trans wont change

hi everyone. i was driving my 71 302 maverick with c4 aotu trans today to the store and it was changing normal. after stopping at a red light, when i took off car wouldnt change from first gear. pulled over and oil level is good. reverse goes in and park as well but wont go past first gear. any ideas of what might be problem or how to fix? thanks

 

First things I would check would be the linkage and the modulator. I'd do the linkage first just cause it's the easiest to see if anything is wrong. if it goes into reverse and park. I'd think linkage is not the problem, but I'd check it anyway then I'd try replacing the modulator. After that I'd be waiting for Paul to show up on this post.

 

I would check the Modulator and or vacuum line going to the modulator.
Jerry

 

Check your vacuum line. They always come off.

 

Well, they may not always come off but the modulator is what determines the shift points at anything but full throttle. I would check the vacuum lines at the modulator and the other end at the manifold or distribution block on the firewall.

 

i changed the modulator today and car now changes from 1st to third but after a get to 30mph. it skips 2nd.

 

Did you try adjusting the new modulator? There is a procedure in the manual on how to set it.

RS

 

It may be shifting so early you dont feel the 1-2 shift or so late that it is not in third yet. The modulator rod has to be in the modulator and the hole in the back of the valve. Try getting on it hard from a start and see if it shift 1-2-3. If not then you may have the rod out of position.
DO NOT adjust the modulator - the adjustment is only for fine tuning not big adjustments. If you want firmer and later shifts replace the rod with one that is not over the max length. For push-in modulators that is 1 5/8" and for screw-in modulators and C5s it is 1 3/4".