John Deere S100 Problems | Riding Mower Repair Guide

The John Deere S100 series (S100, S120, S130, S140) are entry-level riding tractors designed for residential lawns. While they carry the John Deere name, they’re built to a price point and develop predictable issues. This guide covers common problems and practical solutions.

Table of Contents

• S100 Series Overview
• Engine Problems
• Transmission Issues
• Deck and Cutting Problems
• Electrical Issues
• Maintenance Schedule

S100 Series Overview

Model	Engine	Cut Width	Trans Type
S100	17.5HP Briggs	42”	CVT
S120	22HP Briggs V-Twin	42”	CVT
S130	22HP Briggs V-Twin	42”	CVT
S140	22HP Briggs V-Twin	48”	CVT

[NEED REAL IMAGE: John Deere S100 series model badge and engine]

Key Features:

• Continuous variable transmission (CVT)
• Electric PTO for blade engagement
• Automatic choke on most models
• Made by MTD under John Deere license

Engine Problems

Won’t Start - Cranks But No Fire

Safety system check first: John Deere uses multiple safety switches. Engine won’t start unless:

• Operator in seat
• Brake pedal depressed
• PTO disengaged
• Transmission in neutral

If safety system checks pass:

1. Fuel issues - Most common cause

   • Check fuel level
   • Inspect fuel for water/contamination
   • Verify fuel shutoff is ON
   • Check fuel filter

2. Spark plug - Remove and inspect

   • Should have tan color
   • Replace if fouled or worn

3. Carburetor - Likely gummed up

   • Clean or replace (see carburetor guides)
   • Anti-afterfire solenoid may have failed

Engine Runs Rough or Surges

Common causes:

1. Dirty air filter - Check and replace
2. Carburetor issues - Clean jets
3. Governor linkage - Check for binding
4. Old fuel - Replace with fresh gas

V-Twin specific (S120/S130/S140):

• Check both spark plugs
• Verify both cylinders firing
• Inspect valve clearances if high hours

Engine Overheats

Symptoms: Engine shuts down, hot to touch, temperature warning light.

Check:

1. Cooling fins - Remove grass and debris
2. Engine shroud - Must be in place
3. Oil level - Low oil causes overheating
4. Ground speed - Mowing too slowly overloads engine

Engine Backfires on Shutdown

Cause: Anti-afterfire solenoid failed.

Fix: Replace solenoid ($20-35). Located on carburetor bowl. See carburetor section for details.

White/Blue Smoke

On startup only: Normal oil burning after storage

Continuous smoke:

• Check oil level (overfilled?)
• Verify correct oil type (SAE 30 or 10W-30)
• May indicate ring or seal wear on high-hour engines

Transmission Issues

The S100 series uses a CVT (Continuous Variable Transmission) - a belt-driven system, not a true hydrostatic.

Mower Won’t Move

Check in order:

1. Parking brake - Must be released
2. Drive belt - Inspect for breakage or slipping off
3. CVT belt - May need replacement
4. Transmission engagement - Verify linkage connected

[NEED REAL IMAGE: John Deere S100 drive belt routing]

Loss of Speed or Power

Symptoms: Mower struggles on hills or moves slowly.

Causes:

1. Worn drive belt - Slipping reduces power
2. Belt tension - Spring may be weak
3. CVT wear - Belt and pulley wear over time
4. Transmission oil - Some models have serviceable trans

Belt replacement: The CVT belt is a wear item. Replace every 100-150 hours or when symptoms appear. Use genuine John Deere belt for best results.

Jerky Movement

Symptoms: Mower lurches or doesn’t accelerate smoothly.

Check:

1. Belt condition - Cracked or glazed?
2. Pulley condition - Grooves worn?
3. Linkage adjustment - Speed control cable
4. CVT dust - Clean debris from drive area

Strange Noises From Transmission

Squealing:

• Belt slipping
• Pulley bearing failing

Grinding:

• Belt riding on pulley edge
• Internal CVT damage

Clicking:

• Debris in drive system
• Broken linkage

Deck and Cutting Problems

Uneven Cut

Symptoms: Ridges, scalping, missed strips.

