No less than three different mirror arms were used on Advance Design Trucks (1947-1955). Though most vendor catalogs do not reflect these differences, the following should be of interest to those that want their truck restored correctly.
All left mirror arms attach to the same position on the cowl, however two designs were used. In the beginning years (1947-50) the arm pointed at an upward angle. This was much like earlier GM truck body styles between 1936 and 1946.
A change in design began in 1951 with the introduction of door wing vents. With the vent and door open together the mirror head could be hit and broken. Thus, a more horizontal arm was designed and it lowered the mirror. The rounded corner of the wing vent frame could no longer touch the mirror glass.
The right side cowl mounted mirror arm was a dealer installed accessory. Because of the limited space on the cowl (between the door and hood) it was necessary to place a curve in the arm. This brought the mirror head forward so that it could be seen through the lower right corner of the windshield.
1947-1950 Left (MI108) (above)
1951-1955 Left (MI109) (above)
1947-1955 Right (MI125) (above)