transmission service or not


Original poster
Dec 28, 2012
My 2003 trailblazer ext has 129k on it and has never had the transmission serviced. It shifts fine, no issues. I was talking to my mechanic about changing the fluid and filter and he said you might want to think twice about doing it at this point. Not that it has happened with a trailblazer, but he had some vehicles transmissions go bad after they were serviced that had high miles with never being opened up before. he sad sometimes it's not worth opening them up.


Aug 26, 2012
I would do the 100k service.

drop pan, clean out the shavings/inspect the pan and magnet, replace the filter and at least five quarts of DEXRON-VI. If you are picky, also change out the rest of the fluid via the transmission line to the radiator.

plenty of discussion on this elsewhere.

Boricua SS

Nov 20, 2011
its been heavily debated whether to flush or not to flush a 100+k mile tranny...

if it were me, i would just do a pan drop, and filter change... 5 to 6 qrts at most of tranny fluid.. but i would not flush the tranny...


Lifetime VIP Donor
Nov 19, 2011
Portland, OR
I'm mildly curious about why you bought or allowed to happen in your watch, such a neglected tranny. But it won't change my advice. There is a HUGE amount of urban legends and on-line debate about skipping the fluid change on an old transmission. Many mechanics even reinforce this myth by remembering each tranny that failed soon after a service, and conveniently forgetting the ones that live on (because they never return if they survive).

If it's neglected, service it. If it fails, it was destined to fail anyway. And that will reinforce the lesson that stuff needs to be serviced.

Anything else is rationalization and misplaced frugality. (IMHO - see my avatar)


Aug 26, 2012
if you do it yourself, be careful and put the pan bolts back in by hand (and use a small torque wrench to spec)

If you pay to have it serviced, ask to see the old filter, and check for leaks.

have you checked the fluid level in the trans?

Lima Tango

Dec 4, 2011
Drop the pan, replace the filter and fluid with Dex VI. It's not a difficult or expensive job to do yourself even if you need to buy a couple sockets and inexpensive torque wrench to do it, and you'll know you did it right. You'll either increase the life of the transmission or it was about to fail anyway.

While you're at it, great time to add a transmission cooler!


Dec 4, 2011
I'd do it.

Heck a horribly overdue transmission flush on my brother's old beater actually brought that transmission back to life and the guy who got it from my brother still drives it now. It was slipping real bad, not going into gear, etc. Fluid looked like mud. Flushed the whole thing and it shifts just fine again.

Mine hadn't been changed on time either (overdue when I got the truck) but that was almost 60k ago. I did a total fluid replacement too, not just a pan drop.

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