6 spd allison shifting terrible and locks up in 1st

[Duramaxordie]

Alright guys I have a truck here in the shop that has the 6 spd Allison that is from one of our car lots. It sill go through all of the gears but it shifts horrible and when slowing down to a stop when it shifts down into 1st gear the whole trans locks up dragging the rear tires then if you let it sit a second it unlocks. Also if your in drive and keep it in first like pulling it in and out of the shop it it will go in and out of gear. I have searched around on the internet but havnt found anything that explains my symptoms, I'm trying to figure out if it is in the VB or if it is internal and i need to go ahead and pull it and take it to be rebuilt.

 

[IOWA LLY]

Does it throw any codes? Could be a bad TCM....

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[Chevy1925]

you should know what step number one is, specially on a job vehicle.

 

[Duramaxordie]

Sorry i guess i left out some useful info. It have no TCM codes, already dropped the pan and it is shiny clean no clutch material and fluid is pretty well clean and full. Also checked front and rear diff fluids and transcase fluid its all go nothing out of the ordinary.

 

[Duramaxordie]

Also when it shifts hard its not like slamming gears as much as when it shifts it feels like you hit something with the truck slowing you down.

 

[IOWA LLY]

And here we go again......

Where did I put my dam crystal ball at now.....

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[Mike L.]

Sounds like the internal filter is restricted.

 

[J_Stone06]

Could it be trim valve/solenoid* related in VB? I read somewhere before when someone had super hard shifts IIRC.