RV Repair: 1981 chevy 400 transmission in 81 coachman, th400 transmission, servo valve

Question
Hi Bill,
 I have '81 coachman on Chevy van frame.  Transmission only shifts 1st and 2nd gear.  When shifts into 3rd gear transmission binds and lugs engine down. sort of like it is shifting into reverse or something.  Moving shift lever into 2nd gear clears this condition as transmission shifts back into 2nd gear.  I have a used chevy TH400 transmission that I can swap out for this one.  However 2nd transmission has "long tail" and Motorhome has "short tail"  what do I have to do to swap the tail sections of the transmission?


Thanks in advance for your help.

Richard

Answer
Hi Richard:
Sounds like trouble. My guess is your trouble is with second gear not releasing when it shifts into third binding things up. For some reason the second gear servo valve does not release. What I would try first is an additive to break loose any varnish that may have built up. Most parts houses carry some stuff called "Trans X". If varnish is the problem that stuff will clean it out, follow directions on the can. If all the rest of your other transmission is the same then probably the best way to do it is to have a machine shop extend the drive shaft to make up for the shorter tail shaft. In order to change the tailshaft you would also need to change the transmission output shaft which is a problem. Good luck!
Bill