Allison 5sp: Harsh 2-1 Downshift

[lts1ow]

Its not all the time, and I can't seem to recreate it consistently.

But coming to a stop, if I stop quickly, seems to hang in 2nd, then when stopped clunk into 1st. A harsh clunk at that. BUT, if I slowly stop, I can watch on the CTS it go 2-1 with no issue.

Thoughts?

 

[Mike L.]

Try a different tune.

 

[lts1ow]

Try a different tune.

Will do, also was going to do a trans relearn.

Come Monday I am swapping fluid and spin on filter since they are due as well.

 

[Mike L.]

Will do, also was going to do a trans relearn.

Come Monday I am swapping fluid and spin on filter since they are due as well.

Don't do that.

 

[lts1ow]

Don't do that.

Fluid swap, or trans relearn?

 

[Chevy1925]

Fluid swap, or trans relearn?

trans relearn.

 

[THEFERMANATOR]

What tcm os are you running? 01 or 05? Some of the 01 os's have a harsh 2-1 downshift(there's a tsb about it).

 

[lts1ow]

What tcm os are you running? 01 or 05? Some of the 01 os's have a harsh 2-1 downshift(there's a tsb about it).

Its a canned PPE tune, and it is a sudden issue. Truck has been tuned like this for a few years now.

 

[snowman22]

My old LB7 started doing strange things when cold on the 2-1. Couldn't ever figure it out, and it wasn't the driveshaft, I already lubed it.

Flash forward 6+ months and after servicing the brake system, gone. I replaced all four corners with new pads, rotors, and flushed the fluid. I could be a coincidence, but I would bet not.