Push the yoke all the way into the tranny then back it out 3/4". Now measure from the center of the U-joint (on the yoke) to the centerline of the where the U-joint goes on the pinion. I used a magnet to hold the tape measure on the yoke & pulled the tape measure towards the tranny. It's easier if you have a friend help you measure it though.
Driveline Northwest told me you should have 3/4" to 1" play. Any tighter and you'll take a chance of breaking a tranny. Happened to me on a TH350 once
And to loose, well....you get the picture
Follow Genes advice though and ask them to spin it at a higher rpm when they balance it. Shouldn't cost any more, some refer to this as "Performance Balancing"
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Lowered '67 Elcamino
ZZ430 eng / 4L60 trans
"Canyon Carver"
[This message has been edited by Cardiac (edited 01-06-2000).]