GL4 & GL5 Gear Oils - Caution

[Bob Bidonde]

I have been using GL5 70W140 Gear Oil in the transmissions and rear axles of my stock Model A's for many years without any negative effects. However, the amount of extreme pressure additive in GL5 gear oils will attack the yellow metal / copper synchronizers in transmissions, so GL5 is not suitable for the Mitchell Model A transmission with synchronized gears, and it is unsuitable for 1932 & on Ford transmissions.

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[Werner]

Guten Morgen Bob,

what you write must be differentiated a liitle bit still somewhat.


GL 5 is a gear oil that is used for high tooth flank pressures, as they occur with hypoid gearing. For this purpose, sulfur additives were added in the past.

Sulfur attacks "yellow" non-ferrous metal alloys (brass, copper, bronze).

In the meantime, however, sulfur is no longer permitted, or hardly permitted at all, because of environmental protection.

Therefore, another synthetic additive is now added to these high-pressure oils. Then GL 5 is also harmless for yellow metal. This is also indicated on the label of the oil canister.

[Terry, NJ]

Wie Gehts Werner,
Just to expand a little on what you said, Old farmers in the USA were told NOT TO use any lube higher than GL1 in their old tractors because of just as you said, the sulphur would attack the yellow metals. When I was restoring my Ford 8N, I was constantly hearing it, "You must use only GL1, no sulphur!"
Terry

[Ruth]

Mitchell recommends in their O/D instructions to use "A high quality 85/140 weight petroleum based gear oil with a GL5 rating". What are the O/D synchros made of? What is their recommendation for the transmission?

I use Lucas 85/140 in my transmission, Mitchell and rear end. Makes it easier to have one oil for all three. As far as I know, all Lucas gear oils are rated GL4/GL5.

[katy]

Originally Posted by Bob Bidonde

the amount of extreme pressure additive in GL5 gear oils will attack the yellow metal / copper synchronizers in transmissions,

So, how long does it take to do irreplaceable damage?

[rotorwrench]

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The transmissions with the most to lose due to extreme pressure additives are those that have phosphor bronze bushings and thrust washers. The Model A doesn't use synchronizers with the brass blocker rings but later Fords do. There still may be a bushing or thrust washer but the gears are straight cut so thrust loads aren't like the later transmissions with helical cut gears. If Mitchel calls out GL5 then it can be used.

Modern GL5 still uses phosphoric and zinc compounds as well as surfuric and chlorinated compounds but the sulfuric is a less active variant than the more acidic type. It still can get active with higher heat so that's what they use. They don't tell folks much about this stuff but a person still has to be careful what they use. Overdrive transmissions with an overrunning clutch need to stick with something less than GL5 and I still wouldn't recommend it in the old semi synchronous Ford V8 transmissions. The thrust washers and the 2nd gear bushing on them get hot enough to activate the EP compounds in GL5. The rear axles can use it with no problems but they aren't hypoid gears so it's kind of overkill.

[ursus]

The early Model A transmissions had bronze thrust washers at each end of the cluster gear and a lot of them are still out there and running with whatever oil folks choose to use.

[Werner]

Originally Posted by katy

So, how long does it take to do irreplaceable damage?

Ken (remember right?),


this already happens within a less few of years on the synchronizer rings in contact with gear oils containing high levels of sulfur.

The brass surfaces will become microscopically rough surface and therefore they wear more. This is not about the coarse teeth, but about the very fine radial grooves inside on their conical seating surface.

Overall, the low RPM and torque loads on the A gears are very, very low. I am sure that a GL 3 or 4 will not reach its limits, or conversely that a GL 5 will actually allow less wear or a longer lifetime.