Vacuum test problem ?

I'm trying to vacuum test my old Volvo Penta SP-A outdrive which is still on boat. My Workshop manual calls for 50kpa, I'm getting a max reading of 25kpa and holds at this pressure for over an hour. Don S. mentioned in an old thread, that the drive shaft seals only hold a certain pressure and to "tip" drive to enable a more accurate reading ?

Could Don S. or someone help me on this, the drive has water in oil so trying to locate leak. What is an acceptable reading?

Thanks

Re: Vacuum test problem ?

Did you have water in the bellows?

Re: Vacuum test problem ?

Hi Don, thanks for your response - No water in bellows, replaced every other season, dry inside - I had noticed an oil leak around the outdrive whilst boating, pulled boat out.

Outdrive oil shows signs of water, drained oil out of drive - pressure tested - held 15psi for 3 hours, no drop in pressure, rotated prop, shifted gears - still held at 15psi.

Attempted vacuum test, only would hold 25kpa ( my vp workshop manual asks for 50kpa ), tried thick oil around shift seal & prop seal etc, just making a big mess with the oil, no change in vacuum reading.

I have tried to get oil around drive shaft seal, difficult with drive on boat as cannot be certain oil is getting all around seal. Have not been able to prove location of leak so far

Re: Vacuum test problem ?

The drive shaft seal is where it sucks air, that doesn't make it bad, they just aren't designed to hold suction, only pressure. The only way to stop that is to take the drive off, and lay it down on it's back and fill the cavity around that seal with heavy gear lube, then do a vacuum test. Lot of work for a test that probably won't tell you anything.

Re: Vacuum test problem ?

Agreed, as I have no water or oil in bellows I do not suspect the drive shaft seal, I guess I'm looking at shift seal & prop seals as main culprit, hate to replace seals when I can't prove the fault. The pressure test held solid at 15psi, I'm doing all the tests via the drain plug, could be the drain seal that I'm not testing although I do replace this every oil change. How many years do shift & prop seals generally last, I've had this boat 6 years so maybe they are due?

Re: Vacuum test problem ?

What about the drain, fill, dipstick tube gaskets? Where ever you tested the pressure at could be at fault. Those gaskets should never be re-used.

Re: Vacuum test problem ?

Good point, I've only managed to get hold of an adapter that fits my drain plug for doing the pressure / vacuum tests - all tests have been done via this location. Perhaps I need to get hold of an adapter that fits my dipstick and re-do tests - not an easy part to get hold of..

Thanks for your input Don, much appreciated

Re: Vacuum test problem ?

Just a thought, is it possible for older seals to leak when hot under operating conditions and re-seal when cool? So as a possible reason for masking the fault.

Re: Vacuum test problem ?

The dipstick and drain plug are the same size. Since you used the drain plug, and it now doesn't leak when testing, put a new oring on the drain plug and go boating and see if you still get water.

Re: Vacuum test problem ?

My adaptor that I'm using has a long thread so will fit drain plug but will not fit all the way in the dipstick plug.

Thanks Don, good to bounce ideas off you and narrow down to a logical approach. I'll let you know how this works out..

Cheers,