🔧 MX-5 Miata - Serpentine Belt Replacement

The serpentine belt (also called the accessory drive belt) spins key accessories like the alternator and A/C. Replacing it is important if it’s cracked, squealing, or slipping, because a failed belt can leave you stranded.

Difficulty Level: Intermediate | Estimated Time: 0.5-1.0 hours

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⚠️ Safety & Precautions

• 🧤 Work on a cool engine; belts and pulleys can burn you.
• 🔒 Keep fingers/tools clear of pulleys; never crank the engine during the job.
• 👓 Wear safety glasses; debris can fall while working near the front of the engine.
• 🔋 Battery disconnect is not required, but keep the key far away so the car can’t be started accidentally.

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🔧 Required Tools

You'll need the following tools for this repair:

• 14mm socket
• 3/8" drive ratchet
• 3/8" drive breaker bar (18"-24")
• 3/8" drive extension set (3", 6")
• Trim clip removal tool
• Flathead screwdriver
• Work light
• Nitrile gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Accessory drive belt (serpentine belt) - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Open the hood and use a work light to locate the belt routing sticker/diagram (often on the radiator support). If there’s no sticker, take a clear photo of the current belt routing before removing it.
• Inspect the belt area for oil/coolant leaks. Fix leaks first, or the new belt may fail early.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Create working room at the front of the engine

• Use a flathead screwdriver and trim clip removal tool to loosen/remove any plastic clips holding the front intake snorkel/ducting (if equipped).
• Use a 10mm socket with a 3/8" drive ratchet (or the correct fastener tool you see) to loosen the intake duct/airbox fasteners enough to move the ducting aside for access.
• Tip: Don’t fully remove parts unless needed.

Step 2: Locate the belt tensioner

• Find the spring-loaded belt tensioner at the front of the engine (it has an arm and a pulley pressing on the belt).
• Fit a 14mm socket on the tensioner’s hex boss/bolt head using a 3/8" drive ratchet or 3/8" drive breaker bar (18"-24").
• A breaker bar is a longer handle that makes it easier to rotate tight parts safely.

Step 3: Release tension and remove the old belt

• Use the 3/8" drive breaker bar (18"-24") to rotate the tensioner smoothly (you’ll feel the spring load).
• While holding the tensioner rotated, use your other hand to slip the belt off the easiest top pulley (commonly the alternator pulley).
• Slowly let the tensioner return to its resting position. Do not let it snap back.
• Remove the belt from the remaining pulleys and lift it out.

Step 4: Compare belts and check pulleys

• Lay the old and new belt side-by-side to confirm the new belt matches in length and rib count.
• Spin each accessible pulley by hand and listen/feel for grinding or wobble.
• Check the tensioner pulley surface for cracks or roughness.

Step 5: Install the new belt (route first, then tension last)

• Route the new belt around all pulleys following the routing diagram/photo, leaving one easy-to-reach pulley for last.
• Make sure all ribs are seated in the pulley grooves (no ribs hanging off the edge).
• Use the 14mm socket and 3/8" drive breaker bar (18"-24") to rotate the tensioner again.
• Slip the belt over the final pulley, then slowly release the tensioner.

Step 6: Reinstall any intake ducting you moved

• Reposition the ducting and secure it using the same fasteners with a 10mm socket and 3/8" drive ratchet, plus any clips using a trim clip removal tool.
• Confirm nothing is touching the belt path.
• Tip: Double-check belt alignment one last time.

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✅ After Repair

• Start the engine and watch the belt for 15–30 seconds. It should run centered and smooth with no wandering.
• Listen for chirping/squealing. If you hear noise, shut it off and re-check that the belt ribs are seated correctly on every pulley.
• Take a short test drive and re-check for noise afterward.

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💰 DIY vs Shop Cost

Shop Cost: $150-$300 (parts + labor)

DIY Cost: $25-$70 (parts only)

You Save: $125-$230 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.5-1.0 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.