The transmission is not shifting. It starts up in 1st and reverse OK but will not shift into 2,3 and 4th. What could be wrong?

I have changed the followings:

1) Transmission filter and fluid
2) the solenoid inside the transmission from a junk yard.

What else can be wrong, Vacuum, modulating valve? I do not know transmission well and do not find any info in my Haynes manual. Your advise is appreciated.

 

Topic discussed many times on the forum, use Search to view old discussions. Your trouble is likelyrelated to vacuum - checklines to modulator and check modulator itself for proper operation. If the modulatorhas not been changed in 100K miles, or if you've never changed it go ahead and put in a new one.