Distributor and Distributor Vacuum Advance

[jbento]

Howdy!

A couple of relatively straight forward question regarding the above topic for a 1940 Series 72.

I know I need to rebuild the vacuum advance.

1) Can the vacuum advance be rebuilt separately, without having to rebuild the distributor, or must the be worked on and "tuned" together?
2) Can the vacuum advance be rebuilt at home, or is this something requiring a special expertise?
3) Is there a modern equivalent for this vacuum advance that can be swapped out for it, or is rebuilding the current one the only option?

Any suggestions or experience with who does this work?  I'd love to hear it.

[Steve Passmore]

Hi J,  The advance can be removed from the distributor, theres a small screw on the breaker plate that releases it along with the one or two screws on the outside of the body.  These cannot be rebuilt as the metal is peened over during assemble in the factory and the diaphragm rubber is not a listed part.  You can use a different one as long as you have the correct arm shape and length and pipe fittings are similar. I have used a more modern one before now, cut the arm off and soldered the original arm to the new one to give the correct length and fitting.

[harry s]

Joe,  Terrell Machine in Texas rebuilds those. Each time I have ordered from them they enclose a flier for that service. Not sure what the cost is, but as Steve says, it is not an easy job to be done at home.  Harry

[jbento]

Thanks!

I will contact them and see what they can do!

I appreciate the info!

[Jay Friedman]

Also, there is a company in Oklahoma, Special Interest Autos, that sells vacuum advance mechanisms--I think both new and used. 

As a previous poster said, it's important that you use the same model advance mechanism designed for your car's distributor or install the arm of the right length from another unit.  While a different model with a different arm length will fit and seem to work, if it's arm is a different length the distributor breaker plate will not be advanced or retarded correctly either for starting or running and the motor won't run right. 

[Caddy Wizard]

A vacuum advance unit can be rebuilt at home, if you are careful and take your time.  Here is a description of how I did it on a 1956 Cad.  You will need a bit of thin rubber sheet or neoprene.


My vacuum advance unit was completely shot -- no advance and the thing is a pure vacuum leak.  Fortunately, the vacuum unit on the modern-style '56 distributor is the same basic design that GM used for decades to follow. So while the exact fit unit is no longer available (spring rate and screw connection to vacuum), I was able to take my original apart and use the guts from a common later unit (that I also took apart). The diaphragm and its attached rod are EXACTLY the same as my original. The Echlin unit I got from NAPA for this purpose is VC1765. Cost about $10 -- works perfectly. My old unit is now absolutely as good as new.   The following is how I did it.

 

To do this, I clamped the old unit in a wooden vise, using a pair of wooden blocks to grip the stem of the housing.  I cut a V-groove in one of the blocks to receive the movable shaft (the actuator rod).  With the unit securely clamped in the vise, I carefully prised open the "can" using a small custom-made chisel.  I took a narrow pin punch and sharpened the end into a skew chisel and bent its shaft to work around the curvature of the canister a little bit.  Using this very narrow skew chisel, I started to work my way around the bent-over lip of the canister.  Once I had a little length of it prised up just a tad from the cover, I took pliers and bent it up straight, a little at a time, working my way around the cover.  Be careful, as at a certain point the cover will come loose and the spring will pop it up in the air.  Then it was a matter of cleaning the inside and discarding the old diaphragm/rod assembly.  I followed the same procedure to harvest the diaphragm/rod assembly from the new VC1765 and installed it in the old canister.  Then I buttoned it up by gently folding over the edge of the canister over the cover by gently tapping it with a very small hammer, again working a little at a time.  In the end, it looks just about perfect and works as good as new.



Art Gardner