Allison 5sp: Bang in reverse

[05chevy]

Just did a PPE stage 4 for a friend. When everything gets to operating temp you hear a loud bang in reverse. What could be the cause of this?

 

[RENODMAX]

Is it only when the fluid is warm? One transmission I have seen and had to trouble shoot had too large of a clearance for the C3 and the apply piston was moving too far and had a tear. Cold it would work fine, warm it would bang and eventually lose reverse all together.

 

[05chevy]

Is it only when the fluid is warm? One transmission I have seen and had to trouble shoot had too large of a clearance for the C3 and the apply piston was moving too far and had a tear. Cold it would work fine, warm it would bang and eventually lose reverse all together.

Yes only does it when the fluids are warm.