Is there a breather pipe in the Yanmar 336D 4wd front axle?

777funk · Jun 12, 2019

I looked quickly and didn't see one. There should be a breather for when the oil heats and expands in any axle shouldn't there be?

winston1 · Jun 12, 2019

I am not certain but I don't think so.

HoyeTractor · Jun 13, 2019

Ive looked all over that axle before and never could find one. I decided that maybe the plug in the top of the center housing might have a groove in the threads or something like that to keep it from completely sealing. Just my guess though. I would sure think it would need something.

777funk · Jun 13, 2019

Maybe the reason for the leaking knuckle seals... of course everything wears out eventual so maybe not... but pressure buildup can't be good.

4get gto · Jun 13, 2019

I'd go out a limb and say the pressure build up the front 4wd to be very minimal.

rScotty · Jun 13, 2019

777funk said:
Maybe the reason for the leaking knuckle seals... of course everything wears out eventual so maybe not... but pressure buildup can't be good.

Just because the old Yanmars were so good doesn't mean they were perfect. Maybe in a rice paddy there was a reason to seal the axle - but I doubt it. For awhile I thought that the lack of an axle vent was an oversight, because some of the Yanmar front axle castings that I've seen have a cast protrusion right where one would expect either a vent or a dipstick, but the area was never drilled, machined, tapped, and the appropriate part added. So it's maybe an manufacturing oversight....but also the venting in other areas is not as good as one would expect, and the resistance to rainwater is worse too. So it could have just as well been an engineering oversight.

Nothing's perfect, but that's no reason not to improve it.

On our Yanmars I vented the brakes and the rear end properly. I didn't do the front axle, although if I had been using it in the wet I would have. The venting I did stopped the brake drums and parts from rusting, and extending the rear end vent with a simple longer tube kept rain water from getting into the rear end.

There is absolutely no mechanical reason that the front axle should not have a vent, and some reasons why it should. It's easy enough to add such a vent....but it then becomes one more thing to check to make sure it is working properly. Maybe that's why they didn't do it.... or maybe it's just because even they never expected their tractors to last so long or to become such icons.
rScotty

777funk · Jun 13, 2019

Well I did an experiment today and as the knuckle was leaking, I unscrewed the fill cap. It didn't slow the leak at all. But... the pressure build up may have blown the seal (o-ring I had added) out of it's place. Hard to say. I'll be fixing it more permanently soon. I may also add a vent.

rScotty · Jun 13, 2019

777funk said:
Well I did an experiment today and as the knuckle was leaking, I unscrewed the fill cap. It didn't slow the leak at all. But... the pressure build up may have blown the seal (o-ring I had added) out of it's place. Hard to say. I'll be fixing it more permanently soon. I may also add a vent.

A vent wouldn't hurt.
I wonder just how much pressure can be built up in that axle? Off the top of my head I just don't think there is much pressure available in that axle. My guess - and it's strictly a guess - is that any pressure in there is due to temperature and that there isn't enough internal positive pressure to move that O ring seal of yours. I may eventually get around to doing some some rough pressure calculations unless someone else beats me to it.
rScotty