Hi,
I hope this helps;
As you are probably aware a modern ATF is simply a semi-synthetic gear oil with added and sometimes very specific formulated qualities
Its prime role is to lubricate the drive gear set - its other roles are "circumstantial" in that they may and do vary according to the nature of the individual components within the transmission. Sometimes they are formulated for a specific transmission or retarder or both and their abilities in heavy trucks is well known - they are robust!
Technical reasons calling for one gear lubricant over another also emanate not only the metallurgy involved but from the type of gear cutting/profile ( noise etc.) and design use/loading factors, bearing size and structure, shock loading requirement, anticipated temperature range in use etc etc.
The GM Dexron type ATFs have been used in manual gearboxes by various manufacturers for about 50+ years. If I remember correctly all MB cars for instance had such requirements from the early 1950s. Volvos even in the 1960s required ATFs and many light and heavy trucks have used them for decades. There is an established history!
The benefits of the ATF ( compared to a gear oil ) are its low pour point and its low viscosities both at 40C and 100C along with its inherent ability to handle very high temperatures. Usually the high VI tells the story too as it can be up to double that of some gear oils
This then enables a "robust" manual gearbox to have excellent very cold ambient gear selection characteristics along with a good shift "feel" at very high temperatures
The overall lower viscosity of the ATF ( compared to a gear oil ) also aids in cooling the components. Its formulation components have other "spin off" effects like anti foaming, seal and component cleanliness along with excellent thermal, shear and oxidation stability. Fully synthetic ATFs are sometimes used as a lifetime fill in manual gearboxes because of their overall stability and long term durability
Today's choice of gear lubricants is truly amazing. They range at least from a mono HD10w thru engine oils ( mineral/synthetic - mono/multi grade) to the GL API classified lubricants and the various ATF types available
It is wise to use only what gear/transmission lubricant the manufacturer calls for. If an ATF is called for, a fully synthetic version may also be suitable - if so it will normally make a difference by reducing component operating temperatures and provide improved shift quality
Regards
Doug
MY02 Subaru Outback 2.5 man.(Del 1,D/T all syn)
MY98 BMW Z3 2.8 man.(Del 1,Gbox synATF,syn Diff)
MY89 Porsche 928S4 Auto(Del 1,Gbox synATF,syn Diff)
