Harsh downshift

[mattb5150]

Yesterday creeping along in bumper to bumper traffic on the freeway the Allison did a hard downshift, had my Realtor in truck with me and he thought we had been rear-ended, car behind was way back. Truck has 125k on odo and recent(within last 10k miles) internal filter change and switched to Valvoline syn fluid. Any thoughts?

Matt

[dually2002]

Chack the fluid level when hot. Did you change the spin on filter?

[DmaxMaverick]

The most common cause for the "rear ended" feeling during stop/go driving is spring wrap. It can be remedied, at least temporarily, by lubing the tranny output yoke spline. If you are experiencing hard downshifts at or near walking speed or accelerating after stopping or nearly stopping, 2-foot driving is the usual suspect (left foot on the brake). This is remedied by ensuring you have no APP input (right foot on the throttle) during slowing/stopping. The TCM needs to see zero throttle input during the stop, or this can happen. Eliminate the simple (cheap/free) stuff before suspecting something is broken.

[mattb5150]

This instance wasn't like the un-lubed spline feeling it was very hard. Spin on was also changed, need to check fluid.

Matt