Ignition Contact Set Guide for the 1939-1940 GMC AC100
Keep your classic GMC's ignition system reliable by understanding and maintaining its ignition points.
- The ignition contact set (points) is a critical wear item that needs regular inspection and replacement.
- Symptoms of failure include rough running, stalling, difficulty starting, and reduced power.
- Always replace the condenser at the same time as the points to ensure longevity.
- Standard Ignition is a trusted aftermarket brand for these components.
Symptoms of a Failing Ignition Contact Set
Ignition points are a wear item and require regular service. As the rubbing block wears down or the contacts become pitted and burned, you will notice performance issues. Recognizing these signs early can prevent a breakdown.
🎬 Watch this guide on classic car symptoms you shouldn't ignore.- Engine Misfires or Runs Rough: This is a very common symptom of failing points. Worn or dirty contacts create an inconsistent spark, causing the engine to run unevenly, shake, or hesitate during acceleration.
- Difficulty Starting or No-Start: If the points are badly worn, pitted, or misaligned, they can't deliver the strong, timely spark needed to start the engine. You might find the engine cranks but refuses to fire up.
- Engine Stalling: Worn points can cause the engine to stall, especially at idle or when coming to a stop. This happens because the spark becomes too weak or inconsistent at low RPMs.
- Reduced Power: A weak or intermittent spark from failing points leads to inefficient combustion. This wastes fuel and reduces the engine's power, making the truck feel sluggish.
Choosing the Right Aftermarket Ignition Contact Set
For a vintage truck like the 1939-1940 GMC AC100, new original equipment (OEM) parts are no longer manufactured. All new replacement ignition contact sets are from aftermarket brands. The key is to choose a quality part that is known for reliability.
Brand Spotlight: Standard Ignition
Standard Ignition, particularly their 'Blue Streak' line, is a well-regarded brand for classic vehicle ignition components. They are known for making quality parts that meet or exceed original specifications. Forum discussions among classic car and tractor owners often recommend Standard Ignition points as a reliable choice. Given the limited availability of parts for this vehicle, Standard Ignition is a trusted option.
Cost of Replacing an Ignition Contact Set
| Part Type | Price Range |
|---|---|
| New Aftermarket (Standard Ignition) | $21.44 |
| Shop Labor | $100 - $200 |
Prices are estimates and may vary based on location and supplier.
A Note on the Condenser
The condenser is a small capacitor that works with the points. Its job is to prevent a large arc from forming across the points as they open, which protects them from burning out prematurely. It is highly recommended to replace the condenser at the same time as the ignition contact set. A failing condenser will cause the new points to wear out very quickly.
Frequently Asked Questions (FAQ)
What is the difference between ignition points and electronic ignition?
Ignition points are a mechanical switch system used in older vehicles like the 1939-1940 GMC AC100. Electronic ignition, found in modern cars, uses sensors (like magnetic or optical sensors) to do the same job without mechanical contacts. Electronic systems do not have parts that wear out like points do, and they offer more precise spark timing.
How often should I replace the ignition contact set?
Ignition points are a regular maintenance item. They typically need to be replaced every 6,000 to 12,000 miles, or as part of an annual tune-up. Regular inspection for pitting, burning, or wear on the rubbing block is a good practice.
What does it mean to "gap" the points?
Gapping the points refers to setting the correct maximum distance between the contacts when they are opened by the distributor cam. This gap is critical. If it's too small, the coil can overheat; if it's too large, the spark will be weak. The gap is set using a feeler gauge and is a crucial step during installation.
🎬 See how to replace and adjust your ignition points properly.Are there any recalls for the ignition system on a 1939-1940 GMC AC100?
No, there are no official recalls or Technical Service Bulletins (TSBs) from agencies like the NHTSA for this vehicle due to its age. All maintenance and repairs are based on standard automotive practices from the era.
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Technical Specifications
The most critical specification is the point gap, which must be set with a feeler gauge during installation. This measurement ensures the correct dwell angle for proper coil saturation and spark timing.
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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.