[Shop-talk] Auto xmission fluid change

[BJNoSHOV8]

I've always wondered why manufacturers don't put drain plugs in 
transmission pans.  But then now a lot of transmissions are sealed units 
and you can't even add fluid to them.

My father has owned his own garage for over 50 years and when I was 
working there we typically would do the drop pan/replace pan/refill method.

About 10 years ago I got a Taurus SHO and the online owners group had a 
different procedure for changing the fluid.  Working from memory here... 
they would pull the cooler line hose off of the cooler just behind the 
bumper, let the engine run with fluid being pumped out of this line 
until the flow slowed down, stop the engine, drop the pan, change the 
filter, put the pan back.  Then they would add something like 10 quarts 
of fluid to the trans, maybe more I don't remember.  Start the engine 
and let it run while it pumps out fluid until the color of the fluid 
changes, then stop the engine, reconnect the cooler line, fill the 
transmission to the correct level and you are done.

I did this procedure with my first car and it worked fine.  Then I sold 
that car and bought another one, one with low mileage.  When I tried the 
procedure with the second car the trans would pump the fluid out very 
slowly.  I completed the fluid change and 10,000 miles later the 
transmission self destructed (60k total miles).  The bushing that the 
torque converter runs in failed, maybe the pump failed first.  I had the 
transmission rebuilt by what was supposed to be the best shop in town.  
10k miles later the transmisson failed again.  Unfortunately those 
transmissions were known to be failure prone, I just got lucky with the 
first one.

I think there are lots of people that never change transmission fluid 
over the life of the car.  I have seen some cars with 100k miles or more 
that would start slipping, probably never had the fluid changed before, 
and after putting in a new filter they worked fine again.

Of course YMMV.  I am a believer in regular fluid changes according to 
the interval recommended in the owners manual.

> One thing I did do (and recommend to others) was to install a drain in the
> pan - drilled a hole, and installed the fitting (bolt on the inside to hold
> it to the hole.