If I've let the transmission go without 100k miles, shoud I just continue to not maintain it?

Dear Car Talk

Dear Car Talk | Aug 01, 1997

Dear Tom and Ray:

We recently contacted the local Aamco transmission shop about servicing our
1992 Chevy Blazer's automatic transmission, which is working just fine. The
vehicle has almost 100,000 miles of mostly highway driving. The Aamco man said
that it should have been serviced every 25,000 miles and that it would now have
scale deposits in the transmission and that doing the service now would cause
problems. He said that it were his car, he would now do nothing to the
transmission. We admit we've been negligent in letting it go this long, but is
this guy right? It doesn't make sense to us. -- David and Patty

TOM: It doesn't make sense to us, either, guys. First of all, the recommended
service interval for this transmission is 100,000 miles. So you're right on
time. You haven't been negligent at all.

RAY: And I've never seen a recommendation from Chevy that calls for
transmission service every 25,000 miles under normal conditions. That may be
this particular Aamco shop's recommendation, because they'll make four times as
much money if you do it that often. But I think the guy's wrong on that

TOM: This guy is also perpetuating the myth that "disturbing" an older
transmission will somehow cause irreversible problems (this is also known as
the "let sleeping transmissions lie" theory). This myth is based on the belief
that the transmission has gotten used to its old, dirty fluid. And if you drain
out that loving, old, comfortable, familiar fluid and introduce new, clean,
uncaring, unfamiliar fluid, the transmission will be upset and won't remember
how to work right. This, of course, is complete horse-droppings. A transmission
fluid and filter change is never harmful, no matter how many zillions of miles
you have on the car or how many fish scales you have in there.

RAY: Scale deposits, not fish scales.

TOM: Whatever. David and Patty, you should go to another mechanic and tell him
you are coming in for your 100,000-mile transmission service. And don't worry
about a thing.

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