Ok so I have a 1966 mustang straight 6 and im not sure on what tranny it has yet. I have only had it for a week or so. I finaly got it running after some problems with getting her started but now I am having an issue with getting her to stay in gear. I put it in D and sometimes it goes in but others it just seems to be in neutral, same with R. Sometimes while Im driving and then stop at a stop sign when i let go of the brakes and tap the gas again it will have sliped off gear. Can this be the "modular valve" or vacuum valve? Not sure what its called, but it mounts to the tranny with a hose connected to my intake.
Please help, I have the valve off now but am debating on buying a new one.
Also while I was trying to get the valve off I think that the hose might have had a little crack on it from dry rot. Im not really sure if I did that or if it was there.
Thanks
David

 

A cracked hose going to your vacuum modulator can cause those symptoms.

 

Changed out the modulator and the hose, added some more tranny fluid and she is shifting fine now. I think I am going to drain all the tranny fluid and change the filter and put new fluid in cause it looked dirty and was smelling burnt.
Thanks for the reply