Diff Oil ??? EP or not EP ?

[flywheel1935]

ARQ Ruby, Do I EP 140 or not & go for a multigrade diff oil ??? Help !!!!

[Alan Osborne]

I was told by cherished suppliers at the Centenary to use D140, which I believe to be non-EP.

[flywheel1935]

That's what I gathered too, that is, not to go to EP ( Extreme Pressure ???) but needed to check, cheers.

[Colin Morgan]

From previous posts on here, it seems that something like "Millers Classic EP 140 GL4 which states it is ok to use with bronze and brass" is what is required - this is because, from my understanding, the pressures between the pinion and crown wheel teeth for this design do need an EP grade.

[David Stepney]

I use a straight SAE 140 in my rear axle.

[flywheel1935]

British Made SAE 140 Gear Oil - SAE140 Classic Gear Oil Non EP 1L Green Gear,
bought this off fleabay from C Bennis Supplies, see the possible need for an EP oil, but this
seems to fit the bill, maybe EP is better suited to straight cut gears ??? where as a crownwheel and pinion will 'slide' across the tooth surface.

[Colin Morgan]

Spiral bevel gears are best with EP? 

"Hypoid gears have axes that are non-intersecting and not parallel. In other words, the axes of hypoid gears are offset from one another. The basic geometry of the hypoid gear is hyperbolic, rather than having the conical geometry of a spiral bevel gear.

In a hypoid gear, the spiral angle of the pinion is larger than the spiral angle of the gear, so that the pinion diameter can be larger than that of a bevel gear pinion. This offers more contact area and better tooth strength, which means that more torque can be transmitted and high gear ratios (up to 200: 1) can be used. Because hypoid gear shafts do not intersect, bearings can be used on either side of the gear to provide additional rigidity.

The difference in spiral angles between the pinion and the crown (larger gear) causes some sliding along the teeth, but the sliding is smooth, both in the direction of the tooth profile and lengthways. This gives hypoid gears very smooth running properties and quiet operation. However, due to the pressure between the teeth, special EP (Extreme Pressure) gear oil is also required to maintain effective lubrication."

("The main difference between GL-4 and GL-5 gear oils is the amount of EP additives. Sulfur/Phosphorus-containing products are used as EP-additive. This additive has the purpose to prevent the occurrence of micro-welds on the gear flanks at the local high temperatures which prevail in EP circumstances (temperatures well in excess of 800℃!) GL-5 has roughly twice the amount of EP additives compared to GL-4, which is why it is often used in high-pressure circumstances such as in a front axle and rear axle differential.

However, sulfur/phosphorus additives have an unfavorable property: they can react aggressively to bronze and copper. ... Therefore, it is not recommended to use GL-5 ... unless the manufacturer allows it.")

[Tony Griffiths]

As stated, normally, EP oils contain sulphur - in either an active form - that will attack bronze, copper and their alloys - or an inactive, which won't. If an EP oil has an API rating of either GL-4 or GL-5 then the sulphur is inactive and should be safe to use in boxes with bronze bearings. Possibly EP is an over-the-top answer?

[Parazine]

I use a straight SAE 140 in my rear axle.

+1 for the last 45 years, no trouble experienced.

[Graham Barker]

I have been using Penrith Gear Oil Premium Mineral ,(140) - API GL-5/GL-6/MT-1/PG-2.
On the bottle are the words "Compatible with copper alloy components and protects against corrosion".  So do members think that I do not have to worry about corrosion of bronze components in the diff?