Originally Posted By: zeng
Whilst most OEMs recommends GL4 in their manual transmissions, the fact remains there are OEMs (though may be of minority) recommending GL5 in their respective manual transmissions.
GL4 came into market well before GL5 with a gap of at least a decade if I may speculate.GL4 could have 'monopolised' manual transmission lubricants market, but fact remains it's not...
The majority of MTF's for cars and light trucks on the market today use the GL-4 protection rated fluids ranging in viscosities from 6.0 to 14.5 cSt@100C.
Manf. specifying GL-5 MTF's is Subaru and a few other manf. in which the differential and transmission share a common sump, and the differential is a hypoid type design. However, this special GL-5 still has friction modifiers for the synchro unit.
Secondly, in terms of volume, the HD and Over-the-Road non-synchronized transmission market uses the GL-5 hypoid-type lube that is also MT1 rated, but this lubricant is formulated much different than the Subaru GL-5 rated "common sump" oil.
When one discusses MTF's, one has to delineate between the various applications.
Otherwise, I still do not see what point you are trying to make.