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Maintaining or restoring the performance of your Twin Disc MG5114A marine transmission means understanding what parts are most likely to fail, when to replace them, and how to rebuild the gear using premium aftermarket components. Whether you’re doing routine service, a complete teardown, or replacing a failed unit altogether, having the right parts—and knowing when to use them—is key to uptime, cost savings, and vessel safety.
This guide covers the most common parts to replace, how to choose a rebuild kit, and when it makes sense to go with a completely rebuilt MG5114A transmission.
Parts Catalog for Twin Disc MG520 Marine Transmissions
Plate Kit For Twin Disc MG520 Marine Transmission
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Most Common Replacement Parts
The MG5114A is built for thousands of hours of operation under high loads—but like all mechanical equipment, it eventually wears. Over time, parts that are subjected to heat, friction, pressure, or vibration will degrade and require replacement.
Here’s a breakdown of the most commonly replaced internal components:
Clutch Discs and Separator Plates
Clutch Discs (Friction Plates)
The clutch discs are the most critical wearable parts inside the MG5114A. These discs engage and disengage the forward and reverse gears using hydraulic pressure. Over time, they wear down due to:
- High load cycling
- Improper oil viscosity
- Overheating due to pressure loss
- Aggressive shifting or maneuvering
Symptoms of worn clutch discs include:
- Slipping in forward or reverse
- Delayed engagement
- Burnt or dark transmission oil
- Reduced propulsion under load
Best Practice: Always replace clutch discs as a full set. Mixing old and new plates causes uneven engagement and premature wear.
Separator Plates (Steel Plates)
These steel or composite plates sit between each clutch disc and help distribute pressure. While they don’t wear as quickly, they can:
- Warp under high heat
- Get scratched or scored
- Develop hot spots or glazing
Separator plates should be replaced if:
- They show signs of discoloration or heat marking
- They’re no longer flat when checked on a straight edge
- A clutch failure has contaminated the pack
At Diesel Pro Power, replacement kits include matched sets of friction and separator plates to restore factory-calibrated friction balance.
Gaskets and Seals
The MG5114A has multiple sealing surfaces designed to keep hydraulic oil in and contaminants out. These include:
- Input shaft seal
- Output shaft seal
- Side access cover gaskets
- Oil pan gasket
- Selector shaft seals
- Cooler port O-rings and banjo seals
- Vent cap and breather grommets
Even a small leak at any of these seals can lead to:
- Loss of hydraulic pressure
- Overheating
- Clutch failure due to aeration
- Bilge contamination
Pro Tip: Replace all seals and gaskets any time the transmission is removed, serviced, or rebuilt.
High-quality rebuild kits from Diesel Pro Power include:
- Heat- and pressure-rated gaskets
- Double-lip shaft seals
- Viton or nitrile O-rings for cooler fittings
Bearings and Thrust Washers
Bearings
The MG5114A contains multiple internal bearings supporting:
- The input shaft
- Intermediate gears
- Output shaft
- Pump gear
Bearings should be replaced if they show:
- Scoring or pitting
- Rough rotation
- Excessive radial play
- Heat damage or discoloration
These failures are often silent at first but can quickly escalate to:
- Gear noise
- Misalignment
- Shaft damage
- Catastrophic internal failure
Always use marine-rated, high-load bearings that match OEM tolerances and load capacity.
Thrust Washers
These control axial movement of rotating shafts and gears inside the transmission. When worn:
- Endplay increases
- Gears misalign
- Oil leaks develop at mating surfaces
- Engagement becomes noisy or incomplete
Thrust washers are cheap—but failure to replace them can cost a rebuild.
Recommended Rebuild Kits
When overhauling the MG5114A, it’s more efficient and reliable to replace all critical wearable components as a set. This is where rebuild kits come in.
What’s Included in a Typical Rebuild Kit
At Diesel Pro Power, MG5114A rebuild kits are engineered to match OEM specs and include:
- Full clutch pack (forward and reverse): all friction and separator plates
- Complete gasket set: input/output seals, access covers, oil pan, selector shaft
- Oil seals and O-rings for all service points
- Pump seals and gaskets
- Vent filter or breather cap components
- Snap rings and thrust washers where applicable
- Sealants and assembly guides (depending on kit level)
You get everything needed for a proper transmission overhaul—without paying OEM prices.
