Recommended Oils

[SteveM]

I'm going to change the oils in the 4 speed gearbox and diff in my 73 cs and am looking for recommendations from fellow owners. My search of the site bought up little but a confusing set of opinions on hypoid/non-hypoid or GL4,5 and 6 oils - a least confusing to this reader...
I'm in Australia so any suggestions from locals would be great as I don't think some of the oils used in the US & Europe are available here.

 

[MMercury]

I'm going to change the oils in the 4 speed gearbox and diff in my 73 cs and am looking for recommendations from fellow owners. My search of the site bought up little but a confusing set of opinions on hypoid/non-hypoid or GL4,5 and 6 oils - a least confusing to this reader...
I'm in Australia so any suggestions from locals would be great as I don't think some of the oils used in the US & Europe are available here.

In the decades since the design and manufacture of E9 transmissions, newer lubricants have appeared on the market as have different transmission designs. While some oils seem to be backward compatible and improvements, so that they can be used with older equipment, this is not the case with the manual transmissions originally installed in E9's and other Bmw models of that era.

First, when in doubt, try the owners manual which clearly specifies: "Branded SAE 80 gearbox oil [GL4](not hypoid gear oil). . . ." (See below - last paragraph, second column)

Rereading this thread [ http://www.e9coupe.com/forum/showthread.php?t=4518 ] suggests continuing confusion regarding the use of the label "hypoid." Percy spells everything out. Hypoid can refer to an actual gear design (spiral cut as found in: worm gears or ring and pinion gears and usually NOT straight cut manual transmission gears). Hypoid gears, by their inherent design, can benefit from a lubricant that can handle extreme pressures, hence the EP designation.

To recap: typical hypoid lubricants [GL5] are laden with sulfur-based extreme pressure additives. These additives tend to have a corrosive effect upon the brass/bronze (yellow metal) components (synchronizers) used in your 4-speed. GL5 hypoid lube is generally reserved for steering boxes and differentials - as these components do not ordinarily contain brass/bronze/yellow internals. Some manual transmission may use non-yellow metal components that are not affected by the GL5 additives. Unfortunately, unless your Getrag or ZF 4-speed transmission has been reengineered, redesigned or remanufactured, it contains the yellow metal that is vulnerable to these additives.

Regardless of the reasoning behind its language choice, BMW's manual obviously distinguishes between certain generic grades: hypoid versus not hypoid. In more modern parlance, GL4 can be considered not/non hypoid with GL5/6 being deemed hypoid. To be crystal clear, it is API grade GL5/6's potentially caustic effect on your synchros that you wish to avoid.

For your present conundrum, stick with the GL4 designation only (and not something akin to: "meets or exceeds GL4, GL5 or GL6"). An obvious exception to this rule might be where the later-formulated lubricant has been designed so that it is not harmful to yellow metal, as might be found in some newer formulated synthetics.)

I can't speak intelligently about what is currently available down under, but there must be several products bearing a GL-4 rating or some kind of claim re "excellent yellow metal compatibility." By way of a quick example, search for Pennzoil synchromesh manual transmission lube and Valvoline Duragear 75W/85.

hth

http://www.britishsportscars.nl/Castrol Classic Oils.htm

http://www.mbfanatics.org/forum/index.php?showtopic=3352

http://www.lubeandtune.com.au/html/lubekey.asp

 

[SteveM]

Thanks

Thank you for this informative and clear-cut reply - you're not a barrister are you?
Cheers