Disassembly Procedures For Twin Disc MG-540 Marine Gear

May 23, 2025


Introduction to Disassembly For Twin Disc MG-540 Marine Gear

The MG-540 marine transmission is a heavy-duty unit designed for long-term durability and high torque output. When disassembly is required—whether for overhaul, inspection, or replacement of internal components—it must be done in a clean, well-equipped facility by trained technicians. Proper disassembly ensures safe operation, preserves component integrity, and prepares the transmission for effective reassembly.

This guide outlines the complete disassembly process, focusing on:

  • External component removal
  • Input and output shaft disassembly
  • Clutch shaft and pinion gear extraction
  • Proper handling of seals, o-rings, and fasteners
  • Recommended torque values and precautions

Important Note: Before disassembly, disconnect power and follow complete lockout/tagout procedures. Drain all fluids, and have appropriate lifting equipment available, as many components are heavy and precision-machined.

External Component Removal For Twin Disc MG-540 Marine Gear

Step 1: Drain the Transmission

  1. Drain the transmission oil by removing the 1-15/16″-12 hex plug from the bottom of the housing.
  2. Remove the drain plug from the bottom of the heat exchanger (if equipped) and allow full drainage of the system.
  3. Collect and dispose of used oil in accordance with marine environmental regulations.

Step 2: Disconnect External Lines and Hoses

  • Label and disconnect hydraulic lines.
  • If the unit uses the EC050 or electric valves, unplug solenoid wiring and sensors.
  • Mark hoses and electrical connectors for ease during reassembly.

Step 3: Remove Filters and Heat Exchanger

  • Remove the oil level dipstick and tube.
  • Detach the high-pressure and lube oil filters by unscrewing their mounting bolts.
  • Remove the heat exchanger if present.

Step 4: Remove Top Cover and Oil Pumps

  • Unscrew twenty-four 1/2-13 x 1.5 capscrews and remove the top cover.
  • Remove the oil pumps (both pressure and lube) by removing their retaining capscrews.

Step 5: Rotate Transmission

  • Use blocks to safely rotate the transmission with the input end facing upward.
  • Confirm the transmission is securely blocked to prevent rolling or tipping.

Step-by-Step Disassembly of Input and Output Shaft Assemblies

Input Shaft and Gear Removal

  1. Remove Input Coupling: Flatten the lock plate and remove three 1/2-13 x 1.5 capscrews. Use a hydraulic puller to detach the coupling or rubber block drive from the tapered shaft.
  2. Remove Input Seal Retainer: Unscrew and remove the retainer using five 1/2-13 x 1.5 bolts.
  3. Remove Bearing Retainer: Remove the bearing retainer for the input driven gear using another set of five 1/2-13 bolts.
  4. Detach Front Input Housing: Remove seventeen 1/2-13 x 1.5 bolts holding the front input housing. Use jacking screws to carefully separate and remove the housing. Extract the lube valve from the front housing.
  5. Extract Input Gears: Remove both input driving and driven gears. Remove bearings only if they show signs of wear or failure.

Output Shaft Disassembly

  1. Remove Output Clamping Plate: Flatten the lock plate and remove three 1-14 x 2 bolts holding the output flange clamping plate.
  2. Remove Oil Catcher: Remove six 5/16-18 capscrews securing the output bearing oil catcher.
  3. Remove Bottom Cover: Unscrew twenty-four 1/2-13 capscrews from the bottom housing. Break the Loctite seal before lifting the cover.
  4. Extract Output Bearing Retainer: Remove the screw holding the outer race of the output bearing.
  5. Rotate Unit: Reposition the transmission so the output end faces up, and secure it.
  6. Remove Output Gear and Shaft:
    • Use blocks to support the output gear before separating it.
    • Use a hydraulic hollow ram and puller to remove the shaft from the taper. Up to 50 tons of force may be required.
    • Remove bearings only if replacement is necessary.

