The Definitive Guide to the 1940 Ford Fuel Pump: Restoration, Repair, and Replacement

The mechanical fuel pump is the vital heart of the 1940 Ford's fuel delivery system. Properly functioning, it reliably delivers fuel from the tank to the carburetor under precise pressure. Understanding its operation, recognizing symptoms of failure, knowing how to replace it correctly, and ensuring compatibility with modern gasoline are essential for maintaining the performance and drivability of your cherished 1940 Ford. Whether you're dealing with a sudden stall, reduced power, or undertaking a comprehensive restoration, mastering the details of the 1940 Ford fuel pump is non-negotiable.

Understanding the 1940 Ford's Mechanical Fuel Delivery

Unlike modern vehicles relying on high-pressure electric fuel pumps, the 1940 Ford, like most cars of its era, employed a simple yet robust mechanical pump. This pump is physically mounted directly to the engine block, typically on the passenger side of the Ford Flathead V8. The core principle relies on engine motion for operation.

• The Lever Arm: A lever arm protrudes from the pump body. This arm rests directly on an eccentric lobe on the camshaft inside the engine.
• Camshaft Activation: As the engine rotates, the camshaft's eccentric lobe moves up and down. This movement pushes the pump's lever arm up and then allows it to return down under spring tension. Every rotation of the camshhaft (which occurs for every two rotations of the crankshaft) generates one complete pump cycle.
• The Pump Cycle:
  • Downstroke (Suction): When the cam lobe pushes the lever arm up, an internal diaphragm inside the pump is pulled upward by linkage connected to the arm. This upward movement of the diaphragm creates a vacuum (low pressure) within the pump chamber below it. This vacuum draws fuel from the gas tank, through the fuel line, past the inlet valve (which opens due to the vacuum), and into the pump chamber.
  • Upstroke (Pressure): As the cam lobe rotates past its peak, the spring tension forces the lever arm down. This pushes the diaphragm downward. This downward movement pressurizes the fuel trapped in the chamber below the diaphragm. This pressure closes the inlet valve to prevent backflow and forces open the outlet valve. The pressurized fuel is then pushed out through the outlet port, up the fuel line, and towards the carburetor.
• Regulation: The pump's internal spring determines the maximum pressure it can generate. A typical operating pressure range for a stock 1940 Ford fuel pump is between 2.5 and 4 psi – sufficient to feed the downdraft carburetor without overwhelming it. Excess pressure above what the spring can contain would bypass internally, though severely weakened springs cause pressure loss.

Core Function and Importance

The 1940 Ford fuel pump has one critical job: maintaining a steady supply of fuel at the correct low pressure to the carburetor's float bowl. The carburetor relies on this consistent supply to meter the correct fuel mixture into the engine's intake manifold. Without this reliable flow at the proper pressure, engine performance suffers immediately and dramatically. It is a critical link between fuel storage and fuel consumption within the engine.

Early Symptoms of 1940 Ford Fuel Pump Failure

Mechanical pumps are generally reliable, but diaphragms age, springs weaken, and valves stick or leak. Recognizing early warning signs can prevent roadside breakdowns:

1. Engine Stalling, Especially Under Load or Uphill: One of the most common signs. As fuel demand increases (accelerating, climbing hills), a failing pump cannot deliver sufficient volume, causing the engine to suddenly lose power and stall. Restarting might be immediate or require a few minutes for fuel to slowly seep back into the carburetor bowl.
2. Reduced Power and Hesitation: A general lack of power during acceleration, or a noticeable "hesitation" or "flat spot" when pressing the throttle, often indicates the carburetor bowl isn't filling fast enough due to insufficient pump output.
3. Hard Starting After Sitting: If the car starts easily when cold but is difficult to start after sitting for 30 minutes or more (particularly on a hot day), it can point to a weak pump or excessive fuel pressure loss (leak down) when the engine is off. This allows the carburetor float bowl to drain partially, requiring excessive cranking to refill before starting.
4. Engine Sputtering at Higher Speeds: Similar to stalling under load, sustained high speeds place maximum demand on the pump. A failing pump may cause sputtering or a noticeable power loss that resolves when slowing down.
5. Visible Fuel Leakage: While less common than internal failure with modern pump bodies, seepage of fuel from the pump body itself (around the seams, gasket, or sediment bowl) is a clear and urgent sign of failure. Even minor drips are a significant fire hazard and require immediate attention.
6. Oil Dilution (Extreme Cases): If the diaphragm develops a pinhole leak, gasoline can seep into the pump body cavity below it, which is connected via weep holes to the crankcase. This gasoline contaminates the engine oil, leading to thinning, reduced lubrication, and potential engine damage if driven extensively.
7. Constant Vapor Lock Issues: While often related to fuel line routing and modern gasoline, an exceptionally weak pump can contribute significantly to vapor lock problems, as it doesn't generate enough pressure to overcome vapor bubbles forming in the fuel line.

