ATP Parts ZA-578 Clutch Flywheel Ring Gear

Clutch Flywheel Ring Gear for Ford Applications

ATP Parts ZA-578 is a clutch flywheel ring gear built for Ford applications that use a 138-tooth ring gear with the listed dimensions. It engages the starter motor during cranking, so worn or broken teeth can prevent reliable engine start-up.

Key Features

• Part number: ZA-578
• 138-tooth ring gear for starter engagement
• Inside diameter: 10.475 in.
• Outside diameter: 11.642 in.
• Thickness: 0.373 in.
• Ring gear chamfer: none
• OE-style fit and function for direct replacement use

Detailed Description

This ATP Parts clutch flywheel ring gear is engineered to match the original part’s fit and operating profile for Ford Ranger, Ford Explorer, Ford Bronco II, Ford Aerostar, Ford Mustang, Ford Pinto, and Mercury Capri or Bobcat applications listed below. The ZA-578 ring gear uses 138 teeth and the specified 10.475-inch inside diameter, 11.642-inch outside diameter, and 0.373-inch thickness to support proper starter engagement and dependable engine cranking. This part cross-references AMS Automotive 4736 for the same application.

Vehicle Fitment

• Fits 1991-2000 Ford Explorer, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1983-2000 Ford Ranger, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1986-1990 Ford Bronco II, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1986 Ford Aerostar, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1979 Ford Mustang, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1975-1979 Ford Pinto, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1975-1979 Mercury Bobcat, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1979 Mercury Capri, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"
• Fits 1974-1977 Mercury Capri, N/A — Width: 0.373"; Teeth: 139; Outer Diameter: 11.642"; Inner Diameter: 10.475"

What It Helps Address

• Starter motor engagement problems caused by worn ring gear teeth
• Cranking issues related to broken or damaged flywheel teeth
• Intermittent no-start conditions tied to ring gear wear
• Noise during starter engagement from damaged tooth profiles
• Flywheel service needs on Ford Ranger and Ford Explorer applications

Installation Notes and Tips

Verify tooth count, inside diameter, outside diameter, and thickness before installation. Confirm the flywheel or clutch assembly matches the listed application details for your Ford or Mercury vehicle. Proper alignment during installation is important so the starter gear engages cleanly across the full tooth profile.

Quality Assurance

ATP Parts designs this ring gear to fit and function like the original component, with dimensions and tooth profile selected for durability and long service life in the listed applications. Part number ZA-578 is built as a direct replacement ring gear for routine drivetrain repair.