Tiptoptune
11-13-2003, 22:02
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.
Thanks in advance for any help.