1968 Corvette Fuel Pump: The Complete Guide to Replacement, Selection, and Performance

If you own a 1968 Chevrolet Corvette and need to replace the fuel pump, the most important thing to know is that the original factory-correct part number for the mechanical fuel pump is AC 40658 (GM part number 6417377), which was used on all 1968 Corvettes with 327 cubic inch engines and all 1969 Corvettes with 350 cubic inch engines. This pump delivers fuel pressure between 5¼ and 6½ PSI, and it is a mechanical unit driven by the engine's camshaft. Whether you are restoring a numbers-matching car or simply keeping your C3 on the road, selecting the correct fuel pump is critical for reliable performance and proper engine operation.

Understanding the 1968 Corvette Fuel Pump

The 1968 Corvette marked the debut of the C3 generation, and it came with several engine options. The base engine was a 327 cubic inch V8 producing 300 horsepower, while the L79 option offered a 350-horsepower version of the same 327 engine. For the 1968 model year, all small-block Corvettes used the same fuel pump: the AC 40658. This pump was also shared with the 1969 Corvettes equipped with the base 350 cubic inch engine and the L46 350-horsepower engine.

Key specifications for the 1968 Corvette fuel pump include:

  • Part Number: AC 40658 (also listed as GM 6417377)
  • Fuel Pressure: 5¼ to 6½ PSI
  • Type: Mechanical, camshaft-driven
  • Location: Lower front passenger side of the engine
  • Fuel Delivery: Pulls fuel from the rear-mounted tank and sends it to the carburetor

The fuel pump is mounted on the front of the engine block, and it is operated by a push rod that rides on an eccentric lobe of the camshaft. This design is simple and reliable, but it does require proper alignment and installation to function correctly.

Original vs. Replacement Fuel Pumps

When sourcing a fuel pump for your 1968 Corvette, you have several options. Understanding the differences between them will help you make the right choice for your specific needs.

1. Original (NOS) Fuel Pumps: New Old Stock (NOS) pumps are original GM or AC parts that were manufactured decades ago but never used. These are highly sought after by restorers who want to maintain factory correctness. The NOS AC 40658 pump comes with the original gasket and is still available from specialty suppliers. However, because these pumps are 50+ years old, the internal rubber diaphragms may have deteriorated over time, making them less reliable than a new reproduction or rebuilt unit.

2. Rebuilt Original Fuel Pumps: Several suppliers offer professionally rebuilt original fuel pumps. These start with a genuine AC 40658 core that is disassembled, cleaned, inspected, and fitted with new internal components including diaphragms, valves, and seals. Rebuilt pumps are an excellent option for concours-level restorations because they maintain the correct appearance and date codes while providing modern reliability.

3. Reproduction Fuel Pumps: Reproduction pumps are new-manufacture parts designed to match the specifications and appearance of the original AC 40658. These are widely available from Corvette specialty parts suppliers and are generally the most affordable option. High-quality reproduction pumps are engineered for precision and deliver reliable performance.

4. Universal Aftermarket Fuel Pumps: Generic mechanical fuel pumps are available for 1963-1981 Corvettes. These pumps typically flow 80 GPH at 6 PSI and fit both small-block and big-block applications. Many have a rotatable lower body to help with installation alignment. While these work well for daily drivers or modified cars, they do not have the correct appearance for a restoration project.

How to Identify the Correct Fuel Pump

Identifying whether your 1968 Corvette still has its original fuel pump requires checking the stamped numbers on the pump housing. The AC 40658 pump should have the number "40658" stamped on the flange, along with a date code that indicates when the pump was manufactured.

Date codes on AC fuel pumps use a two-letter system:

  • The first letter represents the month (A=January, B=February, C=March, D=April, E=May, F=June, G=July, H=August, I=September, J=October, K=November, L=December)
  • The second letter represents the year (I=1969, J=1970, etc.)

For a 1968 Corvette, a correct original pump would typically have a date code showing a 1968 production date. However, as noted by Corvette restorers, some cars left the factory with pumps dated from early 1969, especially for late-production 1968 models.

