Distributor Cap Guide for the 1958-1959 GMC F350 Truck
Keep your classic GMC running strong by learning how to spot a bad distributor cap and choose the right replacement.
- A bad distributor cap causes misfires, rough idle, and hard starting.
- Always replace the distributor rotor at the same time as the cap for a complete repair.
- Choose a cap with brass terminals for better durability and conductivity.
- Ensure you order the correct part for your engine (V8 or 6-cylinder).
Signs of a Failing Distributor Cap
A distributor cap is a part that wears out over time from heat and the constant passage of high voltage. When it starts to fail, your truck's performance will suffer. A bad cap can't deliver a consistent spark, leading to several noticeable problems.
Common symptoms include engine misfires (which feel like a stumble or jerk), a rough idle, trouble starting the engine, and sometimes even backfiring. You might also notice the engine feels sluggish or shakes when you accelerate. A visual inspection can often confirm the problem. Look for cracks in the plastic, corrosion on the metal terminals, or thin black lines that look like pencil marks, which are called carbon tracks. Any of these signs mean it's time for a replacement.
Choosing the Right Aftermarket Part
Original GM parts for a 1958 or 1959 truck are no longer made. Your options are new aftermarket parts or "New Old Stock" (NOS), which are original parts that were never sold. NOS parts can be very expensive and their materials may have degraded over time. For these reasons, a quality new aftermarket part is usually the most reliable and affordable choice.
| Brand Tier | Description |
|---|---|
| Premium Aftermarket (e.g., Standard Ignition) | Standard Motor Products (SMP) is a well-respected brand for ignition components on classic American vehicles. Their caps are often made with high-quality materials like high dielectric-strength polymers and sometimes feature brass terminals, which offer better conductivity and corrosion resistance than standard aluminum. This is a solid choice for reliability and longevity. |
| Standard Aftermarket (e.g., Walker Products) | Walker Products provides quality replacement parts that are designed to meet or exceed original specifications. These caps are a great balance of affordability and performance, built to restore original function and fix common issues like misfires and hard starts. They are a dependable option for a standard tune-up. |
Pro Tip: When you replace the distributor cap, you should always replace the distributor rotor at the same time. The rotor is an inexpensive part that experiences the same wear and tear as the cap. Also, carefully label your spark plug wires before removing the old cap to ensure they go back on the new one in the correct firing order.
Frequently Asked Questions
What's the difference between aluminum and brass terminals?
Distributor caps come with either aluminum or brass terminals. Brass is a better conductor of electricity and resists corrosion better than aluminum. While caps with aluminum terminals are often cheaper, a cap with brass terminals will typically last longer and provide a more consistent spark.
How do I know if I need a cap for a 6-cylinder or V8 engine?
The cap must match your engine. A 6-cylinder engine uses a cap with 7 towers (one for the coil, six for the plugs), while a V8 engine uses a cap with 9 towers (one for the coil, eight for the plugs). Your 1958-1959 GMC could have come with a 270 cubic inch inline-6 or a 336 cubic inch V8, so be sure to order the correct part for your specific engine.
Are there any recalls for the distributor cap on a 1958-1959 GMC truck?
No. Searches of the National Highway Traffic Safety Administration (NHTSA) database show no recalls specifically for the distributor cap on these vehicles. The NHTSA was formed after these trucks were built, and their database generally does not include recalls older than 15 years unless a manufacturer provides extended coverage.
Can I replace the distributor cap myself?
Yes, this is a very straightforward job for a DIY mechanic. It typically only requires basic hand tools. The process involves removing the spark plug wires (keeping them in order), unscrewing or unclipping the old cap, swapping the rotor, and installing the new cap. Just be sure to put the spark plug wires back in the correct firing order.
Technical Specifications
Vehicle uses a points-style distributor. Cap must match engine type (GMC 270 I6 or 336 V8). Aftermarket caps are available with either aluminum or brass terminals.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.