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!