Testing gear case seals

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Oldslowandugly
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Joined: Fri Jan 15, 2016 11:19 pm
Location: Queens NY

Testing gear case seals

Postby Oldslowandugly » Sat Mar 03, 2018 5:20 pm

When you change seals in a gear case you then test the seals with air pressure and vacuum. Should you put in oil and drain it- or test the case dry?

Jefecinco
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Location: Gulf Shores, AL

Re: Testing gear case seals

Postby Jefecinco » Sat Mar 03, 2018 7:36 pm

I've done this on a sterndrive gearcase. It was dry but the pressure was low and soapy water was used on the outside much as we used to use to find a leak in a tire tube. I don't recall the pressure used but I turned my regulator to a very low setting. The manual should give you a recommended pressure.

I did the test dry to avoid a mess if there was a leak, but on pressure vessels we always did a hydrostatic test. We were using much higher pressures and I believe the hydrostatic test was to prevent any damage.

The sterndrive was a Mercruiser Alpha drive.
Butch

BDBinWV
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Joined: Mon Jan 25, 2016 3:57 pm

Re: Testing gear case seals

Postby BDBinWV » Tue Mar 06, 2018 12:20 pm

Outboard lower units are tested dry. The use of soapy water helps tremendously in finding any leaks.
Last edited by BDBinWV on Wed Mar 28, 2018 12:36 pm, edited 1 time in total.

jimh
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Re: Testing gear case seals

Postby jimh » Wed Mar 07, 2018 3:19 pm

Check the service manual from the manufacturer to get the specified positive and negative pressures to be used in testing the gear case seals. As I recall, the pressure is typically low, just a few PSI. The pressure is to be held for ten minutes or so, and checked for leak-down. The gear case has to be empty during the test. If there were fluid in the gear case, when applying a negative pressure the fluid would tend to be sucked into the pressure tester.

Oldslowandugly
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Joined: Fri Jan 15, 2016 11:19 pm
Location: Queens NY

Re: Testing gear case seals

Postby Oldslowandugly » Sat Mar 10, 2018 10:47 am

OK- dry it is. Thanks. I was unsure because It took a lot of pressure to find the leak. I guess the residual oil helped the seal resist leaking. When I drained the oil last Fall I got butterscotch looking gunk. Letting it set in a jar allowed the water to settle out and I knew I had a leak. At first the recommended 15psi pressure did not show anything. I then submerged the entire lower unit in a slop sink and pumped it up to 30 psi. Still no leak even while turning the drive and prop shafts. It was only when I moved the shift shaft that the air bubbles showed. So I replaced the shift shaft seals and I am about to test but I could not remember if it should be dry or wet. Thanks again.