Allison Tranny Harsh Shifting

[chipper]

I just returned from a 2500 mile trip in the B.C. Canada hills pulling a 12,500 lb 5th wheel. When pulling big grades(6-8%), & the tranny shifts from 3rd to 4th with full throttle, the shift is so hard it pops your neck. All the other gears shift smooth. Any one else noticed this,& do I have a problem? :confused:

[hoot]

Cheaper than going to a chiropractor!

[hammer]

Chipper,My 3500 shifted rough untill I got some miles on it.I beleive it was because the tranny was new & wasnt broke in yet.Im pulling 26,800 Gross load.Ive got 27,000 miles on it now & it dosnt seem to be as aggresive as it was when I first started pulling.Of course yours could be something else going on.Everybody's truck is different.Good luck & hope it isnt anything serious.Hammer smile.gif smile.gif

[hoot]

When the transmission/TCM calibration is new, the TCM is in fast adaptive mode. In other words, the TCM is allowed to make relatively large changes in the adaptive values after each shift. Once the TCM determines that a given shift is close to its ideal level, it switches to slow adaptive mode. In slow adaptive, the TCM still is evaluating shifts and changing adaptive values, but is only allowed to do so in smaller increments. When a shift switches from fast to slow adaptive mode, it is described as "converged". The TCM is programmed to try to switch from fast to slow adaptive mode in as many as 15 to 20 shifts. It is important to understand that there are many different distinct shifts recognized by the TCM, and each of these shift have its own adaptive values. For example, there are upshift and downshifts to and from each range, as well as unique adaptive values for several different throttle regions for each upshift and downshift. The point is, it may take a significant amount of time before most of the shifts converge from fast to slow adaptive, and thus it is not unusual to experience somewhat harsh or unpleasant shift quality until these shifts are adapted.

[Billy14]

I think Hoot is right on the money. When I first installed the Juice, I did the tranny fast learn routine & drove the H e double ll out of it. I noticed when starting off realllllly slow & easy the shifts from 1st to 2nd & 3rd were super hard & jolting. After about 2 weeks & 1500 miles shifting smoothed out again.

Billy

[chipper]

Thanks for the help guys. I guess the important message is that I don't have a major problem.
It sure was a brutal shift though & it happened several times. :D :D

[ardmore]

I have the same problem, on an intermittent basis, every 15 shifts or so when pulling my 5th wheel (11,500 lbs) when it is upshifting from 1st to 2nd. A very jolting shift. Dealer refuses to change the TCM, says he cannot get approval of GM engineers for new part (warranty purposes). My 2002, 2500 Duramax has 9k plus miles on it most of this has been towing. I think I'll elevate the problem to the Regional Service Manager. The TCM should have "learned" my driving habits, etc. before 9k miles, and made appropriate corrections in shift patterns.