Diagnosing Fuel Pump Issues on Your '40 Ford

Before condemning the pump, perform some basic checks:

1. Visual Inspection:
   • Check for any signs of fuel leaks around the pump body, sediment bowl seal, and inlet/outlet connections.
   • Examine the fuel lines from the tank to the pump and from the pump to the carburetor for kinks, sharp bends, rust, or physical damage that could restrict flow.
   • Ensure fuel filter(s) are clean (many '40s have in-line glass filters or use the sediment bowl).
2. Sediment Bowl Check: Remove the glass sediment bowl underneath the pump. Inspect it for excessive debris, rust particles, or water. Clean it thoroughly. Check the bowl gasket and replace it if hardened or cracked. Verify the mesh screen inside the sediment bowl chamber is not clogged.
3. Carburetor Fuel Level (Check Sight Glasses): Most original Ford carburetors (like the Holley 94 or Ford 81/91) have glass sight plugs on the side of the float bowl. With the engine idling, the fuel level should be close to the center dot or line on the plug (consult a specific carburetor manual). A significantly low level at idle indicates a pump delivery problem, assuming the carburetor's float and needle valve are functioning correctly.
4. Flow and Pressure Test (Recommended): This is the most definitive check for the 1940 Ford fuel pump.
   • Disconnect the fuel line at the carburetor inlet. Attach a short length of hose to the pump's outlet and direct it into a clean container (capacity at least 1 pint/500ml).
   • Have an assistant crank the engine with the ignition coil wire disconnected (to prevent starting) for 15-20 seconds.
   • Observe Flow: Good pump output should produce a strong, pulsing stream (due to the mechanical action) that fills the container relatively quickly. Weak or intermittent flow points to pump failure or a blockage upstream (tank pickup, fuel lines).
   • Measure Pressure: Insert a low-pressure fuel pressure gauge (range 0-15 psi) between the pump outlet and the carburetor inlet. Restart the engine and let it idle. The gauge should read consistently between 2.5 - 4 psi. Steady readings significantly below 2.5 psi or fluctuating wildly indicate a failing pump. Readings above 4.5-5 psi suggest a problem (potentially wrong pump variant or stuck bypass) that could overwhelm the carburetor needle valve, risking flooding.

Essential 1940 Ford Fuel Pump Specifications

Knowing these details is vital when searching for parts:

• Original Part Number: Ford 91A-9350 (or earlier pre-1940 numbers superseded to this). Modern reproduction pumps often cast this number on the body.
• Mounting: Bolts directly to the engine block on the passenger side. Mounting bolts thread into the block (not through into the timing cover on later models). Early Flatheads may have a slightly different boss.
• Fuel Ports:
  • Inlet (Suction): 5/16" inverted flare. Connects to the fuel line running back to the tank.
  • Outlet (Pressure): 5/16" inverted flare. Connects to the fuel line running up to the carburetor.
• Internal Pressure Regulation: Via a spring, calibrated to deliver 2.5 - 4 PSI.
• Diaphragm: Fabric-reinforced rubber compound. Modern ethanol-resistant materials (Viton/Nitrile) are crucial for longevity.
• Lever Arm Design: Unique to the 1940 Ford application. This arm must have the correct profile and arc to properly ride the camshaft eccentric. An incorrect lever arm will cause low output or damage. Many modern pumps replicate the 91A profile accurately.

