Packard Forum Index » Pre-War (1899-1942)

Going through the Technical Letters provided here by BigKev, I found the answer to the question of the so-called "vent filter." Turns out a more accurate term for the pictured part would be "shock oil reservoir."

Packard shocks circa 1930 apparently had an oil leakage problem when the shocks were "working hard" and the oil got hot and expanded. The first attempt to remedy the repercussions of this was a new vented filler plug described in Technical Letter #1880 dated 10/29/29. It allowed oil to escape through a vent hole in the plug rather than around the packing gland and metering valve, thus (hopefully) preventing air replacing oil in the interior when the shock cooled thereby "changing the action of the absorber." The plug was fitted with a felt packing to "filter" dust and dirt from entering the shock. The new plug may thus have been more or less accurately called a "vent filter."

Apparently, this remedy was inadequate - at least for very hard driving - as oil lost was now being replaced by air entering through the vented plug. Customers continued to complain the shocks would not "stay put", therefore a device was designed which prevented air from entering the shock body by interposing a reservoir of oil between shock and vent. The reservoirs could be ordered as a factory add-on option and are described in Technical Letter #1903 dated 8/1/30. It does not appear these were ever standard equipment, so they are possibly rather unusual.

It isn't surprising these shock reservoirs were necessary and eventually installed on my 740 as it was purchased new in Utah and frequently driven on rough, unpaved mountain roads in the southwestern part of the state for commuting to and from a family ranch.