Lower unit pressure/vacuum test question

[Moody Blue]

1971 Merc 800.

Had my lower unit completely apart last summer to replace the driveshaft, shift cam and cam follower, clutch dog and reverse gear. Replaced ALL the seals and used thread sealant on the carrier nut threads. After running the motor for about 12 hours I discovered about 1/4 cup of water in the gearcase. Drained everything, refilled and ran it another 10-12 hours with the same results. Never bothered finding the cause, just kept refilling throughout the season.

Now it's time to fix the problem. I want to pressure test and vacuum test the unit to find the cause of the leak rather than just start throwing seals at it again. The pressure test is very obvious to me but the vacuum test has me puzzled. If I apply a vacuum to the lower unit, how will I know if/where the leak is? I obviously can't see inside the gearcase What am I missing?

 

[Moody Blue]

Re: Lower unit pressure/vacuum test question

Bump

 

[Moody Blue]

Re: Lower unit pressure/vacuum test question

No takers? Where are all the Merc tech's ?

 

[cr2k]

Re: Lower unit pressure/vacuum test question

A vac test will tell you there is a leak. you may be able to set the seal where you can spray some fluid on it and it will stay unless it is being sucked in.

 

[Marine Mechanic]

Re: Lower unit pressure/vacuum test question

Spray the seals with a fluid. One question did you replace the seals in the water pump base? If it hold pressure and a vac test the water pump base is usually the culperate. I would just buy a new base with the seals already installed.