How to Measure and Replace a Mower Deck Belt

A worn deck belt shows up as a squeal, blades that slow down in thick grass, or an uneven cut. Replacing it is one of the easiest repairs on a riding mower. The hard part is getting the right belt.

Signs your belt needs replacing

• Cracks, glazing (a shiny, hard surface), frayed edges or missing chunks
• Squealing when you engage the blades
• The belt rolls over or jumps off the pulleys
• Blades that bog down even with sharp blades

Step 1: Find the right belt

Use the OEM part number if you can. It's often printed on the back of the old belt, listed in your owner's manual, or available from the manufacturer's parts lookup using your model and serial number. Search that number on our site to find the matching belt.

If the number is worn off, measure:

• Width: measure across the top of the belt. Common sizes are 3/8" (3L), 1/2" (4L or A section) and 21/32" (5L or B section).
• Length: measure the outside length. Run a flexible tape or a piece of string around the outside of the belt, then measure the string. Don't stretch the belt while measuring.
• Type: deck belts on riding mowers are usually reinforced (often with aramid/Kevlar cord) to handle clutch engagement and heat. A plain V-belt of the same size may wear out quickly on a deck.

Step 2: Remove the old belt

1. Park on level ground, set the parking brake, remove the key and disconnect the spark plug wire.
2. Lower the deck to its lowest cutting height to take tension off the belt.
3. Take a photo of the belt routing, or find the routing decal on the deck. You'll need it for the new belt.
4. Remove the belt covers over the spindles.
5. Release the tension: pull the idler arm back (some mowers need a spring puller or breaker bar) and slip the belt off the pulleys.

Step 3: Install the new belt

1. Route the new belt following your photo or the deck decal. Make sure the V side sits in the V grooves and the flat back runs against the flat idlers.
2. Release the idler slowly so the spring tensions the belt.
3. Spin each pulley by hand and check the belt is seated in every groove.
4. Replace the belt covers, reconnect the spark plug wire and test the blades.

While you're in there

Spin each idler pulley. If one wobbles, grinds or feels rough, replace it now; a bad idler will chew up a new belt quickly.

Shop lawn mower belts, OEM-style replacement belts, Kevlar universal belts in 3/8", 1/2" and 5/8" widths, and pulleys.