In general, could a trans flush be harmful?

[d72hemi]

I hear the tales that a trans flush could cause a transmission to fail nearly immediately or within a 1000 miles or so.  I understand that trans flush is not a magic cure for a toasted trany, but how will a flush kill one? Is this an "old wives tale" or is there some validity to this?

If true, the only things I can think of is that the new fluid dissolves/loosens "gunk", and  the floating "gunk" clogs parts of the trany. Or the old burnt, and thereby thicker trans fluid was making up some of the difference in worn parts.

The reason I ask is that the local trany shop did not want to flush the trans on my grandfather's 92 Camry since the fluid looked closer to used motor oil than trans fluid, but they did drop the pan, change the filter, and the few quarts the pan held. I did a "flush" on my Charger's trany one pan drop (cheated with a drain plug) at a time and it worked the same (intermittent  3rd).

[myk]

People will argue back and forth on this like they will what oil to use.  During my stint at a Valvoline shop I had to make my customers sign a waiver that stated that Valvoline would not be liable for any future damages or failures with a transmission that receives the flushing procedure.  Some say that a flush won't destroy a transmission but ONLY, and ONLY if it is done properly.  Personally, the transmission is a machine, just like an engine-its lubricants decrease in effectiveness over time and it only benefits you to change it.  

As far as my experience goes if a transmission has had regular service intervals you can keep servicing it accordingly.  But, if the fluid is never changed, some people say that transmissions come to depend on the garbage floating around in there to maintain frictional properties between parts-to clean all of it out with fresh fluid would kill it off.  But, if you're like me and you buy a '99 Ram Air Firebird and you don't know if the fluid has ever been changed, just do a pan drop, filter change and refill. It's like getting the best of both worlds: at least you have some fresh fluid and a new filter, but you keep some of the old fluid in there if the transmission gods want it in there.

Either way, it's a crap shoot but I say pan drop and refill...

[Cooter]

A "Flush" will not kill your trans...Running the wrong fluid will...Waiting till the trans is slipping to flush it will....TOWING while in OVERDRIVE in town will kill a trans...This is why this is heard this way...No wives tail about it...A few people in the auto industry began to try and talk customers into flushing transmissions and saying stupid sh*t like "It'll make your trans live so much longer, shift better, and won't slip." While this is true, the average Joe Public began to think that his 250K mile transmission that has begun to flare high gear can be helped with a "Flush"..When it didn't and the trans "Went out", then is where that stupid sh*t of "A flush killed my trans" began...Like a light bulb that blows in your house..Who's fault was it? Was it yours for using up all the good in that bulb, or the guy/gal that flicked the switch the next time?

[Plumcrazy]

I'm not a fan of fluid flushes. I want to see what the filter looks like and whats laying in the pan.

And if you loosen the valve body bolts you will get most of the old fluid out.

[flyinlow]

I'm not a fan of fluid flushes. I want to see what the filter looks like and whats laying in the pan.

And if you loosen the valve body bolts you will get most of the old fluid out.

Good advice.