50 FAQs About The Twin Disc MG518 Marine Gear

March 18, 2025

Parts Catalog for Twin Disc MG518 Marine Transmissions
Rebuilt Twin Disc MG518 Marine Transmissions
Plate Kit For Twin Disc MG518 Marine Transmission
Gasket Kits For Twin Disc MG518 Marine Transmission

1. What is the oil capacity of the Twin Disc MG518?

The Twin Disc MG518 marine gear has an oil capacity of approximately 3.5 – 5 quarts (3.3 – 4.7 liters), depending on the configuration and installation. Always check the oil level using the dipstick before operation.

2. What type of oil is recommended for the MG518?

The recommended oil for the MG518 is SAE 30 or SAE 40 non-detergent marine oil. Alternatively, some models can use Dexron III/Mercon ATF if specified by the manufacturer. Always refer to the service manual for specific recommendations.

3. How often should the oil be changed?

Under normal operating conditions, the oil should be changed every 500 hours or annually, whichever comes first. If operating under heavy loads or extreme conditions, oil should be changed every 250 hours.

4. What are common signs of transmission failure?

Difficulty shifting gears
Slipping transmission under load
Unusual noises (grinding, whining, or clunking)
Overheating or excessive temperature warnings
Leaking transmission fluid

5. How do I check for proper alignment during installation?

Use a dial indicator to measure misalignment.
Check for less than 0.002 inches (0.05mm) of misalignment in the input and output shafts.
Ensure the propeller shaft coupling aligns perfectly with the transmission output flange.

6. What torque specifications should be followed for mounting bolts?

Bellhousing Bolts: 75-90 lb-ft (102-122 Nm)
Output Flange Bolts: 60-80 lb-ft (81-108 Nm)
Mounting Bracket Bolts: 50-70 lb-ft (68-95 Nm)
Clutch Pack Bolts: 50-70 lb-ft (68-95 Nm)

7. How do I engage and disengage the gear properly?

Always shift gears at idle speed (600-800 RPM).
Engage the gear smoothly by moving the control lever in a steady motion.
Avoid shifting into reverse while the vessel is still moving forward.

8. What should I do if the gear won’t engage?

Check fluid levels and hydraulic pressure.
Inspect the shift linkage for misalignment.
Ensure the clutch pack is not excessively worn.
Test for hydraulic pump failure.

9. What are common causes of hydraulic failure?

Low hydraulic fluid levels
Clogged hydraulic filter
Air in the hydraulic system
Worn hydraulic pump

10. How do I troubleshoot overheating issues?

Ensure the oil cooler is functioning properly.
Check for low transmission fluid levels.
Inspect the oil filter for clogs.
Verify there are no blockages in hydraulic lines.

11. How can I reduce excessive vibration during operation?

Ensure proper shaft alignment.
Inspect the mounting bolts and engine mounts for tightness.
Check for worn-out bearings or couplings.

12. What’s the correct procedure for disassembly?

Drain all transmission fluid.
Remove the output shaft coupling and input shaft.
Disassemble the gear housing and clutch pack.
Use proper bearing pullers and snap ring pliers.

13. How do I replace the main seal?

Remove the output shaft.
Use a seal puller to extract the old seal.
Apply sealant and install the new seal evenly.
Reinstall the shaft and torque to specifications.

14. What is the expected lifespan of the MG518 under normal operation?

With regular maintenance and proper usage, the MG518 can last 15,000 to 20,000 operating hours before a major overhaul is needed.

15. How do I identify worn gears?

Look for chipped or pitted gear teeth.
Listen for grinding noises during operation.
Check for metal shavings in the oil.

16. How often should filters be replaced?

Transmission filters should be replaced every 500 hours or annually.

17. Can I use alternative lubricants?

Use only OEM-recommended fluids. Substitutes should meet API GL-4 or GL-5 gear oil specifications.

18. What are the symptoms of a faulty clutch?

Slipping gears
Difficulty engaging forward or reverse
Burnt oil smell

19. How do I test for proper fluid levels?

Use the dipstick with the transmission in neutral and the engine off.

20. How do I clean internal components safely?

Use non-corrosive degreasers and compressed air to remove debris.

21. What is the recommended maintenance schedule?

Daily: Check fluid levels
Weekly: Inspect for leaks and noises
Monthly: Verify torque on mounting bolts
Annually: Full fluid and filter change

22. How do I store the transmission long-term?

Drain oil and refill with rust-inhibitor oil.
Store in a dry, climate-controlled area.
Rotate shafts manually every six months.

23. What parts wear out the fastest?

Clutch friction plates
Oil seals
Bearings

24. How do I ensure proper cooling during operation?

Keep oil cooler clean and free of debris.
Ensure proper oil circulation.

25. Can I repair cracks in the housing?

Minor cracks can be welded or sealed.
Major cracks require replacement of the housing.

26. What tools are essential for disassembly?

Torque wrench
Bearing puller
Snap ring pliers

27. How do I align the output shaft correctly?

Use dial indicators to measure alignment.
Adjust the mounting shims if needed.

28. What safety measures should be followed during repairs?

Always disconnect power before working.
Use PPE like gloves and eye protection.

29. How do I check for leaks?

Inspect seals and gaskets.
Check for drips under the unit.

30. What causes grinding noises during gear shifts?

Worn clutch plates
Misaligned gear teeth

31. How should I handle contaminated oil?

Drain and replace immediately.
Inspect for metal particles.

32. What are the most critical inspection points?

Fluid levels
Gear teeth condition

33. How do I replace the hydraulic pump?

Drain hydraulic fluid.
Remove mounting bolts.
Install new pump and reconnect hoses.

34. What’s the proper tightening sequence for bolts?

Follow a cross-pattern for even distribution.

