Outdrive -- Pressure and Vac tests

[zul]

My mechanic has installed 3 new seals into my outdrive upper last week.
The drive passes an air pressure test.
Vacuum test will not hold air.

Any ideas? It could be my old vacuum tool ... ?

 

[Scott Danforth]

only volvo recommends a vacuum test. I dont recall mercruiser needing a vacuum test.

however regarding your vacuum tool, easy enough to test the tool.

 

[harringtondav]

I wasn't aware of the pressure test nor tool until I signed up for this forum this past May. Since I own a vacuum tester, I've always checked my seal jobs with it over 22 yrs.. I tape over the lube passage in the prop shaft hsg. and always pull 25-26 inches which holds from 1 hr. to overnight.

Then I do the same with the drive shaft hsg. The drive yoke seal is a single seal with the lips/garter spring facing the inside. All other oil seals are double back-to-back seals. My tool will normally draw to only around 9-15 1nches. I can hear the yoke seal hissing, letting air in. The seals hold the oil in when the drive heats up and pressurizes, and keeps the water out when the drive cools and draws a slight negative pressure.......except for the drive yoke seal.

I believe the yoke seal is part of the earlier 'dip stick' models, where the cool down negative pressure relieved itself by pulling air in thru the drive shaft bellows vs. water through another seal. The check valve in the lube monitor models provides the air entry into the system during drive cooling to replace any gear lube that oozed out other seals. That is why Merc. instructs us to keep the bottle's cap tight.

I'm going to the Stickies and get a pressure tester before my next annual - biannual outdrive pull. I always test it to see how the seals are holding up. But I'll still vac. test, out of habit, and to very the water side seals are still doing their job.

.....can't understand why Merc hasn't adopted back-to-back seals on the drive yoke, and ensure all air intake is thru the lube bottle.

 

[achris]

The lower shift shaft seal is also a single. A fully resealed drive should be able to hold about 12" vacuum. Once that seal gets a bit old it usually lets go at about 6". All the rest should hold 12"... And yes, a vacuum test is something I perform and strongly recommend.

I guess the reason the front seal isn't a double is because the should only ever be air in front of it... :noidea:

Chris....

 

[harringtondav]

The lower shift shaft seal is also a single.

Oops, I missed that one. My apologies to my Sensie achris . I'm guessing Merc single sealed that shaft because of it's low rotational speed compared to the other power delivering shafts. Plus it travels w/in <1/4 rev. I did change this seal last Spring, but have to admit I've farted it off before because the used seal never degraded the vacuum, and it's a PIA to pry out, and I didn't want to unnecessarily damage the seal bore. And I am gratified to hear 12" is a good test on a complete drive.

Anyway, another one in the learning list. This forum has provided plenty.

 

[achris]

.... I did change this seal last Spring, .... and it's a PIA to pry out, and I didn't want to unnecessarily damage the seal bore. ...

Usually easier to just unscrew the complete carrier and replace as an assembly.. The cost difference is negligible, and the carrier comes with the seal pre-installed... Just unscrew the old one, toss it in the trash, put a new 'O' ring on the new one and screw it in..

Chris......