VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Vacuum shift, again

HELP! I have a 1940 chev special deluxe conv that started shifting hard in the spring. I have since adjusted the clutch, lubricated the vacuum can, it seems to have plenty of air movement by moving the shaft back and forth. I have replaced all the hoses and disassembled the vacuum piping back to intake manifold and cleaned everything and re-installed. I have disconnected wiper motor and vacuum lift cylinders (which work fine) and nothing changed. I’ve checked all of the linkage and nothing seems to have moved, I’ve even drained oil in trans and replaced that as well. No luck.

With motor running car not moving it shifts very nicely through all gears, take it on road and it won’t shift out of first gear. It feels stuck, but stop car and it will shift fine. Trying going again, it won’t shift out of 1st gear.

Not sure I can help with a post but there is a good description of how to adjust this vacuum canister in the original 1940 chevy manual - a must for 40' chevy owners! Sounds like an adjustment problem to me.

The key is this case is to determine if it is a vacuum shift problem or a transmission mechanical shifting problem.

A simple test is to start driving the car in second gear and try to shift to third as you normally would. If that shift is difficult to make then I would expect that the vacuum shift needs adjustment. They work great but are very sensitive to adjustment.

If it is easy to shift from second to third then I would start looking at the shift linkage, especially the linkage for first and reverse as well as the shifter box that is on top of the steering column.

Another test is to apply vacuum manually to the line the goes from the manifold to the shift canister. If that will not hold a vacuum then you have identified at least one problem. I use one of the Mighty-Vac hand pump tools to do checks like this.

Sounds more like a trasmission problem.

I agree with Gene. That is why I suggested testing the 2 to 3 and 3 to 2 shift. If those go well then the transmission or mechanical linkage is suspect.

So after adjusting everything related to vacuum shifting I still could not get it out of first while driving, so I disconnected the vacuum shift and installed the conversion kit to manual, and have same problem, so I guess I have a transmission problem not a vacuum shift problem. I have a few transmissions in stock, may rebuild one prior to installing, nice winter project. Thank you everyone.