35. How can I detect internal damage?

Conduct oil analysis for metal particles.
Listen for abnormal noises.

36. How do I calibrate control systems?

Adjust shift linkage for proper travel range.

37. What’s the correct procedure for flushing the system?

Drain old oil.
Flush with clean oil before refilling.

38. How do I measure gear backlash?

Use feeler gauges between gear teeth.

39. What are best practices for emergency shutdown?

Reduce throttle to idle.
Shift to neutral.
Shut down the engine.

40. How can I improve component longevity?

Regular oil changes.
Proper cooling maintenance.

41. Where can I order aftermarket parts for the MG518?

You can order high-quality aftermarket parts for the Twin Disc MG518 Marine Gear directly from Diesel Pro Power (https://dieselpro.com/twin-disc-marine-transmission-parts). At Diesel Pro Power, we specialize in aftermarket replacement parts that meet or exceed OEM quality standards, ensuring reliable performance and durability.

We offer a wide range of replacement parts for the MG518, including:

Clutch packs
Oil seals and gaskets
Bearings and bushings
Oil filters
Complete rebuild kits

Our goal is to provide fast shipping and expert customer support, ensuring that you receive the right parts quickly and efficiently. We understand the importance of keeping your marine transmission running smoothly, which is why we stock high-quality aftermarket parts for the MG518 that are designed for long-lasting performance.

For any questions or assistance, visit Diesel Pro Power or contact our support team.

42. What are standard replacement intervals for seals?

Seals in the Twin Disc MG518 should be replaced at regular intervals to prevent fluid leaks and contamination.

Seal Type	Replacement Interval
Input Shaft Seal	Every 5,000 – 7,500 hours
Output Shaft Seal	Every 5,000 – 7,500 hours
Hydraulic Seal	Every 2,500 – 5,000 hours
Gaskets	During any major overhaul

If a fluid leak is detected before the replacement interval, replace the affected seal immediately to prevent further damage.

43. What should I do if fluid contamination is detected?

Contaminated transmission fluid can cause premature wear, overheating, and gear failure. If contamination is found:

Drain the transmission fluid completely.
Flush the system with a small amount of fresh oil to remove debris.
Replace the oil filter to prevent further contamination.
Inspect seals and gaskets for leaks that may have allowed contaminants in.
Refill with clean, manufacturer-approved fluid.

If contamination persists, consider sending a fluid sample for analysis to determine the cause.

44. How do I test hydraulic pressure?

To test hydraulic pressure in the Twin Disc MG518 Marine Gear:

Locate the test port on the hydraulic pump or control valve.
Attach a hydraulic pressure gauge rated for at least 500 psi.
Start the engine and warm up the transmission.
Shift into forward and reverse while monitoring the pressure.
Verify the readings:
- Normal operating pressure: 250-400 psi
- If pressure is too low, check for fluid leaks, clogged filters, or a failing pump.

45. How can I improve performance under heavy loads?

To optimize the Twin Disc MG518 Marine Gear under heavy loads:

Use high-quality transmission oil that meets Twin Disc specifications.
Ensure proper cooling by regularly cleaning the oil cooler.
Avoid excessive throttle changes, which can wear down clutch plates.
Regularly check for signs of slippage, misalignment, or overheating.
Use premium aftermarket parts from Diesel Pro Power for longer durability.

46. Where can I find technical support for the MG518?

For expert assistance with troubleshooting, maintenance, or parts replacement for the Twin Disc MG518, you can:

Visit Diesel Pro Power’s website (https://dieselpro.com) for technical resources.
Contact Twin Disc customer support for OEM guidance.
Consult marine transmission specialists or local repair shops.
Refer to the Twin Disc MG518 Service Manual for detailed specifications.

47. What are the warning signs of clutch pack wear?

A worn clutch pack will show the following symptoms:

Slipping under load – Engine RPM increases without speed increase.
Delayed engagement – Slow response when shifting into gear.
Burnt oil smell – Indicates excessive heat due to friction.
Metallic debris in oil – Worn friction material entering the fluid.

If these symptoms appear, replace the clutch pack immediately to prevent further damage.

48. What’s the best way to prevent corrosion on the MG518?

To protect the Twin Disc MG518 Marine Gear from corrosion:

Use marine-grade lubricants that contain anti-corrosion additives.
Inspect and replace seals regularly to prevent water intrusion.
Store the transmission in a dry, climate-controlled environment when not in use.
Apply a corrosion inhibitor on external metal surfaces.
Clean the oil cooler and lines to prevent moisture buildup.

49. How do I perform a system flush on the MG518?

Flushing the Twin Disc MG518 is necessary when fluid contamination or sludge buildup occurs.

Procedure for Flushing the Transmission System:

Drain the old transmission fluid completely.
Refill with a flushing fluid or lightweight transmission oil.
Run the engine at idle for 10-15 minutes while shifting between gears.
Drain the flush fluid and inspect for debris or contaminants.
Replace the filter and refill with clean transmission oil.
Test the system for proper engagement and pressure levels.

50. How do I extend the lifespan of the Twin Disc MG518?

Maximizing the lifespan of the Twin Disc MG518 requires proactive maintenance and high-quality replacement parts. Follow these best practices:

Change the transmission fluid and filter regularly (every 500 hours).
Keep the oil cooler clean and ensure proper heat dissipation.
Use only premium aftermarket parts from Diesel Pro Power to maintain performance.
Avoid excessive shifting at high RPMs to reduce clutch wear.
Monitor for early warning signs such as vibrations, overheating, or slow engagement.

By following these steps, you can ensure that the Twin Disc MG518 Marine Gear operates efficiently and reliably for years to come.

Please follow and like us:

Success!

Home | Blog | 50 FAQs About The Twin Disc MG518 Marine Gear