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I have two cylinder heads for my 740. The spare is clearly a 1930. The one that was installed on the car is evidently off a later year as it uses 14mm plugs and has "HC" stamped on it. This head also has a three-bolt distributor to head mount instead of four bolt as used with the 1930 head.

My question is what year did Packard switch from the four to the three bolt mounts, and did the 1932 mounting bracket change in design from the one used on 1930. I ask this because the mounting bracket on my 740 is the same two-arm style as used with the 1930 Northwest 10868 distributor, yet it differs from a typical 1930 bracket in that it mounts using three bolts instead of four. From what little I have been able to glean from photos on the web, the mounting bracket used in 1932 is of a different design, perhaps with only one arm.

EDITED.

Can't pin down exactly but the dual coil Northeast setup for Eight and Super 8s introduced in 1933 utiized the 3-bolt distributor mounting to the head.

I tracked down a high-res photo of a 1932 engine. It appears the three bolt mount was being used that year. The mounting bracket is very different from 1930, however, in that it is shorter and lacks the two arms and the spark advance plate.

Unless there was a crossover period, the apparently hybrid mount my car has could otherwise only be explicable as a part available for those who wanted to convert to a later HC head.

A manual spark advance linkage is not evident in the attached photo of a 1932. Did Packard use manual spark advance after 1931? If so how was it linked up to the distributor and when was it finally discontinued in favor of vacuum advance?

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1933-34 Eights and Super 8s have full automatic centrifugal advance but no vacuum advance and obviously no manual advance.

The 1930-32 Parts book shows distributor control on the instrument panel in '31, but not '32, so 1932 must be the first year of full centrifugal advance. Of the two controls on the redesigned panel for '32, one must be choke. Is the other the new shock absorber control?

Prompted by Owen's comment I researched the introduction of vacuum advance in automobiles. I was able to determine it was first used sometime in the 1950s but not what the first make to use it was. I wonder if any Packard ever had vacuum advance.

I question your research sources, Packard and many others had vacuum advance well before WW II.

My '39 Six has vacuum advance.... Chris

When I googled vacuum advance or related terms, history of, and so forth, very little came up. Perhaps someone more computer savvy would have better luck. All I could find was a reference to it being on cars since the '50s. Thanks for clarifying it is on '39 Packard, Chris.

Sherlock, I see what you mean; I tried Googling "vacuum advance' numerous different ways and the info seems a little spartan alright. Saw one thread that says the first Buick to have V.A. was '32, but nothing as far as the year it was 'invented' or developed, nor it's advent of common usage in the automotive industry. My own 'educated guess' would be early 30's??? Chris.

In pretty wide-spread use by most automakers by 1935-36.