C-6...1st and reverse work fine. Goes into 2nd and locks up the driveshaft. I disassembled and cannot see anything out of the ordinary.

This C-6 was behind the 460 in the T-Bird in my avatar.

(Edit: This trans was built in 2006 and up till this happened I had 120 trouble free passes )

On my 4th pass at the track last October, I launch with the shifter in "D" and everthing is fine until the trans goes into 2nd.
When it went into 2nd the driveshaft locked up.
1st gear and reverse work fine, but if I manually put it into 2nd or let the automatic function shift it, as soon as it goes into 2nd, the output shaft locks up.
It almost acts like a transbrake from a standstill if I manually put it into 2nd.

So, last night I tore into that C-6. I was relieved to not see a single piece of metal in the pan. Everything looks normal and in great condition.

Question:
Is it possible that 1st is not releasing when second engages ? And if so, would that lock up 2nd gear?
I can drive around in manual 1st as normal as well as go into reverse as normal.

I kind-of suspect now a clog in the valve body or passage.

My 1983 factory service manuals do not explain the functions of the C-6 and what is used for each gear...only how to rebuild it.
Is the intermediate band used for second ?

Any ideas helpful.

If all the clutches and the band looks good ,then you have VB problems
Frank

Yes the intermediate band is only used in 2nd

bad sprag

Thats what im thinking to valve body or vb gasket is leaking trans fuild into the wroung channel.. hope this helps

Thanks guys for the tips.

I did not see anything unusual with the internals.
Haven't disassembled the vb yet, so hopefully all it was was some debris clogging up.