Types of Replacement Pumps for the 1940 Ford

You have several options, each with pros and cons:

1. New Old Stock (NOS): Original Ford pumps from the era, never installed. While prized for authenticity, their diaphragms and seals are almost certainly deteriorated and unusable after 80+ years. Essential for concours restorations but must be rebuilt immediately with modern components (especially the diaphragm) before installation. Often expensive.
2. Modern Complete Reproduction Pumps: Widely available from reputable vintage Ford parts suppliers (Bratton's, MAC's, C&G, Dennis Carpenter, etc.). These are brand new pumps cast and assembled to replicate the original Ford 91A-9350 externally and internally.
   • Pros: Correct appearance, dimensions, and lever arm profile. Often come with ethanol-resistant diaphragms and valves pre-installed. Ready to run. Reliable.
   • Cons: Quality can vary slightly between manufacturers. Always buy from trusted vendors known for supplying parts for Flathead Fords. Price is moderate.
3. Pump Rebuild Kits: Kits are available containing a new diaphragm, valves, valve seat gaskets, sediment bowl gasket, and sometimes springs. Requires disassembling your existing pump core. Crucially, the core must be undamaged (no cracks or stripped threads) and have the correct 91A profile lever arm.
   • Pros: Preserves your original, numbers-matching pump core (important for judging). Cost-effective.
   • Cons: Requires mechanical aptitude and care during disassembly/assembly. Existing valves/seats may be too worn to seal properly with new valves. Old springs may be weakened. Ensuring an ethanol-resistant diaphragm kit is mandatory. Availability of high-quality kits is good.
4. "New" Stock-Style Pumps with Sight Feed: Some suppliers offer reproduction pumps that function like the original but feature a clear plastic sight feed tube mounted vertically. This allows constant visual verification of fuel flow from the outlet port. Highly functional for diagnosing future issues, though not strictly original in appearance.
5. "Sealed" Modern Electric Pumps (Not Recommended for Stock): Small electric pumps (e.g., Facet cube or cylinder style) delivering low pressure (~3-4 PSI) exist. These require wiring, switches, and safety precautions.
   • Pros: Eliminates reliance on cam lobe/lever arm wear. Can sometimes overcome vapor lock better if installed correctly near the tank. Potential fix if cam eccentric is worn.
   • Cons: Sacrifices originality. Requires significant modification (fuel lines, wiring, safety cut-off switch). Installation complexity. Potential fire hazard if improperly wired/fused. Overwhelmingly discouraged for stock 1940 Ford restorations unless all other options fail due to mechanical wear issues. Primarily a workaround.

The Critical Factor: Ethanol-Resistant Components

Modern gasoline blends contain ethanol (E10, E15). Ethanol is a powerful solvent that quickly degrades older rubber formulations used in fuel system components. The fuel pump diaphragm is particularly vulnerable.

• Old Rubber Diaphragms: Will swell, soften, disintegrate, or develop pinhole leaks within months when exposed to ethanol-laden fuel. This leads directly to fuel leaks (external or internal into the oil) and pump failure. NOS pumps and old rebuild kits contain these obsolete materials.
• Ethanol-Resistant Materials: Modern rebuild kits and reproduction pumps use diaphragms made from Nitrile or Viton (Fluoroelastomer). These materials resist ethanol degradation for significantly longer periods. Viton generally offers the highest resistance.
• Imperative: Whether rebuilding your original pump or buying a new reproduction pump, ensure the diaphragm is explicitly marketed as Ethanol-Resistant or made from Nitrile/Viton. Do not install a pump with unknown diaphragm material composition. This is the single most important factor affecting longevity. Reputable suppliers clearly state this feature.

Step-by-Step Guide: Replacing the 1940 Ford Fuel Pump

Replacement is generally straightforward. Gather parts and tools beforehand:

• Parts: New pump (or rebuilt original), sediment bowl gasket, pump-to-block gasket, possible inlet/outlet line gaskets (inverted flare copper washers).
• Tools: Wrenches (7/16", 1/2", 9/16" are most common), screwdriver (for sediment bowl clamp), container for fuel spillage, rags, safety glasses, jack stands (if needed for access), new engine oil/filter (if diaphragm leakage into oil is suspected).
• Safety First:
  • Work in a well-ventilated area.
  • Disconnect the negative battery terminal.
  • Relieve fuel system pressure by running the engine until it stalls from lack of fuel (if possible). Alternatively, clamp the inlet line near the tank and disconnect carefully.
  • Have a fire extinguisher nearby. Absolutely no sparks or open flames!