Common part numbers you may encounter include:

  • AC 40658: Correct for 1968 327 and 1969 350 Corvettes
  • AC 40524: Used on 1968 Chevrolet passenger cars with 327 engines, occasionally found on Corvettes but not originally cataloged for them
  • AC 40709: A later replacement pump for 1968-1969 small-block Corvettes, with a different valve chamber design

Step-by-Step Fuel Pump Replacement

Replacing the fuel pump on a 1968 Corvette is a manageable DIY project, but it requires attention to detail and proper preparation. Here is a practical guide to getting the job done right.

Tools and materials you will need:

  • New fuel pump (correct for your application)
  • Fuel pump gasket
  • Socket wrench set with extensions
  • Torque wrench
  • Threadlocker (Loctite 242 recommended)
  • Long bolt (for retaining the push rod)
  • Safety glasses and gloves
  • Fire extinguisher (always have one nearby when working with fuel)

Preparation steps:

  1. Relieve fuel system pressure by removing the fuel pump fuse and running the engine until it stalls, or by disconnecting the coil wire and cranking the engine for 10-15 seconds.
  2. Disconnect the negative battery cable to prevent any accidental sparks.
  3. Jack up the passenger side of the car and support it securely on jack stands. Removing the right front wheel provides better access.
  4. Disconnect the lower radiator hose from the water pump outlet and move it aside. This gives you significantly more room to reach the fuel pump mounting bolts.

Removing the old pump:

  1. Clean the area around the fuel pump to prevent debris from falling into the engine.
  2. Disconnect the fuel inlet line from the pump, then the outlet line to the carburetor. Be prepared for some residual fuel to drip out.
  3. Remove the two mounting bolts that secure the fuel pump to the mounting plate on the engine block.
  4. Carefully pull the pump away from the engine. The push rod may fall out of the block at this point, so have a catch pan or rag ready.
  5. Critical step: Before the push rod falls out, insert a long bolt into the hole on the front of the block (below the water pump outlet) to gently hold the push rod in place. Tighten this bolt just enough to contact the rod—do not overtighten or you could damage it.

Installing the new pump:

  1. Rotate the engine to #1 Top Dead Center (TDC). At this position, the camshaft eccentric is at its lowest point, and the fuel pump push rod is fully retracted into the block. This makes installation much easier because there is less spring tension on the pump rocker arm.
  2. Clean the mounting surface on the engine block thoroughly.
  3. Apply a thin layer of sealant to the new gasket and attach it to the pump mounting flange.
  4. Position the new pump so the rocker arm engages properly with the push rod. The rocker arm must sit on top of the push rod, not beside it.
  5. Install the two mounting bolts and tighten them to 15-20 foot-pounds using a torque wrench. Apply threadlocker to the bolts to prevent them from loosening due to engine vibration.
  6. Reconnect the fuel inlet and outlet lines. Use new sealing washers or O-rings to prevent leaks.
  7. Reconnect the lower radiator hose.
  8. Reconnect the negative battery cable.
  9. Reinstall the right front wheel.

Testing your work:

  1. Turn the ignition key to the ON position (without starting the engine) to allow the fuel pump to prime the system.
  2. Check all connections for leaks. A soapy water solution can help identify small leaks—bubbles indicate escaping fuel.
  3. Start the engine and let it idle. Monitor the fuel pressure if you have a gauge, and listen for any unusual noises.
  4. Check for leaks again after the engine has reached operating temperature.

Common Problems and Troubleshooting

Even with a properly installed fuel pump, you may encounter issues. Here are the most common problems and how to diagnose them.

1. Engine cranks but won't start: If the engine turns over but does not fire, the fuel pump may not be delivering fuel. Disconnect the fuel line at the carburetor and crank the engine briefly. If no fuel comes out, the pump may be faulty, the push rod may be worn, or the fuel line from the tank may be blocked.

2. Low fuel pressure: A fuel pressure test should show 5¼ to 6½ PSI at idle. If pressure is low, the pump diaphragm may be failing, or the fuel filter may be clogged. Replace the fuel filter first, as it is the simpler and cheaper fix.

3. Fuel leaks: Leaks typically occur at the gasket between the pump and the engine block, or at the fuel line fittings. Verify that the mounting bolts are torqued correctly and that the gasket is properly seated. For line fittings, use new sealing washers and tighten carefully to avoid stripping the threads.

