Hi there smart drivers, Rick with Smart Drive Test
talking to you today about differentials. This
video on differentials is both for
passenger vehicles and for commercial
vehicles i had a comment from David
lahat and he had a big truck and left
the differential lock on while driving
at highway speeds which is often not
recommended but he wanted to know if
leaving the differential lock on and
driving at highway speeds would cause
damage to the unit because at the end of
the day when you do is post trip down
there in Arizona he discovered that some
of the Humboldt nuts were broken off and
basically at the inside of the tire
there's a hop in the center that's
filled with oil to lubricate the
bearings on the big truck and it's got
bolts on it and some of those bolts were
broken off and he wanted to know if that
was caused by him leaving the
differential lock on and driving the
vehicle at highway speed because it's
not recommended that you drive these
vehicles at highway speed when you have
the diff lock on and it's unlikely that
damage was caused because he left the
differential lock on so we're going to
do today we're going to give you a bit
more information about differentials
what they do and how the differential
lock works on big trucks and as I said
differential is usually the rear axle
and it's the actual that provides power
to the unit and moves it forward whether
it's past your vehicle it's rear-wheel
drive or it's a big truck or up boss so
we're going to be a little bit more
information about differentials talking
about that stick around we'll be right
back with that information
drivers welcome back Rick with smart
drive test talking to you today about
differentials the rear axle of vehicles
that are rear-wheel drive and in this
day and age most of the vehicles passing
vehicles are going to be
front-wheel-drive they're not going to
have a differential however if you have
one of the old muscle cars dodge charger
for galaxy those types of things you're
going to have rear wheel drive and the
vehicle will have a differential
differential the root word of
differential is different and you have
different for different speed of the two
tires on the rear axle and the reason
that you have different speed is because
when you go around the corner it is
required that the outside will go faster
than the inside wheel think of it like a
compass when you're drawing a circle on
a paper the outside of the compass hold
the pencil and goes around the inside
point which holds it steady
that's what happens when you drive a car
around the corner this inside wheel is
fixed and goes at a much lower speed
than the outside wheel because the
outside wheel goes around the outside of
the circle and has to go faster
therefore the rear tires on the vehicle
have to be able to turn at different
speeds
thus you have a differential and inside
here you have warned years and spider
years and all kinds of other things and
if you look around here on youtube if
you want the exact engineering of what
goes on inside of the differential you
can find that information here on
YouTube but i'm not going to go over
that all you need to know is that the
two wheels on the back of the vehicle
that's rear-wheel-drive have to be able
to turn at different speeds in order for
the vehicle to go around corners and
whatnot
now because you have a differential and
you have years in here that will allow
one wheel sort of free play and the
other wheel to go faster
what happens is when you get stuck often
times the differential will direct power
out to the wheel with the least
resistance so therefore you're going to
get one wheel that spins and there's
another video on differential here on
the channel and I show you that on a big
truck if you get one wheel elevated in a
mud puddle and whatnot
it'll just sit there and spin because
the differential direct power out to the
wheel with the lead
resistance so on cars notice things
especially when they want to get more
power and get off the line faster they
have something called positive direction
which essentially locked up the backhand
and it takes off the line because both
wheels are turning at the same speeds
essentially what they do is they lock
out the differential now on big trucks
some buses but not too much more so on
big trucks they have what's called a
differential lock and on the back of a
big truck if you extend this out
usually what you've got is two axles and
you'll have a set of tandem axles here
and you'll have a diff on both axles and
essentially what you have on most trucks
it's uncommon that you'll have a diff
lock on both of these on most structural
have a single diff lock and unlock the
front axle that's for those of you
changing up in the wintertime that's why
they often recommend that you put the
chains on the front axle because that's
where the diff lock is and you put a
chain on each wheel and therefore both
wheels around grind away and move the
vehicle forward over the ice and snow or
whichever or mud or wear whatever
compromise traction conditions you're in
so that's the diff lock now as you can
see here in the image some of the
western stars will have a diff lock for
each axle and maybe two switches on the
dash one for each axle and then they'll
have an interac cyl diff lock as well so
it will lock it across both these both
axles and then it'll lock in between
axles so all four tires all four sets of
tires on the back of the big truck are
grinding away at the same rate and will
not have differential speed as you're
going around corners now for my friend
David who left the diff lock on and
drove at highway speeds which is not
recommended a big truck it's unlikely
that you did the damage to the hub bolt
because you left the diff lock on unless
you're going around sharp corners and on
concrete and asphalt most things it's
really unlikely in one off event that
you're going to do any damage to the top
bolts on the back the actual most types
think is essentially what you're going
to do is you're going to lock all of
this out and as long as you're not
shocking the dr team you're just gonna
wear the tires out
I'll bet is essentially all you're going
to do you're not going to do damage to
have those types of things exactly what
the mechanic told you that it's not what
caused the damage to the hub bolt on
your truck it was probably something
else that happened so that's essentially
a differential those are the
differential locks that you have on big
trucks for purposes of traction and
going at full speed now the other thing
about diff locks and the warning on most
trucks is that you want to stop the
truck or be going at a very slow speed
in a straight line when you engage and
disengage the diff lock you don't want
to be traveling at speed and then engage
it because these gears in here
essentially what you're doing is locking
them up so you don't want to be locking
them up when the vehicle is that speed
or turning and the two wheels are
traveling at different speed so try and
go to slow speed and put the
differential lock on or disengage it
when you're doing that ? drivers have
you left the differential lock on and
had it cause damage the comment down in
the comment section they're all the help
of the new drivers coming into the
industry and starting a career as a
truck or bus driver I'm Rick with smart
drive test thanks very much for watching
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remember pick the best answer not
necessarily the right answer
have a great day bye now
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