The phenomenon of transmission failure closely following a fluid change in a
neglected unit is no wive's tale. You'll have a hard time finding a service
facility that will do the service on such a vehicle without a signed
disclaimer of responsibility from the car's owner. Not
if they want to stay in business very long, anyway. Almost anyone who's been
in the business very long has horror story(s) about ticked-off customers
demanding a new transmission after
a routine fluid change on a high-miles,
no-maintenance transmission causes
sudden failure within a very short interval. We can argue all day about the
exact failure mechanism, but the scenario is well-known. But it is true, as
someone pointed out, that if such a failure occurs after a fluid change, you
really haven't lost much, since the trans had to be pretty far gone anyway.
Transmissions in good condition aren't
harmed in any way by changing the oil, with the one caveat Dick pointed out
about older cars which originally had the
whale-oil based fluid.
The statement that auto trans fluid does
not wear out in use is only partially true. The fluid has two distinct
functions, lubricating bearings/gears, and
transmitting hydraulic forces. The oil
does not lose its hydraulic function, but it is subject to shearing forces,
and it
does undergo chemical degradation, albeit to a far lesser extent than the
engine's lubricant, assuming the transmission is not overheated. Thus, over
time, its lubricating ability is decreased, hence the recommendation for
regular service. And if the trans is overheated, all bets on the quality of
the fluid are off.
For what it's worth.
YMMV.
Michael
Roger and Michael in San Diego
67 Crown Convertible "Moby"
73 LeBaron Coupe "La Bomba Negra"
56 Sedan
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