VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 33 Master Vacuum Advance

Looks like my Vacuum Advance on my Distributor is not working. I think I had this problem before but don't remember how I fixed it. Any suggestions?

This is long but I hope the explanation makes sense. I’m guessing it will work for your 33.

The vacuum advance on my 34 Master quit working and finding a replacement was difficult. While I was looking, I thought I’d have nothing to lose if I attempted a repair. Since the defective unit could be stroked freely by hand, I assumed the diaphragm had ruptured. If you look closely the advance, the two halves are joined around the perimeter with a tight crimp. After some effort with a sharpened screw driver and slip joint pliers, I was able to separate the two halves taking care not to overly damage the mating surfaces. Inside is a spring and the diaphragm with the actuating tab riveted to it. I carefully removed the actuating tab from the ruptured diaphragm by grinding off the rivet. I had a new spare vacuum advance from a 60’s 6 cylinder of the same diameter. After disassembling the new spare, I used its diaphragm in the 34 by replacing its tab with the one from the 34. Rather than riveting the tab, a small nut and bolt worked great. Prior to crimping the two halves back together, I used a small amount of black rtv on the outer edge of the diaphragm.

As a side note, I think the starterator vacuum unit can be repaired the same way.

Great suggestion. How do I know if the diaphragm is ruptured before I tear it apart?

Remove the unit from the distributor and actuate it by hand with your finger over the vacuum connection. If the diaphragm is good you should be able to hold it in the stroked position until you remove your finger. You might be able to accomplish the same without removing by disconnecting the tab and and the vacuum connection.

Thanks, I'll try it later.

Well, I tried that. Looks like it holds the same as my 35 so something else must be the problem.

Jon, If the vacuum advance unit itself strokes freely and holds vacuum, I can only think of a low vacuum supply to it or some type of binding in the distributor. You could see if it moves with the vacuum line connected but the actuating tab disconnected from the distributor. Mike

OK, I'll look today.

Looks liek it is free but does not advance when I accel. the car.

Connect vacuum gauge to the end of the vacuum line where it attaches to the distributor. There should be a vacuum reading on that line when you open the throttle a little bit. That exposes the vacuum port on the carburetor to vacuum.

I'll do that tomorrow, if I can find my vac. guage.

I found my vac. gauge. Disconnected the line going to the dist, and some vac. so tomorrow I'll hook up one of my vac. pots which say they are good and see what happens.

Note that you will not have any vacumm at idle speed.. The vacumm port in the throat of the caburetor is not exposed to the vacumm in the throat f the carburetor at idle speed.

Got my Vac. advance working today. Seems like maybe the problem I had was the "Pots" that I installed were not working even though I thought they were. Now we'll see if the car starts in the morning although I don't think the vac. advance had anything to do with it not starting after sitting over night. I'm going to get this mystery solved or hang myself which ever comes first.

I think I found the problem. The choke flapper or whatever it is called is in the Carb. is upside down. So when you choke it it really dosen't get full choke. So when you prime with gas it increases the fuel mixture and it starts. I'll take the carb. off tomorrow and fix the flapper and I'll bet it will start.

Took the Flapper out and turned it around. Put Carb. back on and it started like it should. Problem solved!

Very good! Thanks for sharing your success.