Come on now! You should know the argument about this topic by now.

 

Aww come on...One more time.

 

The pieces of crud that have built up in the trans MAY be all thats holding certain things in place properly... flushing removes those, and thus causes problems...In a tranny thats been well maintained and flushed regularly, doing a flush is no problem, because there are no "Pieces of crud"..... In a poorly, or unknownly well maintained tranny....it can be an issue........I believe that's the argument.

 

Flushing is generally running some kind of solvent, or, high detergent trans fluid backwards thru the trans. That gets the dirt broke loose all right, but, it does NOT get it all out of the trans. A fair bit accumulates on the WRONG side of the filter, so, the first time you start it up, and put it in gear, all that crap gets run right back into the trans. All at once..... Tends to foul close-tolerance parts, like the valves in the valve body, and clog small passages. Basically, the trans stops working right.

There is another style of 'flush', that splices into the trans cooler lines, and simply replaces fluid at the same rate the trans pushes it out. NOT recirculating the old stuff. This type of flush is hideously expensive, as it uses a LOT of trans fluid. It has the advantage of anything that it does happen to break loose, is pumped out of the trans in the correct direction of flow. These types of machines aren't real common though, as this style of service is significantly more expensive than the other style.....

 

im going to agree with HeyYou right up to the point where he says that the mechines are not used and expencive. yeah 100 bucks to run the tranny frush is a bit high. that out cost to run the flush which is powered off the trans pump does not force fluid into the valve body or threw the tranny. also we normally do whats known as a two filter flush thus why there 100 bucks. we replace the first filter with a vert fine filter to catch sedilment from the flush. then we flush the trans and then we replace the filter with a stock one. most shops dont like to waste the time to do it right so the flush with the dirty filter and think they helped by changed bad fluid to good. also as much as everyone argues that new fluid makes it not move BULL FING $hit. the trans came with clean not dirty fluid that worked just fine shifted and everything. its goon do it again with the same clean fluid. also i would recommend MAXLIFE trans fluid it capadable with 90% of trans and dealers and makers also had added sulavents so brake down slug and grime and also to help bands from streching and swelling.

 

When the trans came new from the factory, all the parts in it were new too..... after 100K miles, they aren't new anymore. Doing a flush IMPROPERLY is highly likely to kill the trans. Doing it the right way has a chance of killing it as well. At the dealership I worked at, we warned folks with high mileage automatics that it was a possibility. At the independent shop I worked at, we simply would not do a flush. Fluid and filter, sure.

 

I still cant grasp that removing all the fluid from the trans and replacing it with new will kill it.

 

From what I understand Its not just replacing the fluid. In a flush they are running solvents through it to break up all the crap in there. It seems that not all of the crap gets out with the flush and some is left behind. Now once you run trans all the left over crap gets lodged into places it shouldn't be (like the valve body) and the trans can no longer work like it should.