RTA 12 Series Tiller--Breather Plug

[Broomtown]

My tiller has <20 hours service. On last use, a small amount of gear oil seeped out around the top (breather) plug. Would someone explain the exact function of the breather plug and offer ideas as to why it would allow leakage? The threads for breather plug are very tight. Almost like it was a poor threading job when it was built. I was able, using more force than should have been needed, to tighten the plug deeper.
I have also decided to replace the gear oil. No particular reason other than I want to use a synthetic (Schaeffers 75w90). Manufacturer recommends 80w90. Will the synthetic 75w90 be OK for this gearbox application?
I read this forum often and it's helped me a lot. Decided to officially join. Waiting for the expert advice now. Thanks.

 

[Dave_eng]

The tiller manufacturer says more about the gearbox oil than 80W-90.

There are two other letters which are critically important EP.

The EP stands for Extreme Pressure and is achieved using special additives in the oil. It used to be a sulfur compound but likely has changed over time.

Whatever oil you decide to use must have the EP properties.

Any oil will expand and off gas as its temperature increases. This is why vents are incorporated into the design of gear boxes. Otherwise, the buildup of pressure will force oil by the seals.

You should expect to see traces of lubricant escaping from the vent.

Often vent plugs incorporate a sintered bronze element in the plug which allows vapor to escape while keeping out moisture and dirt.

A sintered plug looks like crystals of brass stuck together.

Schaeffer's claims: Excellent extreme pressure properties to protect the gears and bearings from excessive wear and fatigue

Dave

 

[GeoHorn]

There are two major types of gear oils: AW and EP

AW stands for anti wear and usually involves the use of zinc-phosphates.

EP stands for extreme pressure and usually involves sulfur-phospates.

The difference is how the additives actually do their work. The AW types use a coating process that can withstand temperture extremes while the EP operates in a narrower temperature range but requires heat in the region of about 90-C But not much higher.

The two are not interchangeable, so its important to follow the implement mfrs recommendations.

 

[Broomtown]

Thanks for the replies. OK, makes more sense to me now about the breather plug. The breather plug in my gearbox does not have a brass element (sintered). It just has a small hole through one of the hex surfaces. Sounds like it’s doing its job as designed with the small leakage amount. But this was the first time I noticed a leak and that was the reason for my concern. I did tighten the breather plug so that the vent hole will now be facing downward. Seemed like the right thing to do. I’ve had my equipment going on 3 years now but I don’t put a lot of hours on implements or tractor. So I’m really still a rookie to owning this fascinating equipment.
As for the gear oil…I researched the spec sheet PDF on Schaeffer site. I can’t post links yet but see excerpt from their 3 page document……
Shaeffer 75w-90 Synthetic:

1. Enhanced thermal and oxidative stability and durability to handle operating temperatures of 300***61616;F to 350***61616;F.
2. Excellent extreme pressure properties to protect the gears and bearings from excessive wear and fatigue.
3. Prevention of the formation of sludge and carbon deposits that erode the seals.
4. Excellent seal compatibility.
5. Enhanced protection of copper, brass and bronze components from corrosion.
6. Non-corrosivity to brass, bronze and other non-ferrous metal parts.
7. Excellent protection of components from rust and corrosion in dry conditions and in the presence of moisture.
8. Excellent resistance to water and moisture.
9. Excellent water separability characteristics.
10. Enhanced gear, bearing and seal cleanliness
11. Excellent resistance to foaming.

As already pointed out by Dave it says excellent EP properties. So I guess that box is checked?
I had bought a quart of gear oil a while back from my Kubota dealer and told them my exact application. They also looked up my tiller in the system. They gave me Service Pro 80w 90 gear oil API GL-5. Not sure what those ending digits mean. The Service Pro bottle does not state AW nor EP. But I did get this from their spec sheet…..

SERVICE PRO® Premium GL-5 Gear Oils are compounded with highly refined base stocks and additives to ensure extreme pressure characteristics, anti-wear, corrosion inhibition, rust preventions, low pour point, and anti-foaming performance. They are fully formulated for limited slip differentials.

As far as the EP and meeting all the same vehicle/military specs, the products appear to have the same capabilities. However, both talk about EP & AW or protection from excessive wear. So I’m still a bit confused as to the EP vs AW. Thanks for the input.