Trans Pros, Pleas help- Turbo 400 problems

[howdies86]

Guys, let me start off by saying that I have owned several GN's and a stg. 2, 8 second T-Type, and have most always done my own building, both trans. and engines. Now I have one that I can't diagnose. It is a Coan turbo 400, 8" converter, reverse valve body w/brake that my son bought new several years ago b/4 be deployed with the Army. Long story short, the trans acted like it would shift to 2nd gear and go directly to 3rd w/o moving the shifter. This was on jack stands. Coan thought it was a broken rear sprag, so I tore it apart, inspected everything, 34 element sprag looked ok, so to be safe, changed it anyway. Started car, still couldn't tell any difference. Drove it,1st gear, ok, shift to 2nd, seemed ok, third, no shift!!! Ran it up and down several times at 4000RPM still no shift. Linkage is correct. My son, who is Stateside now, and I are are totally confused. The transmission never had burnt fluid issues and only had a few "street miles" on it b/4 he was deployed. "Transmission Builders", please chime in!! We are tired of laying underneath the car and spending money. Coan says, send it back, they will inspect it and advise. My son, who is a 17 year veteran, does noy have the money for this and I have basically Come out of semi-retirement to help him. Any ideas?? Thanks. Howard and Clint

 

[jakeshoe]

First,
The obvious, check fluid level and then shifter adjustment. Check it with the shifter unhooked in the 3rd position.

Next,
Drop the pan, be sure the rooster comb is tight on the manual shaft.
If all looks OK, measure the position of the manual valve in the VB with a pair of calipers.

Drop the VB and put the manual valve in the exact same position and see if it is open to the 3rd circuit.

Air check the 3rd clutches while you are there...

Are you sure the sealing rings were installed properly on the center support?

A RMVB is pretty dumbed down, so no third is either an adjustment issue, the manual valve not getting far enough back (adjustment, tolerance stack up, etc) or a 3rd gear clutch issue.