My '68 C4 starts out in 2nd (not 1st) and shifts to 3rd when in "D". When 2nd is selected it starts and stays in 2nd as it should. When 1st is selected it starts in first and stays there until shifted to 2nd. Manually it shifts 1-2-3 and reverse,neutral and Park work fine.
I removed and cleaned the valvebody and checked the one-way clutch which would only turn in one direction as it should.After re-installing the valvebody and adding new fluid the car still starts out in 2nd when in Drive but shifts 1-2-3 when manually shifted.Nothing changed.
With the vacuum to the modulator disconnected it starts out in 1st when in Drive which is very strange. I couldn't get enough RPM and road speed to get it to shift to 2nd with the vacuum line disconnected in "D" but it did shift to 2nd when shifted from "D" to 2nd.
Cant be a sprag. It the sprag was bad you would have a neutral condition at a dead stop in drive. To start off in 2nd when in the D position the front band has to be applied so that is a governor or valve boby problem.I suggest you take another look at the valve boby and make sure the modulator valve isn't in backwards and the mod pin is in correctly. Check the valve end plate on the valve body to be sure it is on tight. Loosen all the end plate bolts, tighten the valve body bolts then retighten the end plate bolts.Chck to make sure the TV limit valve and spring are installed valve first then spring. Make sure you have the right gasket in the valve body the gasket can not cover up any holes in the seperator plate. If you dont see anything there check out the governor. Make sure the valves are free and that it is not on backwards.
Thanks for the input Mac. The valvebody and all the valves checked good.The trans has been working fine for a few years and just started having the noted symptoms.The govenor is suspect as you mentioned. Maybe with the vacuum line removed from the modulator the line pressure was raised enough to overcome the false signal from the govenor allowing a first gear start in D? The govenor air check resulted in a "farting" sound from the in and out ports. Is that normal?
It's a '68 trans and valvebody with a TransGo 47-2 kit.
The motor had to come out to get the trans out and the tailshaft housing off. The primary valve was stuck open causing the auto shift problem. Somehow the valve was stuck in the spring seat washer which was halfway out past the snap ring. Maybe the governor didn't like repeated 6000+RPM output shaft speed at the track and jammed opened? Probably not. Thanks for the help,guys.