I just recently purchased a 77 vette. The tranny is an automatic and doesnt seem to shift in drive. Its one speed constant should there be another gear maybe a vacuum off ? Any help welcomed.

 

If it's stock,it's a Turbo 350 and has 3 gears. It won't shift if the vacuum modulator is disconnected. You might be able to force a shift by holding it in low until 25 mph or so and then shifting up. A 350 pan is about square with on corner cut off at an angle.
Ron

 

I carried it to a local guy to look at it and thats what it is. I am used to cars with an overdrive and this does not have one. It shifts quick and I have been waiting on the od to kick in. I guess I have forgotten my younger days. It has a holley high rise and a 650 holley four barrell and will scream down the road. I had been waiting on the shift and it wasnt there. Well now I know why. Thanks again.