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How to Service a Gravely Zero Turn Lawn Mower: Step-By-Step

You invested a good amount of money into a good-performing zero-turn when you purchased a Gravely zero-turn. Don’t skip performing routine service on your mower and jeopardize that investment.

Performing routine maintenance on your Gravely can prevent costly repair expenses by identifying small problems before they develop into large ones.

Follow the safety guidelines found in your Gravely operator’s manual to ensure safety while working on your mower.

Service a Gravely Zero Turn

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Steps to Service Your Gravely Zero Turn Lawn Mower

Step 1: Gather Your Tools & Supplies


  • Socket or spanner wrenches
  • Filter wrench
  • Deck scraper and/or wire brush
  • Plastic funnel
  • Oil drain pan


  • Engine oil
  • Engine oil filter
  • Hydraulic oil & filters (if required)
  • Spark plugs
  • Air filter
  • Fuel filter
  • Grease
  • Rubber gloves and heavy work gloves
  • Rags or paper towel
  • Mower blades if not sharpening and reusing current blades
  • Fuel stabilizer
  • Cardboard or newspaper to cover the work surface

Step 2: Check Safety Devices and Safety Interlock System

Your Gravely zero turn is equipped with a safety system to minimize injury when operating your mower. This safety interlock system won’t allow the mower deck to run when it doesn’t sense the operator in the seat in addition to several other safety features.

Reference your operator’s manual for a list of these safety features. Make sure they are in working order on your mower. Never operate your Gravely when all these safety elements are not functioning correctly. Doing so can put you at risk of injury.

Inspect the ROPS bar and seatbelt to make sure they are in good condition and functioning correctly.

Step 3: Prepare Your Zero Turn for Maintenance

Park your Gravely on a flat-level surface. Allow it to run for a few minutes to warm the engine oil. Warm engine oil flows better than cold oil. Place cardboard or newspaper under your mower to prevent oil from dripping onto the ground surface.

Before you begin working on your mower, it is important to take a few steps to ensure your Gravely doesn’t move or start while you are working on it.

  • Set your parking brake.
  • Shut off your mower and remove the ignition key.
  • Disconnect the spark plug wires.
  • Take caution working around the hot engine, hot transmission, and sharp mower blades
  • Check your owner’s manual for additional safety tips

Step 4: Change the Engine Oil

Place your oil drain pan under the engine oil drain plug or drain hose, depending on the type your mower uses. Use a rag to clean around the oil fill area and the drain plug to prevent debris from entering the crankcase. Now proceed with the following steps to change your engine oil:

  • Remove your drain plug and allow the oil to run into the drain pan. You can locate your drain plug or hose under the hood and on the side of the engine near the bottom of the engine.
  • Remove the dipstick from the oil fill to allow the oil to flow faster.
  • Once the oil has completely drained, reinstall the drain plug.
  • Remove your engine oil filter. Use a filter wrench to help loosen the filter. Make sure you are prepared to catch the oil that will come out of the used filter.
  • Place a light film of fresh oil on the seal of your new replacement oil filter and install it on your Gravely.
  • Add new oil to your crankcase until it is at the manufacturer’s required oil level. Use the dipstick to verify you have the right amount of oil. You want the oil to be at the full level on your dipstick. Running your mower with a lower or higher oil level can cause engine damage and running problems. It is important to get this step right.
  • Wipe any oil that may have dripped onto your Gravely mower. Place your used oil in a container for recycling. I like to reuse my engine oil bottles and mark them “For Recycling” so I don’t mix them up with new bottles of oil. Make sure you find a recycling center to dispose of used oil. Some auto supply retail stores will accept oil for recycling.

Step 5: Replace the Spark Plug

Remove your spark plug(s) using a 3/4” or 5/8” socket depending on your engine model. Replace with a new spark plug(s).

These should be replaced annually during your Gravely service so you don’t encounter starting or running problems during the season from running bad spark plugs.

Make sure your spark plugs are gapped to the engine manufacturer’s recommendation. Do not reattach your spark plug wires while you are still performing maintenance on your mower. You will reattach them once your service is complete.

