Pressure test vs vacuum test F150TXRD

[pstephens46]

I see the SM info for pressure testing lower unit casing. Nothing on vacuum testing. Wouldn't it make sense to do both?

[boscoe99]

Not necessarily.

Yamaha perceives the greater risk to be water getting into the gear case as opposed to some gear oil leaking out. Thus, both seals are oriented in the direction so as to keep water out.

I suspect that if a pressure check is good showing that the seals will not allow gear oil out then there is a greater likelihood that the seals will do the job of preventing water from getting in.

However, there is nothing stopping you from doing a vacuum check. What value will you use as your acceptance criterion? 1' Hg, 5" Hg or ...

[pstephens46]

No idea. All I see is 10lbs for pressure test. I don't know enough about these seals to determine a vacuum limit. Mechanic in our truck shop asked if I was testing both ways as if he assumed it was normal protocol.

[boscoe99]

It is normal for some motor makers to test their lower units with both positive pressure and negative pressure. Not so with Yamaha. Some Mercury's only specify positive pressure.

Different strokes for different folks.

[pstephens46]

I'll be content with the 10 psi as specified.

[walleye1]

I think 14.5 psi for mercury, not sure.
If it holds 10 psi for 10 min you will be good.

[pstephens46]

10 minutes or 10 seconds?

[walleye1]

I like seeing it hold 14 over night myself.

[pstephens46]

That would be good

[TownsendsFJR1300]

When the MM resealed the top two seals (under the WP on my F150) a couple of years ago, I watched.

He pressure tested it while rotating the prop/drive shaft while spraying soapy water on it looking for bubbles..

No bubbles and the pressure never dropped. Good to go!!

[pstephens46]

Replaced propshaft, driveshaft and shifter seals. 12 years old. No broken springs or obvious leaks. I found some water on top of second driveshaft seal. I didn't rotate prop while pressure testing. Monday may be warm enough to run the sht out of it. Drain and double check. Hell, it's a hobby, right?

[TownsendsFJR1300]

Replaced propshaft, driveshaft and shifter seals. 12 years old. No broken springs or obvious leaks. I found some water on top of second driveshaft seal. I didn't rotate prop while pressure testing. Monday may be warm enough to run the sht out of it. Drain and double check. Hell, it's a hobby, right?

Per the shop I went to, that seal upper driveshaft seal (that yours held water) should be replaced after several years, period.

That TOP seal on mine, the tension spring (that wraps around it) had failed. #2 seal under it was fine, no water intrusion but replaced both seals.

I inquired as I flush and tilt to get as much water out when done as possible.
They said it doesn't matter, that seal (I gather with the water you found sitting there) fails. Being under the WP plate, perhaps the water never escapes and gets to the seal spring....