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Changing transmission and brake fluid

my Mazda CX9 has 77,000 miles on it and it has never had the transmission or power brake fluid changed. Do they need to be changed and is there a difference between flushing and draining and filling? Which if any do you recommend?

Change them both. You do not want to flush the transmission. Just drain and fill. Flushing can force crud into little passages that crud should not be in.

I usually don’t recommend dealer service, but for tranny flushes, that’s where I take my Acura. Independent shops often like the flush method because it’s easier, faster, and makes them more money. The dealer generally does it right, or they get hammered by corporate.

It’s not a flush. It’s a transmission fluid exchange. That’s because the pump within the transmission is used to exchange the fluid. But since there’s that many miles on the transmission the pan should be dropped for inspection to determine if a fluid exchange is worth it. A fluid exchange replaces all the old/oxidized transmission fluid. Not just 30% of the old oxidized fluid. This explains it.

The brake fluid should be exchanged because over time the brake fluid absorbs moisture from the air. If the moisture contant in the brake fluid gets high enough corrosion can damage brake components. So it’s cheaper to replace the fluid than to replace brake components. Because when you start doing that, you end up replacing the brake fluid anyway.


It’s a good idea to replace brake fluid every 2-3 years, especially if you have ABS.
Re. the trans: also make sure the fluid that Mazda specifies is used to refill, not some ‘universal’ fluid with an additive.