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The chart below shows the areas boat owners have most common questions on when trying to troubleshoot why their Twin Disc Ā® marine transmission MG509 underperform. Ā It categorizes areas of possible malfunction, likely cause and recommended action to bring your new, rebuilt or usedĀ  Twin Disc marine transmission back to proper operation. Ā The chart will give you confidence when speaking with your Twin Disc Ā® marine transmission mechanic or ordering parts. Ā As a quick reference guide only, the chart must not be thought of as a substitute for the use of your Twin Disc Ā® marine transmission MG509 Owner's operating or service manual.

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AREA

PROBLEM

POSSIBLE REASON

RECOMMENDED ACTION

CHECK

OIL PRESSURE

Ā Low oil pressure

 Partially clogged oil strainer Remove and clean.

āˆš
Stuck pressure regulation piston in selector valve assembly Remove selector valve assembly. Disassemble the valve and clean piston. Ā 
Broken piston rings on clutches Remove the manifold and dissemble the clutches. Replace piston rings. Ā 
Come-home setscrew loose or missing Remove the some-home access pipe plugs. Tighten a loose come-home setscrew by turning counterclockwise, or replace setscrew. Ā 
Damaged or worn oil pump assembly. Remove and replace oil pump . Ā 
Incorrect linkage installed on selector valve assembly Adjust linkage so that selector valve stem is indexed properly by detent. Ā 
Clogged or plugged orifice in orifice plate of selector valve assembly Remove orifice plate cover. Clean parts. Ā 
Ā 

No oil pressure,
or erratic low pressure
at control valve tap

 Low oil level or empty sump. Check gaskets and seals for leakage. Replace parts causing leakage Fill marine gear. Ā 
Fully clogged oil strainer Remove and clean oil strainer. Ā 
Damaged or worn oil pump assembly. Remove and replace oil pump . Ā 

High main oil pressure

 Stuck pressure regulation piston in selector valve assembly. Remove selector valve assembly. Disassemble the valve and clean piston. Ā 

Overheating

 Insufficient heat exchanger capacity. Find a heat exchanger of sufficient capacity and replace it. Ā 
Insufficient cooling water flow. Inside diameter of water lines too small. Replace lines with larger inside diameter hoses. Ā 
Clutches Slipping. Low oil pressure will cause a clutch to slip. Adjust clutch. Ā 
Oil levels too high Correct oil level. Ā 
Improper oil sump. Drain marine gear, and fill with proper oil. Ā 
Trolling at too high engine speed. Ā  Ā 
Clutch plates warped Replace Clutch plates . Ā 

Excessive noise

 Worn splines between reverse driving and driven gears and clutch shafts Remove marine gear, dissemble marine gear, and replace worn splined parts. Ā 
Bearing failure Remove marine gear. Dissemble marine gear and replace damaged or worn partsĀ  Ā 
Worn or damaged rubber blocks Remove marine gear and replace worn or damaged rubber blocksĀ  Ā 

No neutral

 Clutch plates warped Replace Clutch plates. Ā 

Harsh engagement

 Steel ball in selector valve not seating properly. Remove orifice plate cover clean parts. Replace parts if necessary . Ā 

CLUTCH

Clutch slips

 Improper adjustment Adjust Clutch. Ā 

Clutch will not remain engaged

 Clutch adjustment too tight Adjust Clutch. Ā 
Improper remote engaging linkage. Adjust linkage as required to assure proper travel of operating lever. Engaging force must be removed after complete engagement of the clutch. Ā 

Power Take-off continues to drive when clutch is desengaged

 Warped or welded clutch plates Remove power take-off and replace clutch plates . Ā 
Bearing failure Remove power take-off and replace clutch plates . Ā 
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