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GL5 oil

GL5 oil

GL5 oil

I recently visited a restoration firm in Germany where I was shown a rea raxle with wormdrive where the bronze main gear was totally worn away.
The restorer told me that after changing to GL5 oil the axle started whining and desintegrated within one hour.
I know that some older EP oils had chemicals that attack bronze bearings but I have never heard that from GL5 oils.
I asked whether they changed from vegetarian oil(e.g;. rinseed) to mineral oil without rinsing the axle but was told this was not the case.
Any aidea?

RE: GL5 oil

Was the rear axle in your car being "restored" ?
Or Are you being "consulted" ?
Is the oil that killed the bronze gear still in a bucket someplace?

I think the GL5 oil never made it into the rear axle after it ( the rear axle) was drained.

RE: GL5 oil

I have long heard the recommendation to use GL4 and not GL5 in any manual transmission due to incompatibility of GL5 with copper alloys.

Minor digging finds that GL5 is meant for use in hypoid rear axles (which have steel gears, rolling-element bearings, and shouldn't contain any bronze bushings), and GL4 (or motor oil, or ATF, or basically anything but GL5) is recommended for manual transmissions (which contain bronze parts).

That worm-drive final gear is a special case.

RE: GL5 oil

Thanks for answers! What I saw was just the remains of the gears,happened some time ago. They are reputed mechanical restorers and the only thing I can think off is that the vegetarian oil that remained coagulated with the new GL5 oil. They do not mix.
The only reason I now for not using GL5 has to do with the synchromeshes not working well( too slippery)
Most worm driven rear axle gears had castor oil in them in the early years.

RE: GL5 oil

Optimal worm gear lubrication is very specialised. An oil that works well with synchronisers is likely to be far from optimal in a worm drive.

je suis charlie

RE: GL5 oil

A worm gear axle has quite different lubrication requirements then an hypoid axle. The EP additives usually found in a API GL5 lubricant have no positive effect on lubrication of the worm gear, but can be quite aggressive towards yellow metals. What you need is a lubricant with far better adhesive qualities - in the past vegetable based lubricants where used for that reason. In worm gears the loading is relatively low but sliding speeds are excessive - and natural ester based lubes do adhere quite a bit better to metals then petroleum based lubes. API previously had a separate designation for worm gear lubricants (API GL3), but that has been discarded years ago and products meeting that classification are very rare nowadays.

A useful alternative would be a modern industrial gear lubricant of suitable viscosity recommended for use in industrial worm gears. Those products contain additives that are not aggressive towards yellow metals and adhere to metals under conditions of extreme sliding quite well.

What kind of axle was destroyed?

RE: GL5 oil

It was a prewar axle,but cannot remember which car. I think Your comment is right! Thanks!

RE: GL5 oil

It has been a long time since I looked it up, but I recall the GL5 spec includes a test for yellow metal compatibility. Lots of things could have been the root cause for the referenced failure, but I don't know why they have such a test in the spec if GL5 oils are fundamentally chemically incompatible with (any and all) bronze gearbox parts, as seems to be conventional wisdom when problems arise.

RE: GL5 oil

GL-5 formulations in the past (say before 1980)were known to affect yellow metals in some cases and therefor GL-5 contains a yellow metal compatibility test. Modern formulations use a variety of EP-additives that are no longer aggressive against yellow metals. API GL-5 is a rather old though not obsolete classification, modern automotive gear lubricants meet quite a bit more requirements then GL-5, such as cold flow properties, air release properties, demulsability, foaming tendency, seal swell and many more. In Europe GL-5 as such is hardly used nowadays - most equipment requires a proprietary specification with far more stringent requirements. In the US API GL-5 has been more or less superseded by API MT-1/SAE J2360 - a lubricant both for driven axles and non-synchromesh gearboxes that also meets much more stringent requirements then API GL-5.

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