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The chart below shows the areas boat owners have most common questions on when trying to troubleshoot why their Allison marine transmission MH, models MH20, MH20L, MH20R, MH45, MH45L and MH45R 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 Allison 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 Allison marine transmission Allison marine transmission MH,models MH20, MH20L, MH20R, MH45, MH45L and MH45R Owner's operating or service manual. AREA PROBLEM POSSIBLE REASON RECOMMENDED ACTION CHECK POWER A. No power is transmitted when selector is in forward position. B. No power is transmitted when selector is in reverse position. C. No power is transmitted regardless of selector position. OIL PRESSURE D.Low oil pressure regardless of selector position. E.Low oil pressure when selector is in forward position. F.Low oil pressure only when selector valve is in reverse position. DRIVE SHAFT G. Drive shaft rotates with selector valve in neutral after shifting from forward to neutral. H. Drive shaft rotates with selector valve in neutral after shifting from reverse to neutral. CLUTCH I. Forward clutch slipping or slow to engage. J. Reverse clutch slipping or slow to engage. POWERPACK K. Powerpack lacks power and acceleration. TRANSMISSION L. Transmission overheats OIL M. Oil is aerated (foaming) N. Heavy metal debris found in oil O. Coolant is found in oil
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Worn forward clutch facings
Replace clutch plate.
Damaged forward clutch plate
Replace clutch plate.
Improper dump valve operation
Clear dump valve thoroughly and replace damaged parts.
Low oil pressure
Refer to D, E, or F.
Worn reverse clutch facings.
Replace clutch plate.
Damaged reverse clutch plate.
Replace clutch plate.
Damaged planetary assembly
Repair or replace planetary assembly
Low oil pressure
Refer to D, E, or F.
lnternal mechanical failure
Overhaul transmission
Driverline failure
Check input and output of transmission
Low oil level
Restore proper oil level.
Low oil pressure
Refer to D, E, or F.
Manual selector valve not positioned properly.
Check linkage.
Low oil level
Restore oil level.
Improper operation of oil gage
Replace oil gage or, if the oil gage is slow to register, bleed the oil gage line to remove entrapped air or obstruction
Improper oil viscosity
Check the oil temperature and if found to be abnormally high, remove the transmission oil cooler and clean internally and externally. Replace the cooler if necessary.
Improper pump adjustment
Shirn the pump. Refer to engine service manual.
Restrieted or damaged oil lines
Check oil lines.
Broken or worn forward piston sealrings
Replace forward piston sealrings
Leaking pilot bearing oil seal
Remove and replace pilot bearing oil seal
lmproper operation of dump valves
Clean dump valves thoroughly and replace damaged parts
Faulty flywheel.
Replace loose or missing oil passage plugs. Check emergency engagement bolts for tightness. Tighten loose bolts.
Damaged output shaft sealrings
Replace sealrings.
Broken or worn reverse piston sealrings
Replace sealrings
Damaged driveshaft sealrings
Replace sealrings
Sticking forward clutch plate
Replace clutch plate
Damaged forward clutch plate
Replace clutch plate
Damaged forward piston drive pins
Replace damaged drive pins.
Damaged forward piston
Replace piston.
Damaged planetary assembly
Repair or replace planetary assembly.
Improper dump valve operation
Clean dump valve thoroughly and replace damaged parts.
Faulty drive shaft sealrings
Replace sealrings.
Control linkage out of adjustment
Check linkage adjustment
Sticking reverse clutch plate
Replace clutch plate
Damaged reverse clutch plate
Replace clutch plate
Damaged reverse piston drive pins
Replace damaged drive pins.
Damaged reverse piston
Replace piston.
Damaged planetary assembly
Repair or replace planetary assembly.
Control linkage out of adjustment
Check linkage adjustment
Low oil pressure
Refer to B,D or F
Damaged forward piston or clutch plate
Replace piston or clutch plate.
lmproper dump valve operation
Clean dump valve thoroughly and replace damaged parts.
Worn piston sealrings
Replace sealrings.
Low oil temperature
Use recommended oil. Preheat if required.
Worn driveshaft sealrings
Replace sealrings.
Leaking pilot bearing oil seal
Replace oil seal.
Low oil pressure
Refer to D or E.
Damaged reverse piston or clutch plate
Replace piston or clutch plate.
Worn reverse clutch facings
Replace clutch plate
Worn piston sealrings
Replace sealrings
Low oil temperature
Use recommended oil. Preheat if required.
Worn driveshaft, sealrings.
Replace sealrings
Engine malfunction
Refer to engine service manual.
Output shaft (propeller) restricted
Clear away obstruction
Boat not properly propped
Change transmission ratios or re-prop boat
High or low oil level
Restore proper oil level
Aerated (foaming) oil
Refert to M.
Craft overloaded
Reduce load.
Engine coolant overheated
Correct engine overheating.
Cooler or iines kinked or clogged
Clean or replace cooler or line.
Low coolant level
Add coolant, check for leaks
Oil leaking
Correct leaks
Low oil pressure
Refer to D or K.
Clutch slipping
Refer to I or J.
Output shaft (propeller) restricted
Clear away obstruction
Incorrect type oil used
Change oil; use proper type
High or low oil level
Restore proper oil level
Air entering suction side of oil pump
Check oil pump bolts and gasket
Water in oil
Check for source; clean system
Gear baffle not installed
Rebuild reverse components, install baffle.
Transmission internal failure
Completely disassemble, clean, and repair transmission. Replace filters and transmission oil cooler. Clean all external lines.
Cooler leaking
Completely disassemble and thoroughly clean transmission. Replace both foward and reverse clutch plates. Repair or replace cooler. Replace filters. Clean all external lines
