I tried installing the torque convertor (9.5 inch Dynamic) in my trans today (727) and spent most of an hour trying to get it to seat.
I've had one that took a few minutes to install but I've never had it be a problem like this before.

It engages the pump tabs but won't seat any farther in.
I've pulled it out and tried again 4 times.


Any suggestions on what the problem could be?

Pump tabs are the final destination, have you checked for correct spline count?

I haven't checked the spline count yet.
I'll check that in the morning.

It should have 3 steps in as it seats, correct?
(what I remember)

It seems to step in one time, no amount of spinning/twisting it seems to get it to seat the next level.

I assumed it was the pump tabs as when I pulled it back out they looked lined up with the convertor.

We spent all afternoon once three of us taking turns and nothing! Drove into town to the speed shop i got it from he said that's the way it is some days! Other days it's clunk, clunk clunk!! went back buddy walk over and put his hand on the converter and clunk clunk all the way back.
I pull it back 1/8" and try spinning both directions a little helps too. if it's too far back the converter snout keeps turning the pump tangs as you turn the converter!

Some line the pump taps horizontal with a screwbar then line up converter notches and try sliding it in that way!

You will get it make sure it's all the way back!

I finally got it to seat.

I've spent hours trying to spin it in sitting on the floor with no luck.
I had to hang the trans by the bellhousing from the engine hoist.

I spun the convertor for about 30 seconds and it finally dropped in.

Pics of what it took to get it to seat.





I hope I never have anther one be this much of a pain.

Yup, it's much easier if the trans is vertical. Looks like you've marked the offset lug as I do, along with the matching location on the flex plate.