If you don’t change your spark plug, you must inspect them and clean them if necessary using a wire brush. Check for broken porcelain or burnt electrode that will require replacement.

Step 6: Replace Your Air Filter

You should replace your air filter at least once a year and more often when operating in dry dusty conditions. Remove the air filter from the air filter housing.

Wipe any dirt that remains in the housing with a dry cloth to remove it. Do not allow any dirt to fall into the air intake. Install a new air filter into the housing and replace the housing cover.

While your air filter should be changed annually, you must regularly check and clean your filter during the mowing season. Check out my article on air filters to find cleaning instructions.

Step 7: Remove Dirt & Debris around Your Cooling Fins and Engine

The area around your engine must be kept cool. When debris collects in your cooling fins and around your engine, air can’t circulate around your engine block and cylinder to keep it cool.

Remove your engine cover and clean the debris around your engine and cover. Remove the debris collecting around your engine cooling fins.

Step 8: Remove Dirt & Debris from Your Hydro Fans and Transmission Area

The hydro fans keep your transmission cool. Clean the debris and dirt from your fans and the transmission area. Be careful when working around your transmissions as they may be hot.

Step 9: Change Your Hydraulic Oil and Filters if Necessary

Operating your Gravely zero turn with low or old transmission fluid can cause your mower to seem weak when moving. It can also cause extensive damage to the transmission.

Most Gravely zero turns must have the transmission oil changed every 400 hours with an initial “break-in period” oil change completed at 75 hours.

Refer to the operator’s manual for the oil change interval required for your model. If you don’t require a full transmission oil and filter change at this time, check your oil level and top off with transmission fuel if needed.

You need the oil level to reach the “full cold” line on the expansion reservoirs. These are located on the top of your mower behind the seat. You will find one for the left transmission and one for the right transmission.

Here are the most common directions for changing the transmission oil on a Gravely zero turn:

  • Park Zero Turn on Flat Surface: Remove the key and engage the parking brake. Wait for all moving parts to stop before working on your zero-turn. Note the engine and transmission can be hot. Take caution when working. 
  • Locate Filters & Remove Guards: You will find a filter located near each rear wheel. There may be a guard or skid plate over the filter. Remove the guard and clean around the filters before removing them. Don’t skip cleaning around the filters. You do not want to introduce any dirt or other foreign materials into the transmission system. 
  • Remove Filters & Drain: Place an oil pan under one of the transmission filters. Unscrew the filter and let the oil drain. Repeat with the other transmission filter. Remove the drain pan and plan on bringing the old oil to your closest recycling center.
  • Install New Filters: Apply a thin layer of fresh transmission oil on the rubber seal of the new filters. Install the filters by turning clockwise. Once the filter makes a good connection to the filter adapter continue to turn about another 3/4 to full turn. 
  • Fill with Recommended Transmission Oil: Locate the expansion reservoirs. These are the little small plastic tanks on the top of your mower behind the seat.

    Clean around the reservoirs before you remove the caps. Fill with a good quality fresh 20W-50 or 15W-50 oil. (According to Gravely, either type of oil will work with Hydro-Gear transmissions used in their zero turns).

    Add oil through the expansion reservoirs until it reaches the “full cold” line on the tanks. You will have two tanks, one on each side of the mower.

    Some transaxles will have a vent plug located on each transaxle. Loosen this plug on each side. You will fill the transmission oil through the expansion reservoir until oil comes out of the vent plug. Tighten the vent plugs and continue fulling until the oil level reaches the “cold full” line on the expansion reservoir.
  • Purge Air Out of the Transmission System: It’s important to get all the air out of the system by going through some steps with the drive tires turning freely. In order to allow the drive wheels to turn freely, you will need to get the rear wheels off the ground. Do this by using jack stands to raise the rear of the mower just high enough so the wheels no longer touch the ground. 

    Open the bypass valves, start your mower, and increase the throttle to about ½ throttle. Release the parking brake. Move the speed levers forward and reverse slowly about 6 times in total. Repeat this process again with the bypass valves closed until your wheels begin to rotate at a normal rate and with a normal sound. Repeat as necessary to remove all air.

Let the transmission system cool and re-check your oil level. Add more oil if needed.

