First of all, there were two types of oil pumps on the 1955/56/57 Thunderbirds. The 1955 models and most 1956 models had the gear type pump, part number B5A 6600 B, which had cast iron housing and bottom cover, Photo # 1.
Late in 1956, it was replaced with part number B6A 6600-A, a rotor type pump which had an aluminum body and steel plate bottom cover, Photo # 2. Product Service Letter number 729 dated September 18, 1956, introduced the new aluminum pump. It is not known how many of the aluminum rotor type pumps were actually installed on 1956 models since the pump showed up late in the 1956 production year. All 1957 models had the aluminum type rotor pumps, original part number B6A 6600 A.
The part numbers B5A 6600 B & B6A 6600 A for this article were obtained from the 1955/1956/1957 Parts and Accessory Catalog. The later 1949-1959 Parts and Accessories Catalog Shows the aluminum rotor pump part number changed to be C0AE 6600 D and was used as a replacement service part for all 1955/1956 models as well as standard equipment on 1957 models. Although the part number changed the aluminum rotor pump remained the same.
Now to a problem that can occur when attempting to stop an oil leak around the bottom access plate. I had a car in my shop that someone had replaced the seal on a rotor type aluminum pump with a thicker O-ring seal, Photo #3. The results of the thicker O-ring seal fixed the leak, but had also added clearance between the pump rotors and the bottom access plate causing the oil pressure to drop at engine idle speed. The drop in oil pressure caused the indicator lamp to flicker.
The early cast iron pumps do not have an O-ring seal, they have a paper gasket. If a thicker gasket or double/triple gaskets are installed it can also increase the clearance between the inside pump body and the gears resulting in low oil pressure at idle speeds.
For more information on rebuilding the aluminum rotor pump and rebuild kit part number go to www.ctci.org, CAR TECH, Gil’s Garage, then the Engine section, you will find a how-to article on rebuilding the aluminum rotor type pump.
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