<img height="1" width="1" style="display:none" src="https://www.facebook.com/tr?id=585148855567101&amp;ev=PageView&amp;noscript=1">

Transmission Oil
Performance System (TOPS)

TOPS brings enhanced drivetrain protection and performance to Walker Mowers equipped with Walker Model 7 hydrostatic transmissions by actively circulating and filtering the transmission system fluid every 38 seconds.

  • A fully-machined, billet aluminum oil pump with integrated filter mount is driven by transmission drive belt and circulates filtered oil when engine is running
  • Filter with premium fiberglass media made in the USA for Walker
  • Remote steel oil reservoir increases oil capacity by 100% and reduces oil temperature
  • Fully synthetic oil formulated specifically for extended transmission life under high loads and in extreme ambient temperatures
  • ISO-VG 220 viscosity oil for superior protection and performance
  • Maintenance schedule adds 500-hour oil and filter change interval after the initial 100-hour break-in service
  • Extended transmission warranty when serviced as directed, conditions apply




What is the Walker TOPS System

Ted Walker, VP Engineering for Walker Manufacturing, talks us through the new Transmission Oil Performance System (TOPS) from top to bottom, beginning to end.

0:00 - What is TOPS?
0:46 - TOPS component identification
2:24 - What does TOPS do?
7:41 - How was TOPS developed?
11:16 - What is maintenance like for TOPS?
13:15 - TOPS Warranty
14:22 - TOPS oil change process
15:28 - How do you get TOPS?

TOPS™ Benefits

Active filtration reduces contamination and wear to transmission components check mark
Doubles hydrostatic drive system oil capacity for increased oil life check mark
Superior protection in high duty cycle applications and high ambient temperatures check mark
Improved system cooling check mark
500 hour oil change interval check mark
Extends your Walker hydrostatic transmission warranty with Walker check mark


  • Walker Model 7 Hydro Oil
  • 2.75 US Quart (2.4 L) system capacity
  • Fully synthetic oil for superior lubrication and long life
  • More durable fluid film than conventional oils for improved wear protection
  • ISO-VG 220 viscosity for improved lubrication across broad temperature range
  • Increases safe oil operating temperature range by nearly 100°

TOPS™ Oil Filter

  • Premium fiberglass media provides extra capacity with superior filtration
  • Effectively protects against contaminants greater than 10 microns
  • Prevents cross contamination between hydrostatic transmissions
  • High durability, anti-drain back valve & sealing gasket
  • High quality, made-in-USA filter

3 year unlimited hour warranty badge graphic

TOPS™ Extends Your Warranty

Walker Model 7 hydrostatic transmissions are covered by a three (3) year or 3000 hour (whichever comes first) warranty for Model 7 Hydrostatic transmissions. This covers full cost of replacement up to 1000 hours of use, and after 1000 hours warranty coverage is prorated against 3000 hours. 

Walker will extend the transmission warranty to 3 years, unlimited hours if the transmissions are serviced by an authorized Walker Dealer at the recommended intervals using only Walker recommended oil and filters. Conditions apply, see your Walker Dealer for details.

Note: TOPS™ components are covered by the tractor's 2 year warranty. 

Service Information and Resources


TOPS™ Service Schedule



500 Hours
oil change mark oil change mark oil change mark oil change mark

The TOPS™ filter and the oil must be changed after the first 100 hours, at 500 hours, and every 500 hours thereafter. Walker Model 7 hydrostatic transmissions ship from the factory with TOPS™ Walker Model 7 Hydro oil. TOPS™  Walker Model 7 Hydro Oil is the only factory approved transmission fluid for servicing the transmissions in this tractor due to its improved performance.


TOPS™ Compatibility

Model Compatibility
C19 check mark
C19i check mark
Model Compatibility
T23 check mark
T27i check mark
D21d check mark


  • TOPS™ comes standard on Model C19, C19i, T, and D machines produced after S/N 2021-168381
  • TOPS™ conversion kit is available for previous Model C, T, and D machines after S/N 2015-134121

Oil and Filter Ordering Info

Walker Model 7 Hydro Oil 1 U.S. Quart (946 mL) Walker P/N 6450-21

Walker Model 7 Hydro Oil
1 U.S. Quart (946 mL)
Walker P/N 6450-21

Kohler PRO Oil Filter

Oil Filter
Walker P/N 5024-13

Checking Model 7 Hydrostatic
Transmission Fluid Level

The Model 7 hydrostatic fluid level should be checked after every 25 hours of machine operation. Always perform this check when the machine is cold.

  1. Park the mower on a level surface. Stop the engine and wipe dirt and contaminants from around the base of the reservoir to better see the COLD mark.
  2. The level of the oil can be seen through the observation window on the rear of the reservoir. The oil fill line should be around the mid-way point of the observation window.
  3. If the fluid is below the mid-way point, add oil using Walker P/N 6450-21. Thoroughly clean around the reservoir fill cap before removing the cap. Add oil until the fluid is at the mid-way point. Reinstall the cap and tighten until secure.

NOTE: If you regularly are running a bit low, it is likely there is a leak. Contact your authorized Walker Dealer for inspection and repair.

Changing Transmission
Fluid (Oil) and Filter

The filter and the oil must be changed after the first 100 hours, at 500 hours, and every 500 hours thereafter. The Model 7 transmissions ship from the factory with Walker Model 7 Hydro Oil. Walker Model 7 Hydro Oil is the only factory approved transmission fluid for servicing the transmissions in this tractor due to its improved performance.

  1. Remove the deck from the tractor.
    IMPORTANT: Thoroughly clean around each cap, connector, and plug on the reservoir and the transmissions. Do not allow contaminants to enter the system during this process which could lead to damage and premature failure.
  2. Drain the oil from the reservoir through the bottom plug on the rear of the reservoir.
  3. Drain the oil from each transmission through the elbow connector on the bottom by removing the line that runs from the reservoir to the transmission.
  4. Remove the filter.
  5. Install the new filter. Lubricate the filter gasket with a drop of fresh oil. Turn the filter clockwise until the rubber gasket contacts the sealing surface, then turn an addition 3/4 turn. Do not over-tighten.
    NOTE: Use ONLY a Walker filter (P/N 5024-13).
  6. Reconnect the lines between the reservoir and the transmissions at the elbow connectors. Use a 12mm wrench on the hose collar to prevent the hose from twisting while tightening these connections.
  7. Reinstall the reservoir drain plug using a liquid thread sealer.
  8. Thoroughly clean the area around each fill plug on the top of each transmission. Remove the fill plugs, and use a small funnel to fill to the bottom of the threads—approximately 16 oz. Reinstall the fill plugs.
    NOTE: Use ONLY Walker Model 7 Hydro Oil (P/N 6450-21).