Step 10: Check Battery Clean the Battery Terminals

Clean any corrosion that has developed on your battery terminals using a baking soda and water solution consisting of 2 cups of water and 3 heaping tablespoons of baking soda.

Use a wire brush to remove the corrosion. Make sure your terminals are making a good connection. Add a dielectric grease to help prevent corrosion.

Test your lawn mower battery and charging system to make sure it is holding a charge. Refer to this guide for instructions on checking the charging system and battery.

Charge a Gravely Zero Turn Battery

  • Disconnect the battery cables from the battery. Remember: Positive cable (Red +) is the last one off and first one on. Now, if the battery has removable caps check the water level. If the plates inside the battery are not covered with water you will need to add distilled water to them. 

    Note: well water is not good for a battery. City water is a little better option, but it is best to use distilled water to your battery.
  • After checking the water level, hook the charger to the battery.
  • Check the battery voltage with your meter and see what it has in it. If the battery has 11.8 volts in it you won’t have to charge it very long. If it has 10.1 volts your battery is going to need to sit on a charger for a while. The lower the voltage reading, the longer your battery will need to sit on the charger.

    I like to put a very low battery on what is called a “slow bake”. Some battery chargers have different switches on them such as 6 amps, 4 amps, or 2 amps. Charge a very low battery on 2 or 4 amps and let it charge for about an hour.

    After an hour, check the reading to make sure the voltage rate is increasing. If it is, continue to charge for another hour. If it is not increasing it’s time to purchase a new battery. You can find a battery at your local lawn mower dealership, hardware store, or automotive parts store.

Step 11: Remove Debris Around Your Electrical Components and Wiring

Moisture can collect on the debris and in turn, start to corrode your electrical components and cause them to prematurely fail. Remove debris that has collected around your electrical components and wiring.

Step 12: Replace Your Fuel Filter

This is another filter that should be changed annually. Shut off your fuel supply using your fuel shut-off valve or crimp the fuel line. Remove your fuel filter and replace it with a new filter.

There should be an arrow on the filter housing. Your fuel filter needs to be installed with the arrow pointing in the direction of the fuel flow.

Step 13: Check the Fuel System

Check the fuel system for leaks. Follow the fuel line from your fuel tank up to the carburetor. Check the fuel line and components for leaks. Make sure the hose connections are tight and there are no leaks. Reference this article for all the places on your Gravely to check for a fuel leak.

Step 14: Check Your Mower’s Tire Pressures

A low tire can cause steering issues and an unleveled mower deck gives you a bad mowing experience. Check your tire pressures using a tire pressure gauge. Make sure your lug nuts are secure and the tire pressures are at the psi level recommended by Gravely.

Step 15: Remove Dirt and Debris from the Top of the Mower Deck

Debris can collect on your mower deck which can restrict the movement of your tensioner bracket and interferes with the movement of your belt around your pulleys. Dry debris on your mower deck increases the risk of fire when exposed to the heat and friction of the mower belt.

Place your mower deck at its lowest position. Remove the belt covers if the mower deck has them. Remove the debris under your pulleys and brackets and from the top of your mower deck.

If you are unable to gain access to the top of your deck to clean and check your components, you may have to remove them. Follow the instructions in your owner’s manual for instructions on removing your deck.

Step 16: Check the Pulleys and Belts

Now that the top of your mower deck is clean, check the pulleys and belts on your mower deck to ensure they are in good condition. A worn belt must be replaced.

Signs of a wearing belt include cracking, a shiny glazed appearance, and shredding. A belt that has been stretched and no longer sits tight to the pulleys must also be replaced.

A pulley must sit flat and parallel to the deck. When a pulley doesn’t sit securely on the deck and there is some vertical movement, the pulley must be replaced. To check for a bad bearing, slowly spin each pulley by hand.

Feel for a restriction or a noise coming from the bearing. These are both signs of a bad bearing and the pulley will need to be replaced.

Clean any rust you find on the pulleys. Rust can dry out your belt causing it to be prone to breaking. Extremely rusty pulleys should be replaced.

Step 17: Scrape the Deck & Check Your Gravely Mower Blades

Gain access to the bottom of your Gravely mower deck. With a heavy pair of work gloves, grab each end of a blade and rock the blade up and down. You are checking for damage in the spindle housing.

