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Helpful Tips

Helpful Tips

Troubleshooting Checklist for Twin Disc MG506 Marine Transmission

The chart below shows the areas boat owners have most common questions on when trying to troubleshoot why their Twin Disc ® marine transmission MG506 underperform.  It categorizes areas of possible malfunction, likely cause and recommended action to bring your new, rebuilt or used  Twin Disc ® marine transmission back to proper operation.  The chart will give you confidence when speaking with your Twin Disc ® marine transmission mechanic or ordering parts.  As a quick reference guide only, the chart must not be thought of as a substitute for the use of your Twin Disc ® marine transmission MG506 Owner's operating or service manual
For convenience in looking up parts and pricing for your marine transmission please click here. You can also call us at 1-888-433-4735.
Print out our checklist and post it in your boat engine room or Marine work station.

AREA

PROBLEM

POSSIBLE REASON

RECOMMENDED ACTION

 CHECK

OIL PRESSURE

Low oil pressure

Partially clogged filter screen Remove and clean filter screen  
Stuck main regulator valve. Remove main regulator valve parts from valve body, and clean parts.  
Broken or worn piston rings on clutch shafts Remove pump mount and selector valve assembly from rear cover. Remove piston rings from clutch shafts. Install new piston rings on clutch shafts.  
Damaged or worn oil pump assembly. Remove and replace the oil pump assembly.  
Damaged or worn clutch piston, piston rings Remove marine gear. Disassemble clutches, and replace damaged or worn parts.  
Scored valve bore in selector valve assembly.  Remove selector valve assembly. Disassemble selector valve assembly and inspect valve bore.  
Reverse clutch housing gear turning on shaft.  Remove and replace the oil pump assembly.  
 

No oil pressure

Low oil level or empty sump. Check gaskets and seals for leakage. Replace parts causing leakage, and fill marine gear sump.  
Fully clogged filter screen.  Remove and clean filter screen.  
Damaged suction tube.  Disassemble and inspect suction tube. Replace parts as required.  
Damaged or worn oil pump assembly. Remove and replace oil pump assembly  
Broken clutch shaft Remove marine transmission. Dissemble clutches, and replace damaged or worn parts.  

High main oil pressure

Stuck main regulator piston. Remove main regulator valve parts from valve body and clean parts.  

Overheating

Insufficient heat exchanger capacity. Find a heat exchanger of sufficient capacity and replace it.  
Insufficient cooling water flow. Replace lines and/or hoses with larger inside diameter lines and/ or hoses.  
Clutches Slipping. Low oil pressure, removes marine transmission, disassemble, and inspect for worn clutch plates.  
Oil levels too high Correct oil level.  
Improper oil sump. Drain marine gear, and fill with proper oil.  
Clutch piston springs broken. Remove marine transmissions dissemble clutches and replace damaged or worn parts.  
Clutch plates warped Replace clutch plates Remove marine transmissions dissemble clutches and replace damaged or worn parts  
Improper bearing adjustment with shims (especially after overhaul) Check end play of shafts, and make proper shim adjustments.  

Excessive noise

Air leak in suction side of system.  Tighten all fittings and or replace a damages hose.  
Worn gear teeth or splines on marine transmission parts.  Overhaul marine transmission and replace worn parts.  
Bearing failure.  Overhaul marine transmission. Replace damaged parts.  
Worn or damaged rubber blocks.  Remove marine transmission and replace worn or damaged rubber blocks.  
Excessive bearing end play. Check and reset and play.  

No neutral

Clutch plates warped.   Remove marine transmissions dissemble clutches and replace damaged or worn parts.  
Clutch piston spring broken and jammed. Remove marine transmissions dissemble clutches and replace damaged or worn parts.  
Selector valve linkage incorrect. Check linkage and adjust.  
Scored bore in valve body of selector valve assembly.  Remove selector valve assembly. Disassemble selector valve assembly and inspect valve bore.  

Harsh engagement

Air in oil.  Correct air leaks in suction side of system. Change oil to proper type.  
Binding clutch piston. Remove marine transmissions dissemble clutches and replace damaged or worn parts.  

No pressure and No output power

Input shaft broken. Overhaul marine gear. Replace broken or damaged parts.  
Drive spider broken. Overhaul marine gear. Replace broken or damaged parts.  
Drive spider or input gear keys sheared. Overhaul marine gear. Replace broken or damaged parts.  


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