Here’s Why Changing Your Transmission Fluid Can Cause Damage


rev up your engines, today I’m going to help
you answer the question, can changing your transmission fluid cause damage to
the transmission, now people are always asking me, Scotty some guys tell me
don’t change the fluid my transmission that it may start slipping or stop
shifting gears right, is that true or not of course you don’t want to damage your
car by not maintaining it, but on the other hand, you don’t want to maintain
your car and then damage it through the maintenance you’re doing, so here’s the
truth, a little history helps explain it General Motors made the first really
commercially viable automatic transmission using hydraulic fluid to
drive the transmission, instead of using a manual clutch, where the clutch is
clamped down to the engine and when you step on the clutch it releases it, so you
can shift gears and when you pick up on the clutch it goes back down so the
engine and the transmission are mechanically connected, an automatic
transmission uses what’s called a torque converter, there’s fluid inside and even
though the torque converter is bolted to the flywheel on the engine is
mechanically connected, the connection between the torque converter and the
transmission is using fluid dynamics to make it go, it’s not physically connected
and they have to make them that way for one reason, when you come to a stop in a
standard transmission, you have to push down on the clutch or put it in neutral,
or the car will stall out, but with an automatic, that doesn’t occur, while
you’re sitting there, the torque converter just has complete slippage and
so the car doesn’t stall out from the engine being jammed against a piece that
isn’t moving anymore, here’s a torque converter taken apart, you can see
there’s all kinds of little crevices and friction plates, the fluid allows the
mechanical spinning of the engine to be transferred to the transmission using
fluid pressure and fluid friction, now because this transfer is done in very
small spaces, it requires a very thin clean fluid, if it was thick it would
just jam the whole system up and not work right, and believe it or not the
early automatic transmissions some of them used whale oil, talk about save
the whales, we were killing the whales to drive our cars, so
guess what you need clean fluid in your transmission or it won’t work right now,
years ago when I was a young mechanic, we changed the fluid and filter in
automatic transmissions every twenty or thirty thousand miles to keep them
running smooth, but today modern fluids have a higher quality as do some of the
transmission parts, some of them use fully synthetic fluid, you still do need
to change it though regardless of what anybody’s going to tell you, if you want
your vehicle to last for hundreds of thousands of trouble-free driving, now
the fluid in the Celica has been changed every 40,50 thousand miles I’ve changed
it and it’s got 240 thousand miles on it still has the original transmission and it
shifts like a dream, but if you have not maintained a transmission correctly and
now say you got a car that’s got 150 thousand miles on it, the fluids all
black and you think, gee I’m going to change it, well guess what that may not be a
good idea, because if you have a really dirty transmission, your torque converter
is working with dirty fluid, dirty fluid has more friction, that may be the only
thing that’s still making it drive down the road and not slip, you change out
that really dirty fluid, hey I’ve seen many people do that and what happens is
they slip or they don’t even move on their own, that you’re really better to
leave alone if the transmission is still working, you’re living on borrowed time
then anyway, or you might try some of this Lucas transmission slip fix, which
works like this, if you have a high mileage car, with really dirty automatic
transmissions, you can get a bottle of this Lucas transmission slip stop, it’s
24 ounces, you drain 24 ounces of fluid out of the transmission and only
24, and then you add that into the automatic transmission, sometimes that
can keep it from slipping, the ones that have already started slipping, and if you
have really dirty fluid it can at least protect it for a while longer, realize
that automatic transmissions hold a lot of fluid, some of them hold 14,15 quarts
of oil, so if you just drain out 24 ounces, and put in 24 ounces of this,
you’re not radically changing the consistency of the fluid like you would
if you drained it out and put all clean fluid in a dirty transmission and then found out, oh my god it’s slipping now what am I going to do, but of
course you’re better off changing the fluid regularly in the first place, not
getting into such a mess, and I know some people are going to say, Oh Scotty those
new cars say it’s lifetime fluid, you never need to change it well, if you’re
going to keep your car as long as possible that’s a bunch of nonsense, it still
needs to be changed I talked to my transmission man about
that and he says, Scotty you should see some of these cars, we advise them even
though it says lifetime, change it every 50,60 thousand miles
even with synthetic fluid, because we’ve seen the ones that have a hundred
thousand miles 120 and they break and when we take them apart,
there’s nothing but crud inside from it breaking down, he told me that he’s seen
tons of Nissan’s that if they will only change the fluid every 50-60,000
miles even though it said it’s a lifetime fluid, that he wouldn’t have had
to rebuild those things so soon and spend four or five, six thousand dollars
on a job that, hey if you change the fluid and paid a guy like him 100
something dollars to do it, you wouldn’t be in that mess in the first place,
regular maintenance is the key here, like I said, if you wait too long and it’s too
dirty, with too many high miles on the car, if you do change the fluid, a lot of
times the transmission will go out entirely,
and then you’re going to have to spend a ton of money fixing it, because this
Lucas stop slip, hey it’s basically just a band-aid, it might get you a little
more time out of a transmission that’s really dirty and isn’t working right, but
it’s not a miracle it’s not going to rebuild your transmission because it was
all ruined from dirty fluid, and to give you one more warning, people always
asking me about transmission flushes, my advice never flush out an automatic
transmission, too much damage can be done by pushing dirt into small crevices, when
you change it, you drop the pan, you change the fluid, and the filter if it
has a filter, and leave it at that, the flush machines they can cause more
damage than good that they might do, so now you know the truth about automatic
transmission fluid changing, and if you follow my advice, and buy the right car, you
can have many miles of trouble-free shifting in your car, because
some cars they just have poorly manufactured automatic transmissions, and
it doesn’t matter what you do to them they’re going to fall apart well before a
hundred thousand miles anyway, but if you do pick the right manufacturer, you can
get this kind of mileage out of a transmission and even more, so if you
never want to miss another one of my new car repair videos, remember to ring that
Bell!