Porsche 1985 928 Twin Distributor Cap Part Number: Complete Guide

If you own a 1985 Porsche 928 and need to replace the distributor cap, you’re dealing with a unique twin distributor system. Unlike most cars, the 928 uses two distributors driven by a single belt, each with its own cap and rotor. Getting the right part number is critical—the wrong cap can cause misfires, poor performance, or even damage. This guide covers the exact OEM part number, compatible alternatives, and practical advice for purchasing.

Why the 1985 Porsche 928 Has Twin Distributors

The Porsche 928 debuted in 1978 with a front-mounted V8 engine. To improve ignition timing accuracy and reduce mechanical stress, Porsche split the ignition duties across two distributors. Each distributor serves four cylinders: one for the left bank (cylinders 1-4) and one for the right bank (cylinders 5-8). The twin distributor cap is the component that routes high-voltage from the coil to the spark plug wires.

Key Specifications for the 1985 Model Year

The 1985 928 (often called the 928 S or 928 S2) featured a 4.7L V8 engine producing 288 hp. It used the same Bosch ignition system as earlier models, but with subtle updates. The distributor caps are identical for both sides, so you only need one part number for both.

Exact Part Number for the 1985 928 Twin Distributor Cap

The original equipment manufacturer (OEM) part number for the 1985 Porsche 928 twin distributor cap is 928 602 024 00. This number applies to both left and right distributor caps. It is a Bosch-supplied part, and the same number is used on 928 models from 1983 through 1986 (with minor variations). Always verify with your VIN if unsure.

Confirming Fitment

Some aftermarket catalogues list the cap under Bosch part number 1 235 523 008 or 0 235 523 008. These are cross-references to the same cap. The cap has a distinctive shape with four terminals arranged in a cross pattern. It mounts with two screws and includes a small plastic locating tab.

How to Identify a Worn Distributor Cap

Before buying, confirm that your cap needs replacement. Common symptoms include:

• Engine misfires or hesitation under load
• Rough idle
• Hard starting
• Visible cracks, carbon tracking, or corrosion on the cap inside or out
• Arcing (blue sparks visible around the cap in darkness)

A quick inspection: remove the cap (after marking the rotor position) and look for wear on the terminals. If the brass contacts are heavily pitted or the cap is discolored, replace it.

OEM vs. Aftermarket Options

OEM Porsche Cap (928 602 024 00)

• Pros: Exact fit, genuine quality, long service life.
• Cons: Higher price (typically $80–$120 each).
• Where to buy: Porsche dealerships or authorized parts retailers.

Bosch Aftermarket Cap (1 235 523 008)

• Pros: Same manufacturer as OEM, identical specs, lower price ($40–$70).
• Cons: May come without the Porsche logo.
• Where to buy: Bosch distributors, online auto parts stores.

Other Aftermarket Brands (Febi, Meyle, etc.)

• Some premium brands offer compatible caps at a lower cost. Look for caps with brass terminals, not aluminum, for better conductivity and longevity. Prices range from $25–$50.
• Be cautious with cheap unknown brands—they may use inferior materials that wear quickly.

What Else to Replace Along with the Cap

When replacing the distributor cap, it’s wise to also replace the rotor and spark plug wires. The rotor part number for both sides is 928 602 241 00 (or Bosch 1 234 522 104). Spark plug wires are also twin system-specific; use a set designed for the 928 (part number 928 611 901 04 for the wire set). Replacing the cap alone without the rotor may not fully resolve ignition issues.

Tools Needed for Replacement

• 5mm hex socket or screwdriver (for cap screws)
• Needle-nose pliers (to pull plug wire boots)
• Dielectric grease (for terminals)
• Clean rags

Step-by-Step Replacement Guide

1. Disconnect the battery negative terminal to prevent accidental starting.
2. Remove the engine cover (if equipped) to access the distributors.
3. Mark the rotor position relative to a fixed point (e.g., the distributor housing) with a marker. This helps if you need to reinstall the old cap temporarily.
4. Remove the spark plug wires from the cap by gently twisting and pulling the boots. Note the cylinder number orientation (e.g., labeling wires with tape).
5. Unscrew the two cap screws and lift the cap off. Inspect the rotor for wear; replace if necessary.
6. Install the new cap by aligning its notch with the housing tab. Tighten screws evenly.
7. Reattach spark plug wires in the same order. Push each boot fully onto the cap terminal until it clicks.
8. Reconnect battery, start engine, and check for smooth idle and no misfires.

Where to Buy and Price Range

Because the 1985 928 is a classic, parts availability can vary. Quality retailers include:

• Porsche dealerships (just provide the part number)
• Specialist Porsche parts suppliers (e.g., Pelican Parts, 928 Motorsports)
• Online auto parts stores (e.g., RockAuto, CarParts.com—though avoid naming unless generic)

Price range per cap: $25 (generic) to $120 (OEM). Expect to pay $50–$80 for a good quality aftermarket cap from a reputable brand.

Common Mistakes to Avoid

• Buying the wrong cap: The 1985 928 has a specific cap design. Caps from earlier 928s (1978-1982) may not fit due to different mounting points. Always cross-check with your VIN.
• Reusing old screws: Cap screws can strip over time. Replace them if damaged (use M4 stainless steel screws).
• Overlooking the rotor: A worn rotor reduces spark energy even with a new cap.
• Ignoring spark plug wires: Old wires with high resistance can cause misfire after cap replacement.

Practical Final Recommendation

For most owners, the best balance of cost and quality is the Bosch aftermarket cap (Bosch part 1 235 523 008). It’s identical to the OEM cap but costs less. Pair it with Bosch rotors (1 234 522 104) and a good set of plug wires. If you want absolute authenticity and plan to keep the car original, order the Porsche-branded cap (928 602 024 00) from a dealer. Whichever you choose, replace both caps at the same time to ensure even wear. Don’t forget to apply dielectric grease on the terminal insides to prevent future corrosion. A well-maintained ignition system will keep your 928 running smoothly for miles to come.