Rough road down shifts

[Smitty77]

04 coach with ISL and 3000 transmission. When under load power, say climbing a hill, or when accelerating up to speed on a freeway merge. If I hit rough part of road, say a pot hole I can't avoid, I'll get a quick down shift in gears, then usually it will upshift back to where was again. (I say usually, as sometimes for driving reasons, I'll need to come off the fuel pedal.). This happens most frequently in 6th down to 5th, or 5th down to 4th - but I believe to just be timing of where I am. It does seem to me that it is again while the engine us under load.

No error codes on Silver Leaf or the Allison shifting panel.

I've unplugged, inspected, replugged one of the harnesses back in the engine bay.

I had one person suggest I have my coaches ABS sensors, at the wheels, checked. (Which, I will do.)

But wanted to ask for any other recommendations to have checked out. It's the majority of the time just a nuisance, and has not seemed to increase in frequency. And has been occurring for at least 4-5 years. Finally, it is not an all the time occurrence. This years travels it has happened at least 5-7 times over about 5K of travel.

TIA for any suggestions, and best to all,
Smitty

[Ray,IN]

I've had that happen a few times every year. I have concluded it is timing, a downshift is about to occur when I hit a pothole or quickly go from gas to back off gas pedal or visa versa.



I doubt the ABS sensors are involved, they are not connected to the Allison.
For a Spartan Chassis only:
To calibrate the wheel ABS sensors, build air pressure, turn off engine, disengage parking brake (wheel chock), push hard on brake pedal, turn on key(do not start). you''ll hear a click 4-6 of them. That's the calibration procedure, which also activates the automatic slack adjusters to adjust the brakes.
Can't speak to other chassis.
An aside to the ABS. If you have an intermittent or solid ABS dash light, before spending money, use a pressure washer from the opposite side to spray the back side of the wheels on other side. Sometimes dirt and debris get in the tone-ring slots and trigger an error. The spray job often cleans the offending dirt/debris away.

[dbarton291]

The Allison TCM knows when the ABS is active if the vehicle is wired correctly. When ABS goes active, the transmission will disengage the lockup clutch. That may or may not be what you are feeling.