Pinion Gear and Clutch Shaft Removal For Twin Disc MG-540 Marine Gear

Clutch Shaft Access and Disassembly

  1. Remove Suction Screens and Cover Assemblies: Remove the 3/8-16 capscrews to lift off the left and right cover assemblies and suction strainers.
  2. Remove Manifold and Pump Drive Adapters:
    • Unscrew thirteen 1/2-13 and one 5/8-11 bolts to remove the rear manifold.
    • Use a chisel to split the retaining sleeve on each clutch shaft.
    • Drive out the retaining pin and remove the pump drive adapters from each clutch shaft.
  3. Remove Lube Tube: Lift out the lubrication tube and gasket.
  4. Withdraw Clutch Shaft Assemblies: Clutch shafts can now be removed and moved to a workbench or disassembled in place. If using a bench, use spring compressors (Tool T-16240-3) to disassemble the spring-loaded clutch piston.

Clutch Disassembly Steps

  1. Flatten lock tabs and remove twenty-four 1/2-13 x 6 bolts holding the retaining plate.
  2. Compress the spring with a press or special tool.
  3. Remove snap ring, spring, and retainers.
  4. Extract inner and outer pistons, clutch plates, and seal rings.
  5. If required, remove the bearing cone from the cylinder.
  6. Remove clutch plates and backplate from transfer gear.

Pinion Gear Removal

  1. Flatten screw locks and remove six 1/2-13 x 4.5 bolts that hold the pinion bearing caps.
  2. Use jacking bolts to remove caps, then remove bearing cups.
  3. Install special tool T-16240-4 to remove the pinion and hub assembly.
  4. Remove retaining rings, shims, and oil catchers as needed.

Proper Handling of Seals, O-Rings, and Torque Specs For Twin Disc MG-540 Marine Gear

Seal and O-Ring Removal and Replacement

  • All seals, o-rings, and gaskets must be discarded and replaced during reassembly.
  • Tag and store old components with associated parts to track quantity and type.
  • Use Twin Disc-approved replacements and lubricate all o-rings lightly with clean transmission oil before installation.

O-Ring Tips:

  • Avoid twisting during installation.
  • Do not reuse any rubber sealing component.
  • Use plastic or wood tools—never metal picks—to remove o-rings.

Torque Specifications

Correct torque is critical to prevent component warping, fastener stretching, and premature failure. Refer to the following fastener torque chart for U.S. Standard threads:

Thread Diameter SAE Grade 5 Torque (lb-ft) SAE Grade 8 Torque (lb-ft)
1/4″ 6–8 10–12
3/8″ 25–29 35–41
1/2″ 60–70 83–97
5/8″ 120–140 165–195
3/4″ 205–245 295–345
1″ 495–585 715–835

All threads must be lubricated with a light film of oil prior to torquing.

Best Practices:

  • Use a calibrated torque wrench
  • Torque bolts in a criss-cross pattern when securing housings or covers
  • Document torque values and part replacements in maintenance logs

Conclusion

Disassembly of the Twin Disc MG-540 marine gear is an intensive process requiring attention to detail, proper tools, and methodical procedures. Every seal, shim, and fastener plays a role in transmission performance and safety. This section covered:

  • Safe and complete external component removal
  • Step-by-step disassembly of shafts, clutches, and gears
  • Precision handling of seals and fasteners
  • Torque best practices and tool recommendations

When executed correctly, this disassembly lays the groundwork for a successful inspection and eventual rebuild or reassembly. Always consult the OEM tolerances and use approved replacement parts to ensure continued reliability at sea.

Videos About Twin Disc Transmissions

6 Reasons Your Twin Disc Transmission Has Low Oil Pressure

7 Reasons Your Twin Disc Transmission Is Overheating

3 Reasons Your Clutch Plates in Your Twin Disc Transmission Are Making Excessive Noise

 

Bull Gear On A Twin Disc Transmission 

Rebuilt Twin Disc Transmissions

Please follow and like us:
error
fb-share-icon
Tweet
fb-share-icon
RSS
Follow by Email
Facebook
Twitter

Leave a Reply

Your email address will not be published. Required fields are marked *

(Wish we didn't have to do this, but there are too many bots on the internet)