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Fuel Pump Overhaul

By Stephen Kassis



With the alcohol that has been added to most of our gasoline, fuel pumps are often the first part on the engine to suffer. Alcohol attacks the old style rubber diaphragm materials that were not alcohol resistant. This can cause fuel pump failure. If you have purchased a New Old Stock (NOS) fuel pump, it is recommended that the diaphragm is replaced before attempting to use it.

Another problem is that the new alcohol gas tends to break down faster than non-alcohol gas. This can cause problems due to the gummy substance that is formed when the fuel breaks down. It can plug fuel lines, fuel pumps and carburetors. In addition, it can cause intake & exhaust valves to stick, causing bent pushrods and other problems.

Fortunately, fuel pumps on early Chevrolet 6-cylinders are easy to rebuild. If the fuel pump fails to pump fuel, it does not mean that the pump is bad. The first thing necessary is to make sure that there is fuel is getting to the fuel pump. Is there fuel in the tank? Sometimes the fuel gauge may not read properly or there is something plugging the fuel line. The pump may be fine but cannot pump fuel because fuel is not getting to the pump.

It is also possible that the camshaft fuel pump lobe is worn to the point the fuel pump lever will not operate properly. This is a more serious problem and could require replacing the camshaft. To test the fuel pump, remove the front fuel line that goes to the carburetor. Remove the two bolts that hold the fuel pump to the block. This will allow the fuel pump to be removed from the block and pumped manually. If no fuel will pump manually, remove the fuel pump from tank feed line.

If there is a good amount of fuel in the tank, fuel should gravity feed from the tank to the fuel pump connection when the line is lowered below the level of the tank. If no fuel will flow with this test, remove the gas cap and have someone listen a few feet away from the opening while pressurizing the fuel line with compressed air in short bursts. CAUTION: fuel may gush out of the filler neck when doing this test. Keep everyone a few feet away from the opening. If air bubbles are heard when sending compressed air back through the line, then there may have been some foreign matter that is in the tank plugging the fuel outlet. Recheck for gravity feed of fuel.

If the fuel line is clear then further testing of the fuel pump is necessary. Place the inlet side of the pump into a pan of water and manually operate the pump lever. If water is not pumped out with this manual method, it will indicate that the pump should be rebuilt.

Original fuel pumps on Chevrolets were made by AC. Somewhere on the pump should have raised “AC” cast into it. If your pump has no markings on it or it has “BC” or other brand names, original fuel pump kits may not have the parts required to rebuild it. If you have an AC pump, obtain a fuel pump rebuilding kit. It should contain: New valves, alcohol resistant diaphragm, cam springs, cam cover gasket, glass bowl gasket and fuel pump to block gasket. Other parts may be included, but these are the minimum that should be in the kit. Drain off any gas remaining in the fuel pump. Remove the glass bowl & wire bail that holds it in place. Remove the 6 screws that hold the top and bottom parts of the pump together. Separate the top and bottom halves. The top half should hold the valves. On early pumps (1929-1936) these valves are inside of a brass hex fitting. Remove the fittings carefully as there is a fine spring inside each one. Remove the hex shaped flat Bakelite valves.

On 1937 and later fuel pumps, self-contained valves replace the earlier design. These valves are removed by removing the valve retainer and screws. The lower half of the pump differs in design depending on the year of the pump. Early pumps (1929-1933) have a diaphragm that is held with a simple nut, flat washer & lock washer. These are easily removed. From 1934 and later, the diaphragm is fixed onto a shaft. This type of diaphragm must be replaced as a unit.

Drive the lever arm pivot pin out sideways. CAUTION: Some pump housings have a tapered pin and must be driven out the large end or damage to the housing may result. Once the pump has been completely disassembled, clean all the parts in solvent.

With all parts clean and ready for assembly, start with the lower half of the pump. Inspect the lever arm for damage or wear. If worn, a new arm should be installed. Install the new diaphragm making sure that the holes in the diaphragm match up to the lower housing holes. Install a new gasket on the pivot shaft cover (early pumps only) and install new shaft springs at the same time.

Install new valves in the upper half. On 1929-1936 pumps, a drop of light oil on the Bakelite valve is recommended. This will help insure good operation until fuel gets to the pump. On 1937 and later pumps, the inlet valve has the spring facing downward and outlet should have the spring facing upward. Install the valve retainer with convex side up and a new gasket for the glass bowl. Do not over-tighten the bail as it may damage the die cast pump housing. Assemble the top and bottom halves of the pump together with the 6 screws. Insure that the housings are matched properly and diaphragm lines up before screwing them together.

With everything assembled, it is time to test the rebuilt pump. Put the inlet side into a pan of water and pump the lever arm manually. You should see the glass bowl fill quickly and, once full, water should start shooting out the outlet side. If everything is working properly, a stream of 4 to 8 feet should come out of the outlet.

If the fuel bowl fails to fill, loosen the glass bowl slightly and turn it, then re-tighten. If this gasket leaks, the pump will only pull air. If everything tests out correctly, remove the glass bowl and blow out any excess water. This would be an excellent time to install a paper element filter inside the glass bowl. Paper element filters do a much better job of removing particles from fuel than the original screens used in these pumps. We strongly recommend the use of this type of filter, unless you have a separate inline filter.


Related Parts

FS-371 - 1929-1933 Fuel Pump Diaphragm

RW-717 - 1916-1960 Carburetor & Fuel Pump Fitting

FS-607 - Glass Bowl Gas Filter Assembly

FS-607AC - "AC" Glass Bowl Gas Filter Assembly

FS-235 - 1929-1933 Glass Bowl Fuel Pump Paper Filter

FG-4 - 1952-1957 Glass Bowl Fuel Pump Paper Filter

AF-429 - STA-BIL Fuel Stabilizer 4 OZ

AF-429B - STA-BIL Fuel Stabilizer 32 OZ

AF-3 - B-12 Chemtool 16 OZ Aerosol

PA-67 - POR-15 Fuel Tank Repair Kit

H-19 - Fuel Tank Repair Kit

PA-61 - POR-15 Gas Tank Sealer - Quart

H-3A - Alcohol Resistant Gas Tank Sealer