Good morning everyone and Happy Father's Day to all you dads out there.

I've got an issue. My car isn't shifting out of low gear. I was going to take it to work today, and everything was good until I turned to leave out of the neighborhood, so I limped it back home. It was fine Thursday when I drove it, so this is all of a sudden. I obviously haven't had a chance to troubleshoot, but
I dunno where to start. Any ideas?

It's a '72 Supreme with a TH400

 

Make sure you check the transmission fluid level. Hopefully it's something simple.

 

Dave - My bet is the governor, but the first place/thing to evaluate is the automatic transmission vacuum modulator valve:

(1) Check the vacuum hose from the intake manifold is not ruptured, broken, disconnected and the metal line has not disconnected from the rubber hose.
(2) Examine the area of the transmission where the modulator valve is installed into the transmission for excessive ATF fluid, pull the valve and evaluate.

If all appears well, I'd check the kick down solenoid - maybe no voltage/current to the solenoid? Don't know TH400 very well, I play w/ the TH350.
Next, check the governor.

 

Th400 tranny not shifting

 

That was my first thought, but as I said above, no issues heading out of the neighborhood this morning.

 

Norm, would these causes be all of a sudden? It was fine this past Thursday and this morning as I was leaving the neighborhood. Also, is the governor located on the right rear of the transmission?

 

Can occur all of a sudden yes - especially if the modulator valve line fell off.
Governor & cover on driver side front of trans. Go to 10:30 on the video.

 

The good & the bad of a governor plastic gear. Not saying this is your issue, but they wear out. Sometimes they break, not often.

 

Dave - Ha! I said driver side front, it's passenger side rear - complete opposite. Too early for me, brain is off by 360° - more coffee.

 

Rubber vacuum hoses can split and then leak, causing a sudden problem.
The vacuum modulator line that connects the engine's intake manifold vacuum to the transmission's vacuum modulator is usually a metal tube with rubber hose connections at each end.
Vintage Chief's advice is right on track - check the rubber hose connections on the vacuum modulator line. The transmission won't up shift properly without this vacuum connection.

 

Will do...the modulator is where the hoses connect, right? Right side of the trans just behind the bell housing?

 

Modulator pipe location

 

Hard metal modulator pipe is routed from modulator valve (rubber end piece), snaked alongside the right-hand passenger side up to the intake manifold where it meets a rubber hose which is then connected to an intake manifold port.

 

I think that's more like 180 deg off. Have another cup.

Happy Father's Day all!

 

OMG. Hell yes. And, I'm off to fire up my chain saw. I may need the entire pot!

 

I dunno...I checked the fluid and it was good, all vacuum lines are good, 15" vacuum so no leaks. I disconnected the kickdown switch and after a couple times from a stop, it was good. Took it to get gas about 5 miles from the house and still good on the way home. Stopped after I got back into the neighborhood and hooked the kickdown switch up. Still good...drove around the neighborhood and did several stops, still good...I dunno. Maybe the kickdown switch was stuck?...but if it's not acting up, I can't diagnose it...lol

 

It was all just a bad dream...