Vacuum check outdrive

[gimmieaclue]

Bought a used pre alpha outdrive to replace the one on my boat. Pressure checked it and it held 15lbs for a half hour or so but when I went to measure vacuum it keeps bleeding down to about 4 and holding. I don't know a lot about what I'm doin, just what I've read on here. I read somewhere that I was looking for about 8 and that it wouldn't hold more than that. Should I be concerned that its holding less than 8?

 

[Fordiesel69]

Re: Vacuum check outdrive

Pressure check over night and look for oil leaks or bleed down on the guage. If all is well, skip the vacuum check.

 

[Failproof]

Re: Vacuum check outdrive

I think the vaccuum check is important. verifies that you wont be sucking water in as the drive unit cools after operation. It should hold pressure for a while, and vaccuum just as long.

 

[gimmieaclue]

Re: Vacuum check outdrive

I thought it was important also......from what I understood the pressure check confirms the seals holding the oil in are good and the vacuum checks that the seals keeping the water out are fine, just not sure whats an acceptable range for the vacuum.

 

[Fordiesel69]

Re: Vacuum check outdrive

When a drive is hot, it will push lube out the seals and when it coold, will draw water in those same faulty seals. If they are not leaking outwards, they will not be leaking inwards.

 

[Don S]

Re: Vacuum check outdrive

To PROPERLY pressure test an outdrive, you drain all the gear lube, then you pressureize the drive to 12 to 15 psi, turn the shafts, and the shifter while spraying soapy water on all the seals. If that doesn't find the leak, put the drive in a tub of water and look for bubbles.
The vacuum test seldom shows a leak, the input shaft seal will not hold vacuum. If it will holds 4 inches of vacuum, it should be good to go.

 

[achris]

Re: Vacuum check outdrive

The other place that like to 'leak vacuum' is the lower shift shaft seal, in the lower gearbox....

Chris..........

 

[Fordiesel69]

Re: Vacuum check outdrive

I will add, we had a drive not leak when it was full of oil, as Don stated, once the fluid was drained, the prop shaft began leaking.

 

[gimmieaclue]

Re: Vacuum check outdrive

thanks for the responses. I did drain the oil before I did the pressure/vacuum checks and also turned the shafts while checking, there was no leak down while under pressure.........I'm glad to hear that 4 in was an acceptable amount of vacuum.........thanks again