4. Excessive noise from the pump: A clicking or tapping noise from the fuel pump area usually indicates a worn push rod or a misaligned rocker arm. The pump rocker arm must be correctly positioned on top of the push rod. If the push rod is worn, it will need to be replaced.

5. Fuel in the engine oil: If the pump diaphragm develops a tear, fuel can leak through the pump body and into the engine's crankcase. This will cause the oil level to rise and the oil to smell like gasoline. If you notice this, stop driving immediately and replace the fuel pump. Driving with fuel in the oil can cause serious engine damage.

Performance Upgrades and Modern Alternatives

If you are building a driver-quality 1968 Corvette rather than a show car, you have several options for improving fuel delivery beyond the stock mechanical pump.

High-performance mechanical pumps: Several manufacturers offer mechanical fuel pumps with higher flow rates than the original AC 40658. These pumps typically flow 80-110 GPH and maintain 6-7 PSI of pressure, which is sufficient for most street-driven small-block engines making up to 450 horsepower. They are direct replacements that bolt on without modifications.

Electric fuel pump conversions: For modified engines with higher horsepower demands or aftermarket fuel injection systems, an electric fuel pump is the better choice. The 1968-1974 Corvette can be fitted with an in-tank electric fuel pump module that delivers 255 liters per hour (LPH) at a regulated 58 PSI, supporting up to 550 horsepower. These systems are designed as direct replacements for the factory fuel pickup and sending unit, so no custom fuel tank is required.

Important note: If you convert to an electric fuel pump, you must install a fuel pressure regulator and verify that the system is compatible with your carburetor or EFI setup. Electric pumps are not plug-and-play with stock mechanical pump systems.

Where to Buy a 1968 Corvette Fuel Pump

You can find 1968 Corvette fuel pumps from several sources, each with different advantages:

  • Corvette specialty suppliers: Companies like Corvette Pacifica and RPI Designs offer rebuilt original pumps and high-quality reproductions specifically for 1968-1969 Corvettes. These are the best option for restoration projects.

  • General auto parts stores: Retailers carry universal replacement pumps that fit 1963-1981 Corvettes. These are affordable and readily available but may not have the correct appearance for a show car.

  • Online marketplaces: NOS and used original pumps can be found on auction sites and Corvette forums. Be cautious with NOS pumps—verify the date code and condition before purchasing.

Why Choose KEMSO for Your Fuel Pump Needs

When it comes to selecting a reliable fuel pump for your 1968 Corvette, KEMSO offers a superior solution that combines high performance, OEM-quality replacement, and exceptional value. Every KEMSO fuel pump is engineered to meet or exceed original equipment specifications, ensuring that your Corvette runs smoothly and reliably for years to come.

KEMSO fuel pumps are designed for:

  • High performance: Built to deliver consistent fuel flow and pressure under all driving conditions
  • OEM replacement: Precision-fit design that matches the original specifications of your vehicle
  • Durability: Constructed from high-quality materials that withstand the demands of both daily driving and performance applications

What sets KEMSO apart is their lifetime warranty. When you purchase a KEMSO fuel pump, you are backed by a promise of confidence that protects your investment. This commitment to quality means you can install your pump and drive with peace of mind, knowing that KEMSO stands behind their product.

Visit https://www.kemsoracing.com/ to browse their selection of high-performance fuel pumps and find the perfect fit for your 1968 Corvette. Whether you need a direct OEM replacement or a performance upgrade, KEMSO has the solution you need.

Final Thoughts

The 1968 Corvette fuel pump is a critical component that directly affects your car's performance and reliability. Whether you choose an original AC 40658 for a concours restoration, a reproduction pump for a driver, or a modern electric conversion for a modified car, proper installation and maintenance are essential. Always verify that the pump you select matches your engine's specifications, and take the time to install it correctly.

For the best combination of performance, reliability, and value, consider KEMSO fuel pumps. Their commitment to OEM-quality replacement parts and lifetime warranty makes them a trusted choice for Corvette owners who demand the best. Visit https://www.kemsoracing.com/ today to find the right fuel pump for your 1968 Corvette and keep your classic on the road for years to come.


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