Monday, May 28, 2012

Piston Slap: Damned if you do…


Kurt writes:

Dear Sajeev,

I'm writing about if/when/how to change the transmission fluid in modern automobiles. It's been my experience when changing the fluid on a vehicle with > 100,000 miles and original tranny, the odds of trans problems within 5,000 miles rise dramatically. The consensus on the interwebs is this was true for older cars, but not necessarily modern vehicles using synthetic fluid. First my history…I'm only listing the cars where I actually changed the fluid. 89 Suburu GL – Fluid Changed at 120,000, total trans failure at 125k. 94 Chevy S10 blazer, trans fluid change at 115k, trans failure at 123k. Current: 2006 Honda Odyssey – Trans Fluid Change at 95K, Torque Converter starting to go out at 100K (yeah, I know this is a weak spot on this vehicle regardless) – wondering if I should change out the rest of the fluid before having someone look at the torque converter?. Additionally what to do about my 2003 Chevy Trailblazer LS (2wd) …..145k, original transmission, original owner, no trans fluid changes ever. The quick lube joint says fluid color is off – looks good enough to me though. I'd like to keep the truck a few more years due to the blood sweat and tears already invested in repairs.

I've read that Trans Fluid power flushes can cause more harm than good, and a standard fluid change only swaps a % of the fluid – normally needing 3 of those to get a full fluid swap. Add the twist of certain vehicles needing "special" fluid such as Hondas and it's hard to say if my failures are due to improper technique by improperly trained quick lube employees, improper fluid, or if changing the fluid isn't really needed! I always say "I'll change the trans fluid when the trans fails". I'm a mild wrench head, some blacked fingernails to prove it ….if my setup allowed it I'd love to change my own fluid – no one cares as much as the owner. However I stopped changing my own fluids after an Exxon Valdez-like accident on my driveway. Any advice on this topic?

Sajeev answers:

Wow, you totally have good luck with transmission fluid changes!  Why not go for a fourth time and see where lady luck takes you?

Or not.

And that's the big problem: usage of the word "or." Because, during hindsight analysis, realizing that your ATF-replacement-cum-gearbox-implosion led to a lot of "or" conversations in your CSI-like TV show analysis of the culprit.  Maybe there was nothing left of the clutch's friction material when the old fluid went in the drain pan.  Or someone put in the wrong fluid.  Or it wasn't enough fluid.  Or too much.  Or some combination of all the previous "or" statements.

Fun, huh? So in your case…

With your driving conditions, track record on transmission failures AND knowledge of the pitfalls associated with these fluid changes in mind…would you do this a fourth time?  I suspect that no matter the machine, your climate, driving style and ATF changing schedule makes this a bad idea.  Don't do it.


from The Truth About Cars

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