Re: 1953 Delco Vacuum Advance

Posted by DavidPackard On 2023/9/1 21:32:05

53 Cavalier

There are only two possible configurations of shims for the vacuum chamber.

First is the type that fits between the vacuum port fitting and the chambers housing. That would be somewhat like the oil drain plug gasket . . . quite visible once installed. Shimming the fitting further away from the housing will reduce spring preload and reduce the amount of vacuum to achieve both test points. There will also be a gasket to seal the chamber in this location, and the shims could be multiple gaskets.

Second is the type that positions the shim between the spring and the fitting. This shim would not be visible once installed. Adding shim material in this location will increase the spring preload and increase the amount of vacuum to achieve both test points. The fitting gasket must also be retained when internal shimming.

In both cases I’ve included a description of adding shims. If shims are removed the opposite affect occurs. If you think of a plot of applied vacuum versus arm position, shimming will translate the curve up/down or left to right. Shimming will not change the slope of the line.

dp