Systematic check:

1. Tire pressure - Equal pressure side to side
2. Deck level - Front 1/8”-1/4” lower than rear
3. Blade condition - Sharp, balanced, not bent
4. Deck shell - Check for damage

Deck leveling procedure:

1. Park on flat surface
2. Measure blade tip height at all four corners
3. Adjust deck hanger rods as needed
4. Verify with measurement

Blades Won’t Engage

Symptoms: Push PTO switch but blades don’t spin.

Check:

1. PTO switch - May have failed
2. PTO clutch - Electric clutch under deck
3. Deck belt - May be broken
4. Safety switches - Operator presence required

Testing PTO clutch: With engine off, you should hear a click from clutch when PTO is switched. No click = electrical issue or failed clutch.

Excessive Vibration

Symptoms: Mower shakes when blades engaged.

Causes:

1. Bent blade - Replace immediately
2. Unbalanced blade - Balance after sharpening
3. Loose blade - Retorque to spec
4. Spindle bearing - Worn bearing causes wobble
5. Deck damage - Check for cracks

Poor Cut Quality

Solutions:

1. Sharpen blades - Should be sharp enough to cut paper
2. Slow down - Let deck clear grass
3. Proper height - Never remove more than 1/3 of blade
4. Clean deck - Remove buildup underneath
5. Overlap passes - Don’t leave strips

Electrical Issues

Battery Won’t Hold Charge

Common causes:

1. Old battery - 3-5 year lifespan typical
2. Charging system - Stator or regulator failed
3. Parasitic draw - Something draining battery
4. Loose connections - Check terminals

Testing charging system:

1. Fully charge battery
2. Start mower, run at full throttle
3. Measure voltage at battery (should be 13.5-14.5V)
4. Below 13V = charging system problem

Starter Clicks But Doesn’t Crank

Causes:

1. Weak battery - Needs charge or replacement
2. Starter solenoid - May be failing
3. Starter motor - Worn brushes or bad connection
4. Ground connection - Check for corrosion

No Electrical Power at All

Check:

1. Main fuse - Usually under hood or near battery
2. Battery connections - Tight and clean?
3. Ignition switch - May have failed
4. Ground strap - Battery to frame connection

Safety Switches Causing Problems

Symptoms: Random shutoffs, won’t start intermittently.

Common culprits:

1. Seat switch - Most common failure
2. Brake switch - Second most common
3. PTO switch - Wears over time

Diagnosing: Unplug suspect switch and jumper connector (temporarily). If problem solves, replace that switch. Never leave safety switches bypassed.

Maintenance Schedule

Every 25 Hours

• Check oil level
• Inspect air filter
• Check tire pressure
• Clean debris from engine area

Every 50 Hours

• Change oil
• Clean air filter or replace
• Sharpen blades
• Lubricate pivot points

Every 100 Hours

• Replace air filter
• Replace spark plug(s)
• Replace fuel filter
• Check belt condition
• Inspect all safety switches

Annually

• Full belt inspection/replacement
• Battery load test
• Complete cleaning and inspection
• Professional deck leveling

Common Parts

Part	Part Number	Cost
Air filter	GY20575	$15-25
Oil filter	AM125424	$8-12
Spark plug	RC12YC	$4-6
Drive belt	GX20072	$25-40
Blade (42”)	GX22151	$25-35
Battery	TY25878	$60-80

Frequently Asked Questions

Are S100 series mowers reliable?

They’re entry-level machines built to a price. Expect 7-10 years with proper maintenance. More issues than higher-end John Deere models.

Can I use aftermarket parts?

Yes for many items. Use genuine for belts and blades. Aftermarket filters and spark plugs work fine.

Why does John Deere use Briggs engines?

S100 series are manufactured by MTD under license. Briggs engines are standard for this class. Higher-end Deere tractors use Kawasaki.

Is the S100 worth repairing vs replacing?

Depends on age and condition. If engine and transmission are sound, most repairs are worthwhile. Major engine or CVT failure on older units may not be economical.

---

The S100 series offers the John Deere name at an accessible price. Keep up with maintenance, address issues early and these tractors provide years of reliable mowing.