It's got me and my Transmission guy stumped. All the usual bits strengthen including the addition of a "Z-Pack". Powered by a stroked and cammed LS1 with a Yank PY3400E torque converter. Under acceleration all changes are nice and crisp. Really happy with it. Under light acceleration, all changes are clean and crisp with the exception of the change from 2nd to 3rd. Increased the line pressure, reduced the line pressure, pulled the box out and checked the Z-Pack, all to no avail. My transmission guy has put in literally a hundred + Z-Packs and hasn't had a problem. Both of us are stumped and so I thought I'd share the problem in the hope someone has had a similar problem and has solved it.

 

"Clunk", as in harsh shift? Does it flair before the clunk? Does it ever slip? What 2nd servo is in it? What 2-4 band? This may be a shift timing issue. I'd have to know more about what other mods have been made.

Frank
CPT

 

A better description of the 2-3 shift clunk would help here? At what throttle opening is this happening? Part throttle? Full throttle? Does it make a clunk on the 3-2 downshift when coming to a stop?