Rotary Mower Gearbox for Comer T-305J Replacement 83.8kW
The HZPT rotary mower gearbox is a heavy-duty replacement for Comer T-305J, designed for PTO-driven agricultural mowers. Built with hardened spiral bevel gears, it delivers up to 2,335 Nm torque and supports 540 / 1000 RPM input, ensuring stable power transmission for rotary cutters, pasture mowing, and roadside vegetation maintenance.
HZPT Rotary Mower Gearbox – Direct Replacement for Comer T-305J, 183.8 kW
Model: T-305J | Input: 540 / 1000 RPM | Output Torque: up to 2,335 Nm | Ratio: 1.20 – 1.35
✔ Max Torque 2,335 Nm
✔ 540 / 1000 RPM Input
✔ 1¾" Z20 Spline Shaft
Rotary Mower Gearbox Product Overview
The HZPT T-305J rotary mower gearbox is an industrial-grade power transmission unit engineered as a bolt-on replacement for the original Comer T-305J gearbox. Built from high-alloy cast iron housing and precision-hardened steel gears, this rotary mower gearbox handles continuous input power of 183.8 kW while delivering peak blade shaft torques of 2,335 Nm—numbers that match or exceed the OEM specification without the OEM price tag.
Designed primarily for tractor-mounted rotary cutters and flail mowers, the gearbox accepts PTO input via a 1¾" 20-spline shaft (Z20) and steps up speed through fixed gear ratios of 1.20 : 1 or 1.35 : 1, depending on the configuration selected. The planetary-influenced gear arrangement keeps noise below 78 dB(A) under rated load and significantly reduces vibration transmitted back to the tractor drivetrain. An integrated oil-splash lubrication circuit, SAE 80W-90 GL-4 compatible, maintains consistent film thickness across all operating temperatures from −10 °C to 80 °C.
Each unit ships with pre-filled gear oil, a slip-clutch-compatible input interface, and all mounting hardware required for a direct swap on Comer T-305J-equipped machines. No machining. No adapters. No guesswork.
Rotary Mower Gearbox for Comer T-305J Replacement
Rotary Mower Gearbox Technical Specifications
All values at rated continuous duty. Shaft dimensions follow ISO 5211.
| Ratio (i) | Input Speed N₁ [RPM] | Input Power P₁ [kW] | Output Torque M₂ [Nm] | Shaft Type X | Shaft Type Y | Shaft Type Z | Input Side |
|---|---|---|---|---|---|---|---|
| 1.35 | 540 | 183.8 | 2,335 | 1¾" Z20 | 1¾" Z20 | 1¾" Z20 | X |
| 1.20 | 1000 | 183.8 | 2,043 | 1¾" Z20 | 1¾" Z20 | 1¾" Z20 | X |
| 1.35 | 1000 | 183.8 | 2,298 | 1¾" Z20 | 1¾" Z20 | 1¾" Z20 | X |
* Shaft Type X = Standard output. Alternate shaft options Y and Z available on request. Oil type: SAE 80W-90 GL-4.
What Is a Rotary Mower Gearbox — and Why Does Yours Need to Handle 2,335 Nm?
A rotary mower gearbox is the mechanical brain sitting between your tractor's PTO shaft and the cutting deck. Its job is deceptively simple: take the rotational input from the PTO (540 or 1000 RPM), multiply torque to the level the blade spindle demands, and keep the engine shielded from the shock loads generated every time a blade hits a rock, root, or thick brush stem.
The T-305J rotary mower gearbox sits in the high-demand tier of this category. At a 1.35 ratio and 540 RPM input, it puts out 2,335 Nm of torque—enough to drive large-diameter blade assemblies on 2.5–3.5 m cutting-width machines without thermal runaway or fatigue cracking at the gear flanks. The planetary-style bevel gear set inside distributes tooth load across multiple contact points simultaneously, which is why this unit runs cooler and quieter than conventional single-pair bevel boxes at the same power level.
In short: if your Comer T-305J has failed, is showing housing cracks, or simply has too many hours on it, the HZPT replacement rotary mower gearbox gives you the same mounting footprint, same shaft dimensions, and same rated power—at a fraction of the cost of an OEM unit.
Where This Rotary Mower Gearbox Gets the Job Done
🌾 Agricultural Field Mowing
Roadside verge maintenance, hay field trimming, and cover-crop termination on fields where blade speed consistency directly affects cut quality. The 183.8 kW rating handles 100+ hp tractors at full PTO engagement.
🌿 Pasture & Rangeland Management
Thick brush, saplings up to 25 mm diameter, and uneven terrain put extreme intermittent shock into the gearbox. The integrated torque buffer and hardened spiral bevel gears absorb those spikes without stripping teeth.
