Allison vibration in T/H

[HisDMAX]

I recently noticed a vibration in T/H mode when shifting between 2nd and 3rd. It happens just as it is about to shift about 20 mph and 2000-2200 RPM. The best way to describe it is that it sounds like I am running over rough pavement. It is not all that loud but is definitley noticable. It feels a little like it is hanging up a bit before shifting. I first noticed it when towing a small trailer 1500 LBS. The truck only had about 3500 miles on it at the time. I checked and it also did it with nothing in tow. I recently traveled about 1000 mi with the trailer and supplies. Mostly highway. It is not as frequent now but it is still there it is happening at higher RPM but I figure that is just the trans adjusting after towing more. I don't know if this is something to be concerned about or not any feedback would be appreciated.


Mike

[dmaxalliTech]

Mike, its possible that the adapts are skewed alittle. Is it noticable in regular mode? In t/s the t/c is locked up sooner in lower gears and is unlocked during a shift then locked after the shift is made, could be a conveter shudder but would think it noticable in other gears too. Unless your getting it at a certain rpm which is common with your 2-3 shift. Is it more consistant with rpm or shift? Regardless, I would take it in and have it looked at, if nothing else to get it documented

[a64pilot]

If it's doing it at full throttle and is about the same frequency and ampllitude as wheel hop I'll bet it's Tq converter shudder. In my truck it's so violent there's no doubt that your doing something bad.