Procedure:

1. Drain Fuel: Place a container under the pump. Loosen the sediment bowl retaining screw/clamp. Carefully lower the glass bowl to drain any fuel into the container. Remove the bowl and its gasket. Set aside.
2. Disconnect Fuel Lines: Use appropriate wrenches to carefully disconnect the fuel inlet line and outlet line from the pump body. Be prepared for some fuel spillage. Plug the ends of the lines if possible to minimize fuel leakage and prevent dirt entry. Cap the ports on the old pump if removed.
3. Remove Mounting Bolts: There are typically two bolts securing the pump to the engine block. One is usually longer. Note their locations and any washers. Remove the bolts.
4. Remove Old Pump: Gently pull the pump assembly outward and downward, disengaging its lever arm from the camshaft eccentric inside the engine block. It may require slight rocking. Be careful not to bend or kink the lever arm excessively during removal.
5. Clean Mounting Surface: Thoroughly clean the pump mounting pad on the engine block and the surface of the timing cover (if applicable) using a rag and brake cleaner or similar solvent. Remove all traces of the old gasket material. Ensure the cam lobe is at its lowest point (lever arm retracted) to ease reinstallation. You may need to carefully rotate the engine using the hand crank or by pulling the coil wire and bumping the starter briefly (exercise extreme caution!).
6. Install New Pump Gasket: Place the new pump-to-block gasket onto the mounting studs/locating pins. Ensure the correct gasket (holes align). Use sealer sparingly if the gasket isn't a coated composition type – some experts prefer dry.
7. Position New Pump: Carefully maneuver the new pump into place, ensuring its lever arm is correctly aligned with and resting on the camshaft eccentric lobe inside the engine. This can be tricky and requires patience. Getting the tip of the arm to engage the eccentric correctly is crucial. The pump body should sit flush against the block.
8. Install Mounting Bolts: Start the bolts by hand to ensure threads engage correctly. Tighten the pump mounting bolts evenly and securely. Do not overtighten. Consult torque specs if available (typically around 20-25 ft-lbs for 7/16" bolts), but firm snugness is usually sufficient on a clean thread. The longer bolt usually goes in a specific position – note the old one.
9. Reconnect Fuel Lines: Attach the inlet fuel line to the pump's inlet port first, using a new inverted flare gasket (copper washer) if needed. Tighten securely. Then attach the outlet fuel line to the pump's outlet port, again using a new gasket washer if necessary. Tighten securely. Ensure no cross-threading occurs.
10. Install Sediment Bowl: Place a new sediment bowl gasket over the pump's sediment bowl base studs. Position the clean glass sediment bowl carefully. Install the clamp and secure its screw moderately tight – just tight enough to compress the gasket and prevent leaks, overtightening will crack the glass. Do not use the screw to pull the bowl up excessively.
11. Final System Check: Reconnect the battery negative terminal. Add clean gasoline to the tank if very low. Temporarily place a rag under the pump and connections. Start the engine and immediately check for fuel leaks everywhere: inlet/outlet fittings, sediment bowl seal, pump body seams, and mounting gasket. Smell for gasoline fumes! Repair any leaks immediately. Re-inspect several times during the first drive and again the next day.

Post-Installation Checks and Potential Issues

After installation, verify proper operation:

