty to Denver on I-70 from 11,000 feet to 5,200 feet and the grade brake did engage at times and also had to get on the throttle pretty good to get it out of grade brake mode.

Really seems to me it needs a check up - has other quirks(hazards make bad buzzing noise and shut off after 60 seconds of use, seat memories do not work the way they used to, A/C does not cool real well). Has 21,000 miles on it. Anyone on a good dealer around Denver to take it to. I am about 100 miles west of Denver.

[peachin]

I would take the truck in with your list of everything to a dealer - one that has lots of
diesels on the lot - and show them each item on the list and ask them to call you when they are ready. Then check your list out when it is ready - preferably with a service person - and anything that still is not working - give it back until they get it right. GM use to have regional people who handle problems when repeated service does not solve the problem. Keep pushing them and always add any comments to the service order - so that any unresolved issues after warantee - are still under warantee. Ask for the moon and be determined! Of all the Mfg's GM is the best.
If it were a ford or a chrysler product - you would get lots of run around with products with built in problems. That's a for sure!