🏗️ Municipal & Infrastructure Maintenance
Highway shoulders, drainage canal banks, and airport perimeter vegetation control. Continuous-duty cycles demand a gearbox lubrication system that stays effective across temperature swings—this unit's oil-splash circuit manages it without external cooling.
🔧 OEM Retrofitting & Fleet Repair
Equipment dealers and agricultural machinery repair shops sourcing a cost-effective, spec-matched replacement for Comer T-305J units across customer fleets. Bulk pricing available for B2B orders of 10+ units.
Installation Guide – Replacing a Comer T-305J Rotary Mower Gearbox
Estimated time: 45–90 minutes with standard hand tools. Always disconnect PTO and engage parking brake before starting.
- Disconnect the PTO shaft — Slide the PTO yoke off the tractor's output shaft. Secure the free end so it cannot drop onto the gearbox housing.
- Drain old gear oil — Remove the drain plug on the existing T-305J gearbox. Allow full drainage (approx. 0.8–1.0 L). Dispose of used oil per local regulations.
- Remove the blade assembly — Lower the cutter deck to the ground. Remove the blade bolt(s) and slide the blade(s) off the output spindle. This relieves spring tension on the output shaft seal.
- Unbolt the old gearbox — Four M14 flange bolts secure the T-305J housing to the cutter deck frame. Mark the orientation before removal to match during reinstallation.
- Inspect the mounting face — Clean the deck mounting surface. Check for cracks or warping exceeding 0.5 mm. A warped face can misalign the new gearbox and cause premature bearing failure.
- Mount the HZPT replacement — Align the new rotary mower gearbox to the marked orientation. Torque M14 bolts to 95–110 Nm in a cross pattern using a calibrated torque wrench.
- Reinstall the blade assembly — Thread blade bolt(s) finger-tight first, then torque to manufacturer spec (typically 180–220 Nm for single-blade spindles).
- Fill with gear oil — Add SAE 80W-90 GL-4 oil through the fill port until oil reaches the level plug. Capacity: approximately 0.9 L. Re-install both plugs.
- Reconnect the PTO shaft — Slide the yoke fully onto the input shaft until the locking pin engages. Confirm free movement through full articulation range.
- Run-in check — Engage PTO at low idle (600 RPM) for 3 minutes. Listen for abnormal noise. Increase to working RPM and verify smooth operation. Recheck all bolt torques after the first 8 operating hours.
Frequently Ordered Together
These three components are commonly paired with the T-305J rotary mower gearbox for a complete drivetrain service or upgrade:
⚙
PTO Drive Shaft with Overrunning Clutch
1¾" Z20 spline, 1000 mm collapsed length. The overrunning clutch prevents blade inertia from back-driving the tractor PTO when you disengage—a key cause of T-305J gear failure when not fitted. CE-certified to Category 6.
Recommended pairing
🔩
Gearbox Input Shaft Seal Kit
Full set of NBR and FKM lip seals, O-rings, and gaskets sized for the T-305J housing bore. Replacing seals during gearbox installation costs 12 minutes; replacing a leaking seal on a mounted gearbox costs 90 minutes. Do the math once.
🛡
Hardened Rotary Cutter Blade Set
Brinell 400 HB chrome-molybdenum steel blades, balanced to ±3 g. Worn or unbalanced blades create vibration loads that can reduce rotary mower gearbox bearing life by 30–40%. Always replace blades when replacing the gearbox.
Recommended pairing
Frequently Asked Questions
What Customers Are Saying
★★★★★
"We run a fleet of 14 Kuhn FC rotary mowers for municipal roadside contracts. Three Comer T-305J units cracked housings in the same season—classic fatigue from improperly sized blades by the previous contractor. We replaced all three with HZPT units. Eight months later, 400+ hours on each, zero issues. The bolt-on fit was exact; our mechanic completed each swap in under an hour. The 2,335 Nm torque rating gives us headroom we didn't have with the originals."
— James R., Fleet Maintenance Manager, Midwest Municipal Services
★★★★★
"My old Comer gearbox finally retired itself—loudly, dramatically, in the middle of a 40-acre field, two days before hay season. My therapist calls it 'catastrophic failure.' I call it $800 of unscheduled vacation planning. Found the HZPT T-305J replacement, ordered it Thursday, installed it Saturday morning before my second coffee. Bolted right on like it was born there. Finished the field the same afternoon. My tractor hasn't been this happy since the Obama administration. Five stars. Would trauma-bond again."
— Dale T., Row Crop & Hay Producer, central Kansas
Stop Losing Field Time to a Failed Gearbox
The HZPT T-305J rotary mower gearbox ships ready to install, pre-filled, and built to the same power rating as the Comer original — at a price that makes stocking a spare unit sensible, not extravagant.
Fast shipping · B2B volume pricing available · 12-month warranty · Engineering support included