1. Fuel Level: Check the carburetor sight glass. With the engine idling, the fuel level should be stable around the center mark. Initial filling might take a few seconds of cranking or idling.
2. Performance: Drive the car normally, paying attention to power under acceleration and on inclines. Hesitation or stalling should be resolved.
3. Leaks: Conduct repeated leak checks after driving, as heat cycles can reveal new leaks.
4. Oil Check: If you suspect the old diaphragm leaked fuel into the oil (indicated by a strong gasoline smell in the oil or elevated oil level/dilution), change the engine oil and filter immediately after replacing the pump. Driving with fuel-contaminated oil can cause severe engine damage.
5. Priming (If Required): Some pumps "self-prime" immediately; others may require the engine to crank longer on the first start to draw fuel up from the tank. Excessive cranking without starting could indicate an installation problem (incorrect lever arm positioning/engagement, major leak, blocked line). Double-check your work if priming takes more than 15-20 seconds of continuous cranking (with ignition operational).
6. Vapor Lock Persistence: If vapor lock issues persist after pump replacement, it indicates the core problem lies elsewhere: fuel line routing too close to exhaust/intake manifolds, insufficient line shielding, poor tank venting, or simply using modern low-vapor-pressure fuel blends in hot weather. Focus on insulating fuel lines or installing a modern return-style regulator system (a more complex modification).
7. Consistent Pressure: If using a gauge, ensure pressure remains within 2.5-4 PSI consistently at idle and under load (requires driving).

Sourcing Quality Parts and Expert Advice

Choosing reliable suppliers is paramount:

• Reputable Vendors: Stick with established suppliers specializing in early Ford V8 parts. Bratton's Antique Auto Parts, MAC's Antique Auto Parts, C&G Early Ford Parts, Dennis Carpenter Ford Restoration Parts, and Sacramento Vintage Ford have strong reputations for correct, quality reproduction parts and knowledgeable support.
• Emphasize Ethanol Resistance: Verify before purchasing that the diaphragm in a new pump or rebuild kit is explicitly designed for modern ethanol-blended fuels (Nitrile or Viton). Don't assume.
• OEM Part Numbers: Know your OEM number (91A-9350) and ensure reproductions are correct for 1940 and specifically the Flathead V8 block. Some pumps look similar but have different arm profiles for other engines/years.
• Technical Support: Reputable suppliers often have knowledgeable staff who can answer specific questions about pump applications and compatibility.

Beyond the Pump: The Fuel System Ecosystem

The 1940 Ford fuel pump is only one component. For reliable operation, consider the entire system:

• Fuel Tank: Ensure it is clean and free of rust/debris blocking the pickup tube. If rusty, flushing and sealing (KBS Coatings, Red-Kote) or replacement is wise.
• Fuel Lines: Inspect the entire steel line from tank to pump and pump to carburetor. Look for kinks, corrosion, or damage. Replace with correct-diameter steel or copper-nickel line if necessary. Ensure proper routing away from extreme heat sources.
• In-Line Filters: Adding a modern paper or sintered bronze filter before the pump helps protect it and the carburetor from debris dislodged from the tank or lines.
• Carburetor: A malfunctioning carburetor (stuck float, faulty needle/seat, clogged jets) can mimic or cause symptoms identical to pump failure. Ensure the carburetor is rebuilt, adjusted, and compatible with ethanol fuels (needle/seat material critical).
• Tank Venting: The stock vented fuel cap must be clear. A clogged vent creates a vacuum in the tank, restricting fuel flow to the pump. Symptoms include initial running until vacuum builds, then stalling.

Historical Context: The 1940 Ford and its Fuel System

1940 was a landmark year for Ford, featuring distinctive styling cues like the prow-like front end, integrated headlights, and the introduction of the popular "Deluxe" models. While pre-WWII, these were relatively sophisticated machines for their time. The reliability of the mechanical fuel pump was well-proven by then. Understanding this system provides a direct link to experiencing these iconic vehicles as they were designed to operate. Using the correct 1940 Ford fuel pump ensures authenticity and historical accuracy in preservation and restoration efforts.

Summary: Keeping the Heart Pumping

The 1940 Ford fuel pump, a seemingly simple component, plays a mission-critical role. Recognizing failure symptoms early, performing correct diagnostics, choosing a high-quality ethanol-compatible replacement pump or rebuild kit, and executing a careful installation are essential skills for any owner or restorer. Paying close attention to details like the lever arm profile, pressure specification, sediment bowl maintenance, and the use of ethanol-resistant materials guarantees reliable performance, allowing you to enjoy the smooth operation of your 1940 Ford’s Flathead V8 for countless miles. Regular visual inspections and awareness of performance changes remain the best defense against unexpected fuel system issues, preserving both your driving pleasure and the historic integrity of these cherished automobiles.