GMC V6 Fuel Pumps comparison, rebuilding kit and swapping
Quote:
Clarke:
Now, there has to be a reason why GMC changed the fuel pump design, making the fuel pump body/diaphragm larger diameter and bending the arm… My theory is, the bent arm reduces the amount of travel on the diaphragm; therefore, reducing the amount of stress/stretch on the rubber diaphragm. Furthermore, due to the shorter (arm) travel, GMC increased the diameter of the fuel pump body to increase the surface area for sufficient pump/vacuum, then increased diameter of fuel line to increase fuel volume.
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Reading this it got me thinking about rebuilding my old fuel pump from a 1962. It has the straight lever and not the bent lever and secured with 10 bolts. I believe Clarke is correct, that the bent levers were an update to reduce premature fuel pump failure. His thoughts on Ethanol fuel not necessarily being the culprit, but excessive, extended RPMs, made sense.
Trying to find a rebuild kit for the GMC unit that could be rebuilt, was a discovery. I found a kit from a company called, Then and Now, #FPA-225, which is for a GMC V6, but it doesn’t have the pressure spring. Cost is $52.50 plus about $12 for the spring.
Top Flight also has a kit that with the Pressure Spring that look’s more correct for my pump and runs $100. It’s listed for a 55-66 Corvette so maybe that’s the reason for the high price. Still cheaper to buy a new one but wait…
I researched and found the Corvette style pump, with the ten bolts, and it looks like a regular pump for a six cylinder Bel Air. It was cheap, about $30 and it weighed less, but it matched up, so I swapped the lower bowl and changed out the upper Diaphragm and reassembled. I could have just swapped the lever, but chose not to do that.
I also purchased the Carter M3955 for comparison. It has the straight lever and is much small and lighter with smaller inlet and outlet holes.
Also purchased a Carter crimped style, bent lever, fuel pump M4548 mentioned in the above thread.
Lots of tutorials online on how to rebuild a fuel pump and it’s a fun project. But as an alternative to the kit, I just decided to swap out parts from a newer unit.
The Carter Electric fuel pump (4070?) I used for many years, is now manufactured overseas. I have been reading about premature failures for these units, and it was suggested to buy NOS with “Made in the U.S.A.” stamped on them.