OEM Match Aftermarket Options from Diesel Pro Power
All Diesel Pro Power kits are:
- Precision-manufactured to OEM tolerances
- Designed for long-term saltwater resistance
- Compatible with SAE 30 or 40 monograde marine oils
- Used by fleet operators, shipyards, and independent rebuilders worldwide
Why choose Diesel Pro Power?
- Immediate shipping worldwide
- No need for serial numbers or dealer gatekeeping
- Kits built specifically for marine performance and durability
- Telephone and email support from experienced marine techs
When to Choose a Full Rebuild vs. Component Service
| Scenario | Recommendation |
| Slipping in one gear, oil is clean | Replace clutch pack only |
| Oil leaking at seals, but clutch holds well | Seal and gasket kit only |
| Gear noise, endplay, or bearing roughness | Full rebuild kit with bearings |
| Unknown hours, burned oil, or vibration | Complete rebuild |
| Gear was submerged or contaminated | Rebuild or full replacement |
For commercial operators, rebuilding during dry dock avoids emergency failures at sea—and saves thousands in tow, labor, and downtime.
Complete Rebuilt Transmissions
When time is limited or your unit has suffered major internal failure, a complete rebuilt MG5114A transmission can save time and money.
Advantages for High-Hour or Damaged Units
Some units aren’t worth rebuilding in the field—especially when:
- Gear teeth are chipped or missing
- Shafts are worn beyond spec
- Housings are cracked or warped
- It’s the vessel’s only propulsion system, and time is critical
Benefits of a Diesel Pro Power rebuilt transmission:
- Zero-hour ready-to-install transmission
- New clutch packs, bearings, seals, and precision-checked components
- Bench-tested before shipment
- Backed by an OEM-matching warranty
- No surprises—what you see is what you get
Ships fast, installs clean, and gets you back in operation with peace of mind.
When a Replacement Is More Cost-Effective Than a Repair
| Condition | Recommendation |
| Unit has >15,000 hours and worn case bores | Replace |
| Clutch, gear, and bearing failures all at once | Replace |
| Emergency timeline (charter boat, towboat, etc.) | Replace |
| Engine repower underway and old gear is marginal | Replace |
| Rebuild quote exceeds 60% of replacement cost | Replace |
Tips for a Successful Rebuild
- Work clean – Use lint-free rags, sealable trays, and solvent baths
- Use a full kit – Mixing old and new parts causes poor clutch balance
- Take photos during disassembly – Helps with orientation during reassembly
- Replace all seals, even if not leaking – A rebuild is your only window
- Use correct tools – Presses, seal drivers, and micrometers are a must
- Inspect shafts, bores, and covers for wear – Don’t trap failure inside a rebuild
- Torque all fasteners – Never guess—always verify with a calibrated wrench
Frequently Asked Questions
Q: How many hours is a rebuild kit good for?
A: Diesel Pro Power kits are designed to last 5,000–10,000 hours, depending on load, oil quality, and cooling.
Q: Do I need the serial number to order parts?
A: No. Diesel Pro Power matches parts by model and gear ratio. You can contact our team if unsure.
Q: Can I reuse separator plates?
A: Not recommended. Warped or scored plates ruin new clutches. Always replace them together.
Q: What oil should I use after a rebuild?
A: Use SAE 30 or SAE 40 non-detergent oil. Synthetic or multi-grade oil is not recommended unless approved.
Final Thoughts on Rebuild Kits and Parts Replacement
The Twin Disc MG5114A is an exceptional marine transmission, but like any mechanical system, its performance and longevity depend on proactive service and quality parts. Whether you’re doing a clutch-only refresh, replacing leaking seals, or performing a complete overhaul, you need a kit that’s built for the job—and the right guidance behind it.
- Always replace in matched sets
- Don’t ignore seals, bearings, or washers
- Use rebuild kits to save time and ensure part compatibility
- Consider a rebuilt unit when damage is extensive or uptime is critical
- Trust premium aftermarket kits like those from Diesel Pro Power
With proper parts, expert service, and support from our team, your MG5114A will be ready to deliver thousands of reliable hours for any marine application—whether pushing barges, hauling nets, or navigating tight channels.
Parts Catalog for Twin Disc MG520 Marine Transmissions
Plate Kit For Twin Disc MG520 Marine Transmission
Gasket Kits For Twin Disc MG520 Marine Transmission
