If you’ve ever wondered, “why does my treadmill slow down and speed up,” you’re not alone. This frustrating issue is a common problem that can interrupt your workout and be a sign something needs attention.
It’s usually caused by a few specific mechanical or electrical faults. The good news is that many causes are simple to diagnose and fix yourself. Let’s look at what might be happening with your machine.
Why Does My Treadmill Slow Down and Speed Up
This inconsistent speed, often called “surgeing,” points to a problem with power delivery or mechanical resistance. The motor isn’t maintaining a constant load. Think of it like your car struggling to maintain speed on a hill—something is making the work harder or the power weaker at moments.
Common Causes of Treadmill Speed Fluctuations
These are the most likely culprits behind your treadmill’s unstable behavior. Identifying the right one is the first step to a solution.
- Dirty or Worn Drive Belt: The belt connecting the motor to the roller can become glazed or loose. This causes it to slip under load, making the walking belt slow down.
- Friction from a Dirty Walking Belt: A belt that hasn’t been lubricated creates drag. The motor strains, may slow, and then speeds up when it catches.
- A Failing Motor: If the motor’s brushes are worn or it’s overheating, it can’t provide consistent power. You might here a buzzing sound or smell something hot.
- Faulty Speed Sensor: Most treadmills have a sensor that tells the console how fast the belt is moving. If it’s dirty or misaligned, it sends wrong data, causing the motor to over-correct.
- Insufficient Power Supply: Plugging your treadmill into an overloaded circuit or a long extension cord can starve it of the consistent voltage it needs.
- Worn or Loose Roller Bushings: The bearings that let the rollers spin smoothly can wear out. This creates uneven resistance that the motor fights against.
Step-by-Step Troubleshooting Guide
Follow these steps in order to safely find the cause of your treadmill’s speed problems. Always unplug the machine before doing any physical inspection.
Step 1: Check the Basic Power Setup
This is the easiest fix. Ensure your treadmill is plugged directly into a dedicated wall outlet. Avoid power strips or extension cords, as they can cause voltage drops. Try a different outlet on another circuit to rule out a wiring problem in your home.
Step 2: Inspect and Clean the Drive Belt
Unplug the treadmill and remove the motor hood. Locate the wide, flat belt around the motor pulley and front roller. Check for:
- Tension: Press down on the belt midpoint. It should deflect about 1/2 inch to 1 inch. Too much slack causes slipping.
- Condition: Look for a shiny, glazed surface or cracks. This indicates wear and reduced grip.
- Cleaning: Wipe the belt and pulleys with a dry cloth to remove any dust or debris that could cause slippage.
Step 3: Lubricate the Walking Belt
A dry belt is a top cause of surging. Check your owner’s manual for the correct lubricant type (usually silicone-based). Perform the “lift test”:
- With the treadmill off, try to lift the walking belt from the center of the deck.
- If you can’t lift it about 2-3 inches, it likely needs lubrication.
- Apply lubricant as per manual instructions, typically under the edges of the belt along it’s length.
- Run the treadmill at a low speed for a few minutes to spread the lubricant evenly.
Step 4: Test the Speed Sensor
This is a small plastic piece near the front or rear roller, often with a magnet. It should be aligned close to the magnet disc on the roller (about a dime’s thickness apart). Gently clean any dust off both the sensor and the magnet disc with a cloth. Make sure it’s securely fastened and hasn’t become bent.
Step 5: Examine the Motor and Brushes
If the problem persists, the motor might be the issue. Visually inspect the motor casing for burn marks or a hot smell. On many motors, you can access and replace the carbon brushes—small blocks that transfer electricity. If they are less than 1/4 inch long, they need replacing. A local repair shop can often do this affordably.
When to Call a Professional Technician
Some problems are best left to experts for safety and warranty reasons. Consider calling a pro if:
- You’ve tried the steps above and the speed is still inconsistent.
- You see sparking, hear loud grinding, or smell burning from the motor.
- The console shows error codes related to speed or motor after you look them up.
- You’re uncomfortable working with electrical components or taking the machine apart.
A certified technician has the tools to properly test motor capacitors, control boards, and other complex parts.
Preventive Maintenance to Avoid Future Problems
Regular care prevents most speed issues. A little upkeep goes a long way in keeping your runs smooth.
- Monthly: Wipe down the belt and deck to remove dust and debris. Vacuum around the motor compartment if possible.
- Every 3-6 Months: Check walking belt alignment and tension. Lubricate the walking belt as needed (more often with heavy use).
- Annually: Have a technician perform a detailed inspection, especially on older models. They can check internal wiring and component wear you might miss.
- Always: Use a dedicated outlet. Let the motor cool down between long workouts. Avoid letting dust and pet hair accumulate around the base.
FAQ: Treadmill Speed and Performance Issues
Q: Why does my treadmill slow down when I step on it?
A: This is almost always due to a slipping drive belt or a belt that needs lubrication. The extra weight of your body increases the load, and the motor struggles if there’s too much friction or not enough grip.
Q: Can a bad outlet cause my treadmill to speed up and slow down?
A: Yes, absolutely. An outlet on a circuit with other appliances, or one with faulty wiring, cannot deliver the constant, high voltage a treadmill motor requires. This leads to power surges and drops.
Q: Why does my treadmill keep changing speed on it’s own?
A> This is typically an electronic issue. A faulty speed sensor sending incorrect data, a problem with the console circuit board, or a malfunctioning motor control board can all cause the system to randomly adjust speed.
Q: Is it safe to use a treadmill that surges?
A: It’s not recommended. The inconsistent speed can cause you to lose balance and fall. It also puts extreme stress on the motor and electronics, potentially leading to a complete failure or a safety hazard like a fire.
Q: How much does it typically cost to fix a treadmill that’s slowing down and speeding up?
A: If it’s just lubrication, the cost is minimal (just the lubricant). Belt tensioning or drive belt replacement might cost $100-$200 in parts and labor. A motor repair or control board replacement can range from $200 to $500+, depending on the model and part availability.
By understanding the common reasons behind the question “why does my treadmill slow down and speed up,” you can take informed action. Start with the simple checks like power and lubrication before moving to more involved diagnostics. Regular maintenance is the key to preventing this annoying problem and ensuring you get a reliable, smooth workout every time.
For detailed maintenance instructions specific to your model, always refer to your owner’s manual or the manufacturer’s website. A great resource for treadmill troubleshooting tips and repair guides can be found at Treadmill Doctor.