Posted by Staff on 5/20/2026 to
Guides
Hydro-Gear Parts Quick Reference
A shop reference for identifying transaxle models, stocking common service parts, and cross-referencing OEM part numbers across brands including Scag, Exmark, Wright, and Gravely.
Important: Always read the Hydro-Gear model string off the transaxle housing sticker before ordering any part. Machine model alone is not always sufficient — multiple transaxle variants can exist within the same product line.
Transaxle Model Guide
Hydro-Gear makes a family of integrated zero-turn transaxles. The model number indicates the grade, displacement, and serviceability.
| Model | Grade | Max Machine Wt | Key Features |
|---|---|---|---|
| EZT | Residential | — | Sealed/non-serviceable. No fluid or filter change possible. Not recommended for commercial or large-acreage use. |
| ZT-2100 | Residential | ~700 lb | Serviceable. Entry residential/light prosumer. Found on Exmark Quest E-Series. |
| ZT-2800 | Estate / Heavy Residential | ~1,000 lb | Serviceable (fluid + spin-on filter). Stamped gears. Found on Scag SZL, some Gravely models. |
| ZT-3100 | Entry Commercial | ~1,100 lb | Cut gears — more durable than the 2800. Scag Patriot, Gravely ZT HD, some Exmark models. |
| ZT-3200 | Entry Commercial | ~1,100 lb | Same family as the ZT-3100, introduced as an upgrade option on select models. |
| ZT-3400 | Full Commercial | ~1,300 lb | Heavy-duty shaft. Scag Patriot/Tiger Cat, Exmark Lazer Z, Wright Stander X. |
| ZT-5400 | Full Commercial | ~1,500 lb | Top-tier integrated unit. Scag Turf Tiger II, Gravely Pro-Turn 200/400. |
| G700 | Heavy Commercial | Heavy | Separate pump and wheel motor architecture. Heavy commercial and stand-on applications. |
The ZT-2800 is the smallest unit with a serviceable fluid and spin-on filter. The ZT-3100 and up use cut gears for added durability. The ZT-3400 and ZT-5400 are the full-commercial units for production equipment.
Common Service Parts
Filters
| HG Part # | Description | Fits | Cross-References |
|---|---|---|---|
| 52114 | Spin-on transmission filter | ZT-2800, ZT-3100, ZT-3200 | Fits Toro, Snapper, Exmark, Ariens (spin-on style). Replace every 200–250 hrs or annually. |
| 71943 | Filter kit with O-ring (cartridge style) | ZT-3400, ZT-5400 | Scag: HG71943 · Gravely: 21548300 · Bad Boy: 603-1070-00 · Ferris: 5101987X2YP · Also: 72537 |
Key distinction: The 52114 (spin-on) and 71943 (cartridge kit with O-ring) are not interchangeable. The ZT-2800/3100 use the spin-on 52114; the ZT-3400/5400 use the cartridge-style 71943.
Seal Kits
| HG Part # | Description | Fits | Cross-References |
|---|---|---|---|
| 70525 | Pump overhaul seal kit (BDP-10 pumps) | BDP-10 series pumps | Exmark: 105-6184, 103-2766 · Ariens: 59203600 · Stens: 025-067. When replacing a pump, always replace the wheel motor, flush lines, and install a new filter. |
| 73190 | Seal kit (Scag-branded) | ZT series (Scag applications) | Scag p/n HG73190. Confirm the exact unit before ordering. |
Fan Kits
| HG Part # | Description | Fits | Notes |
|---|---|---|---|
| 70579 | 7" fan kit with washer and nut | ZT-2800, ZT-3100, ZT-3400 | Also sold in 2-packs. Check fan size — some units use 10" fans. |
| 50848 | 10-blade fan, 7" | Various ZT / P-Series pumps | Confirm fan diameter against unit spec before ordering. |
O-Rings, Tubes & Tanks
| HG Part # | Description | Fits | Notes |
|---|---|---|---|
| 54501 | Triple O-ring charge tube | ZT series | A frequent leak source. Sold in 6-packs. Inspect whenever the customer reports fluid loss. |
| 71938 | Expansion tank and cap, 1000 mL | ZT-3400, ZT-5400 | Ariens: 03947000. Check for cracks and cap seal condition at every service. |
Rebuild & Repair Components
| HG Part # | Description | Fits | Notes |
|---|---|---|---|
| 70690 | Center section kit | BDP-10 pumps | Major rebuild component. Includes relief valve, check valves, and charge pump parts. |
| 71840 | Purge valve kit | ZT-2800, ZT-3100, ZT-3400 | Used for air purging after fluid change. Some units have external purge ports; others require loosening the bypass valve. |
| 72490 | Brake assembly kit | ZT series | Inspect brake linkage and spring tension when a mower creeps in neutral. |
Brand Fitment Reference
Common transaxle assignments by brand and machine line. Always verify by reading the Hydro-Gear model string off the unit.
| Brand | Machine Line | Typical HG Unit | Notes |
|---|---|---|---|
| Scag | SZL 61" | ZT-2800 / ZT-3100 | Depends on model year and configuration. |
| Scag | Patriot | ZT-3100 / ZT-3400 | Filter kit: Scag p/n HG71943 = Hydro-Gear 71943. |
| Scag | Tiger Cat II | ZT-3400 | — |
| Scag | Turf Tiger II | ZT-5400 | Filter kit: HG71943. |
| Exmark | Quest E-Series | ZT-2100 | Exmark p/n 119-3331. |
| Exmark | Lazer Z | ZT-3400 | Seal kit: Exmark 105-6184 = HG 70525. |
| Exmark | Turf Tracer (hydro walk-behind) | BDP-10L pump | Pump p/n BDP-10L-117P. Cross-refs Scag 48551. |
| Wright | Stander X / ZK | ZT-3400 | Confirm Aero Core vs. non-Aero Core before ordering Qwikchute or deck accessories. |
| Wright | Stander (standard) | ZT-3100 / ZT-3400 | Verify by model string on unit. |
| Gravely | ZT HD | ZT-3100 | Filter kit: Gravely 21548300 = HG 71943. |
| Gravely | Pro-Turn 200 / 400 | ZT-5400 | Gravely p/n 03935200 (RH) / 03935300 (LH). |
| Ferris | Various | ZT-3100 / ZT-3400 | Filter kit: Ferris 5101987X2 = HG 71943. |
| Bad Boy | Various | ZT-3400 / ZT-5400 | Filter kit: Bad Boy 603-1070-00 = HG 71943. |
Additional Resources
- Hydro-Gear Cross-Reference Guide — Decode any model string prefix at hydro-gear.com/cross-reference-guide
- Service & Repair Manuals — Free downloads at hydro-gear.com/service-repair-manuals
- Illustrated Parts Lists — Exploded views available at Jack's Small Engines and LawnMowerPros
