Just bought a 1977 and the transmission will not shift into 3rd gear. When it was cold the s'morning it shifted fine through all gears, went about 5 miles and it shifted back into 2nd on it's own. The guy I bought it from said it was rebuilt a year ago with no issues. Any suggestions?

 

Check the hoses that join the modulator valve to the intake manifold. The short hose that plugs onto the modulator valve gets soft from oil saturation then either splits or comes off the modulator valve.

 

Thank you, Will check that out.

 

Checked that out and it was fine... Any chance it could be the detent cable?