Gas in oil / Modulator Valve?

I have just acquired this 51 Chieftain Deluxe 4dr sedan. I had went through and replaced the fuel lines, cleaned the tank, tore the 2bbl Carter carb apart also tore the non working fuel pump apart and cleaned both the carb and dual diaphragm pump. The oil in the car was super thin from gas getting into it somehow? The trans (original, not sure of the speed) wouldn't go into the higher gear all of the time (more not often than often).

Motor purred like a cat up until I had pushed the motor a little to see if the shifting problem was vacuum related.

Motor has picked up a knocking noise while under acceleration but goes away after shift.

What could be the problem there? Rod, Valve, Lifter???

Trans just doesn't seem to want to shift to higher gear or over drive if there is.

Is there a modulator valve or vacuum lines to control this trans? TV linkage seems to be fine with very little play.

Any help would be greatly appreciated as there is very little information out there on either the Pontiac straight 8 or the early Hydra-Matic.

Thank you in advance and thank you for accepting me into this forum.

No vacuum modulator on the old GM Hydramatic. The shifts are controlled by throttle position and road speed. Although the selector only shows Dr and Lo it is a four speed transmission. It should shift up and down automatically through all four gears. With light pedal pressure it should hit fourth gear at or before 45 mph. Late shifting could be caused by improper throttle rod adjustment or maybe sticking or rusted governor weights in the transmission due to inactivity. Maybe you could isolate the knock by zooming the engine and pulling plug wires one by one. A bad rod bearing would knock less when you pulled the wire on that cylinder. The thin gassy oil is probably a factor.

Which way do I adjust TV for earlier shift. More rod up or more rod down? It seems to completely miss 2nd gear all together. Also, what would cause gas in the oil? The fuel pump works like a champ but I do know that both diaphragms are brittle on the edges.

Many pages of information on the early Hydramatic in old Motor's Manuals, my 1950 edition has 26 pages of info on it. And plenty of info on the Pontiac in-line 8. Get yourself a copy, they are not at all uncommon or hard to find.

Most likely cause of dilution of motor oil by gasoline is a ruptured diaphragm in the fuel pump and if you are using an electric pusher pump the problem can be very much worse. Find the cause and fix and by all means don't run the engine at all until fixed, and drain and replace the oil.

Thanks Owen, I am going to check it out

Change the gassy oil before going further. The throttle lever on the side of transmission swings to the rear at idle. Pulling it forward by stepping on the gas raises the shift speed. If you adjust the rod to pull it less it should shift earlier. Count the turns you make so you can return to the original setting if it doesn't work right. You might want to screw a mechanical oil gauge into the oil sender hole in the block to see what kind of oil pressure you have especially after the engine is warmed up. If you don't trust the fuel pump run the car off a gas can hung up for gravity flow.