When you feel extra play and movement or you hear a knocking sound because of this extra movement, disassemble your spindle housings to identify the problem. Most likely, the bearing has failed and needs to be replaced.

Remove and sharpen your blades if they are still in good condition. You will need to replace blades that are bent, have large gouges in them, or are extremely worn.

Very worn blades are ones where the ends of the blades begin to become rounded or the sail on the blade is thinner than the center of the blade.

Sharpen blades to put a sharp edge on the blade and to smooth out any small nicks in the blade edge. You can find instructions on sharpening and balancing your Gravely blades in my article here.

Scrape your Gravely mower deck to remove grass clippings and debris collecting under your mower deck using a deck scraper or wire brush. A plugged mower deck can cause your mower to give you an uneven cut. It will also put your engine under extra load.

Step 18: Replace Damaged, Worn, or Missing Parts

Carefully inspect your Gravely to make sure all your hardware is secure and not missing. Replace any worn or missing parts.

Step 19: Grease Lubrication Points

You must lubricate your Gravely to prevent the wearing of and freezing up of the mower components. Grease pivot points and your castor fork and castor wheel bearings. Locate any additional grease zerks on your mower and pump high-performance grease into the zerks.

Step 20: Wash Your Zero Turn Mower & Dry Completely

Remove debris from your mower and wash it using a garden hose. If using a pressure washer, do not use high pressure as this can cause damage to your sealed bearings.

Once you are finished, allow the mower to completely dry. Storing a mower with wet components can prematurely corrode your mower and cause electrical components to fail.

If you have a leaf blower available, blow air on your mower to remove water remaining on your Gravely. If you are fortunate enough to have a nice sunny day, place your mower in the sun to dry and evaporate the moisture from your components.

A light breezy day works well too. Read more about cleaning your mower in this article.

Step 21: Complete if Placing Your Zero Turn in Storage

I highly recommend completing the following steps when storing your Gravely zero turn during the off-season. This will help prevent potential problems that can develop over the winter season.

  • Stabilize Your Fuel: Because gasoline can break down very quickly, you must use a fuel additive when storing your Gravely to protect the fuel system. Ethanol in your gasoline attracts moisture. The ethanol and moisture mixture will separate causing running problems and gumming the fuel system. I like to use a fuel additive called Sea Foam. Read more about the advantages of Sea Foam here.

    If you choose not to use an additive to stabilize your fuel, you should drain your Gravely mower of all fuel so it doesn’t sit all winter. Once the fuel is removed, start your mower and let it run until it shuts off.
  • Fully Charge Your Battery: A fully charged battery will not freeze during winter. Test your battery and make sure it is fully charged for winter. You can also remove your battery and store it in a cool dry location away from freezing temperatures. Just make sure it is not stored near any combustible items. Read more about preparing your battery for winter in “A Guide to Winter Lawn Mower Battery Care”.
  • Use a Rodent Deterrent: Rodents can get into the garage and storage sheds. They can choose to make a home with your lawn mower. I have seen many mowers and lawn tractors over the years that have had extensive wire harness damage from rodents chewing on wires.

    I use a product called Grandpa Gus’s Rodent Repellent. It comes in both pouch and spray forms. It’s a small price to pay to protect your mower.

    I tuck the pouches in my mower, in the glove box of my recreational vehicle, and in my other equipment. I use the spray on the wiring harness in my mower, equipment, and on my trailers.

Still Experiencing Problems with Your Gravely Lawn Mower?

Own a lawn mower long enough, you’ll start running into problems with it starting, not continuing to run, smoking, leaking gas, giving a bad cut, vibrating, or another issue.

To help you save time and money, I have put together a guide to help you troubleshoot the next problem that develops on your Gravely mower.

You can find this guide at Common Gravely Lawn Mower Problems & Solutions.

If you are unsure how to perform diagnostics and repairs on your Gravely lawn mower safely, it’s best to have a professional complete the repairs.

This will help you avoid personal injury or additional damage to the mower. Your local Gravely lawn mower dealership or lawn mower repair shop will be able to help you solve your problem.