Originally Posted By: supercity
I also use VMX-M in my car where the spec is 80w GL-4. I find there are good and bad days. Some days its like silk, others the first shift into 2nd just doesn't want to go.Just curious, what would you refer to as a genuine GL-4?
One gets a good shift feeling in a manual transmission whenever the ratio of static COF to kinetic/dynamic COF is closer to 1 or thereabout.
At a ratio exceeding,say 1.8 and higher, one could be irritated by the 'rough' shift phenomenon.
However, in real life ...................
a smooth and consistent gear shiftability are
elusive often times, as system parameters are continuously changing, whilst in intended operation, throughout the life of a particular lubricant and transmission hardware.
.....The
bold in the wikipedia.org quotes below indicates some of those system parameters.......
Quote:
The coefficient of friction is an
empirical measurement –it has to be measured experimentally, and cannot be found through calculations.[citation needed]
Rougher surfaces tend to have higher effective values.
Both static and kinetic coefficients of friction depend on the
pair of surfaces in contact; for a given pair of surfaces, the coefficient of static friction is usually larger than that of kinetic friction; in some sets the two coefficients are equal, such as teflon-on-teflon.
Quote:
While it is often stated that the COF is a "material property," it is better categorized as a
"system property." Unlike true material properties (such as conductivity, dielectric constant, yield strength),
the COF for any two materials depends on system variables like temperature, velocity, atmosphere and also what are now popularly described as aging and deaging times; as well as on geometric properties of the interface between the materials.
.......... and operating viscosities.... possibly base oil stocks etc of lubricants in question.
Originally Posted By: Shannow
There's been rumour that a "formulated" GL-4, rather than a half treat rate GL-5 is "better"...I dunno.
"better" ...... in the context of smooth gear shiftability .Period.
Gear lubricants are more than shiftability.
In the now obsolete GL4 specification,synchronizer materials and material property in the likes of coefficients of friction (be it static, kinetic or its ratio) were NEVER part of the requirements in SAE GL4 specifications , neither were smooth shift property a requirement.
"formulated" GL-4 ???.....
"dedicated" GL-4 ??? ...... what?
There are non-manual trans oils like differential GL5 oils, CD/Sx engine oils,powershift transmission Cat TDTO/ Allison C4 oils, axle oils etc that, according to the relevant manufacturers/blenders, contains appropriate friction modifier additives for synchronizers to achieve desired static and kinetic coefficients of friction (and desired ratios),among other appropriate additive package, and claims to meet or exceed GL4 requirements.
JMHO.