Riding Mowers & Tractors: Mower deck vibrates

If the mower vibrates when you engage the cutting blades, there might be a problem with the blade drive system. Deck vibration can be caused by an unbalanced blade, worn pulley or mandrel, bad blade belt or debris caught inside a pulley. Loose nuts or bolts on the pulleys, mandrels or blades can also cause vibration. Remove the mower deck and re-tighten all fasteners. Check for wear on pulleys, mandrels and blades. Replace any worn or damaged components.

riding mowers & tractors

These repairs may help solve your riding mowers & tractors problem

Replace the riding mower mandrel assembly

Replace the riding mower mandrel assembly

The mandrel assembly attaches to the deck and spins the blade to cut grass. A blade won't move if the mandrel locks up. A damaged mandrel causes mower deck vibration and uneven cutting. Examine the mandrels regularly and replace any damaged mandrels.

How to replace a mandrel assembly on a riding lawn mower

If the blade shaft on your riding lawn mower vibrates or won't spin the blade, the mandrel might be worn or damaged. This DIY repair guide and vidoe explain how to replace a riding lawn mower mandrel assembly in just 6 steps.

Repair difficulty
Time required
 30 minutes or less
Read more
Replace a riding mower blade

Replace a riding mower blade

A bent mower blade won't cut grass evenly and may cause mower deck vibration. Dull blades leave ragged edges on cut grass. Inspect mower blades regularly and replace a riding mower blade if it's damaged, bent or dull.

January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower blade

If brown, tattered grass tips make your lawn look sick, one or more blades on your riding mower could be dull or bent. This repair guide and video show how to replace a riding mower blade in 30 minutes or less.

Repair difficulty
Time required
 30 minutes or less
Read more
How to replace a cutting blade on a zero-turn riding mower

If your grass looks tattered after mowing with a zero-turn riding, the problem could be a dull or damaged blade. This easy-to-follow repair guide and video explain how to replace a blade on a zero-turn riding lawn mower.

Repair difficulty
Time required
 30 minutes or less
Read more
Replace the riding mower blade belt

Replace the riding mower blade belt

The blade belt spins the blades to cut the grass. A worn or broken drive belt won't spin the cutting blades so your mower won't cut the grass. A worn blade belt can also cause mower deck vibration or uneven cuts. Examine the blade belt regularly and replace it if it's worn or broken.

How to replace the blade belt on a zero-turn riding mower

If the blades won't spin on a zero-turn riding mower, the problem could be a broken blade belt. Replace a broken or worn blade belt on a zero-turn riding lawn mower by following the steps in this DIY repair guide and video.

Repair difficulty
Time required
 30 minutes or less
Read more
How to replace a riding lawn mower blade drive belt

If the blades on your riding lawn mower don’t spin fast enough—or don’t spin at all—the blade drive belt could be worn out or broken. This repair guide and video show how to replace a blade drive belt in less than an hour.

Repair difficulty
Time required
 45 minutes or less
Read more
Replace the riding mower deck idler pulley

Replace the riding mower deck idler pulley

The deck idler pulley tightens the blade belt against the blade pulleys to spin the blades when you shift the blade engagement lever to engage the blades. You might need to replace the riding mower deck idler pulley if the blades don't spin. A worn idler pulley can also cause uneven cuts and mower deck vibration, so check the idler pulley if you notice these symptoms. Replace the deck idler pulley if it's worn or broken.

Symptoms common to all riding mowers & tractors

Choose a symptom to see related riding mower and lawn tractor repairs.

Main causes: dead battery, stale fuel, bad starter solenoid, ignition system problem, bad ignition interlock switch, clogged carburetor
Main causes: punctured tire or inner tube, leaky valve stem, damaged wheel rim
Main causes: damaged tie rods, bent or worn wheel spindle, worn front axle, damaged sector gear assembly
Main causes: faulty battery, bad alternator
Main causes: engine overfilled with oil, leaky head gasket or sump gasket, damaged carburetor seals, cracked fuel pump, broken fuel line
Main causes: damaged cutting blade, worn deck pulley, damaged mandrel pulley, loose fasteners on mower deck components
Main causes: worn or broken ground drive belt, bad seat switch, transaxle freewheel control engaged, transaxle failure, dirty carburetor
Main causes: shift lever needs adjustment, neutral control needs adjustment
Main causes: unlevel mower deck, dull or damaged cutting blades, worn mandrel pulleys, bent mower deck, engine needs tune up
Repair guides common to all riding mowers & tractors

These step-by-step repair guides will help you safely fix what’s broken on your riding mower or lawn tractor.

How to replace a mandrel assembly on a riding lawn mower

Replace the mandrel assembly if the blade shaft vibrates or doesn't spin.

Repair difficulty
Time required
 30 minutes or less
How to replace the air filter on a riding lawn mower

Get your mower running smoothly again by replacing the air filter—it's a quick job you can do yourself, following these steps.

Repair difficulty
Time required
 15 minutes or less
February 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower ignition switch

Get your mower started again by replacing the ignition switch—it's a quick job you can do by following these steps.

Repair difficulty
Time required
 15 minutes or less
Articles and videos common to all riding mowers & tractors

Use the advice and tips in these articles and videos to get the most out of your riding mower or lawn tractor.

December 1, 2017
Wiring schematic symbols explained video
By Sears PartsDirect staff

Learn some of the most common symbols found in a wiring diagram and what they mean.

May 1, 2017
Troubleshooting a riding lawn mower blown fuse video
By Sears PartsDirect staff

Test the ignition switch and wire harnesses to find the short.

March 1, 2016
How to level a riding lawn mower deck for an even cut video
By Sears PartsDirect staff

Mower not cutting the grass evenly? Your mower deck might be the problem.