'Gear Oil Bunk'
The constant reference to 'gear oil' with the MTX75 is
a myth.The first consideration of what type of lube a
trans/gears need is dependant firstly on one thing,the
gear 'cut'.That is the type and angle the gear teeth
are cut at.In the 'stoc' unmodded MTX75 there are only
two types of gear cut,helical on all the gears and
straight cut bevel on the diff gears.The selection of
a lube is based on the cut which in turn tells you the
amount of tooth to tooth load/pressure.The gear cut
that has the lowest tooth to tooth load is the helical
cut,as in the MTX75.If you have a Torsen or Quaife
diff the gears in that type of diff are also helical
cut so you have removed the higher tooth pressure
straight cut gears found in a stock diff .From lowest
tooth pressure to highest the cuts go Low> Helical/
Semi-Helical/Straight/Hypoid>Highest.
The MTX75 does not need lubes for high tooth pressure
so why the hang up on 'gear lube'? An automatic trans
has 'gears' and most all are helical cut gears!!!! For
the sake of history almost all manual
transmissions,the gearbox not the rear end,have for
many years used normal straight or multi-grade engine
oils.If you re read the lab info on Ford honey you
will see that its base is a synth,multi-grade diesel
engine oil....this alone tells you the type of lube an
MTX needs.Why 'diesel'?....Because diesel engine oils
have high resistance to oxide formation and high
detergent propities.....both of which an MTX75
needs.Get off the 'gear oil' hype ,an MTX does not
need 'gear oils' and the main reason ATF was deleted
was due to its effect on the shift fork
bushes....making them tight on the shafts.The only
place for true 'gear oils' is in transmission with
high tooth loads which are set buy the cut of the
teeth,as an example check the lube that should be used
in a Quaife 'straight cut' gearset.Bottom
line....forget the 'gear lube' bunk spouted
around.....A close lube would be a synth ,multi-grade
diesel engine oil!!!!
