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A few years back, perhaps 2, someone who worked for GM got real agro about people complaining online about the effects of Dexcool on relatively new cars. In response, in perhaps 5 minutes I had found over 900 individual references online for the week in question of people complaining about 'x' failures due to dexcool. Point being, where there is smoke there is fire. Unlike internet rumors (Bill Gates gives you a million bucks if you send an email) complaints come from single point sources: i.e. "My car broke down today due to yyyyyyy"
Ignoring the fact that no repuatable tranny shop on the planet will flush a tranny (and why not, the flush service costs more than a pan drop and takes less labor) lettuce consider:
You will hear complaints like the following:
"My transmission died". And this can be backed up by 'good science' - trannys do die from normal use. But the rate of failure is actually very small. The 89-92 taurus tranny is considered one of the worst, but its worst year (91) it failed 70 per 1000 by 75K miles. Or in other words, by the time the 91 reached 5 years old appx 4200 trannys failed per year on average. Thats not a whole heckuvalot to go around..but you see how the perception runs. There is a perception tauri are to be avoided.
"I changed my fluid by droppin the pan and soon thereafter it died". There is also some good science here. IF the tranny was very worn and 'close' to failure, the re-swelling of the seals from new fluid could hasten their destruction - but mind you, this occurs typically on only very high mileage, high abuse cars and the incidence is rather low. The perception is the practice is safe and without risk.
"I had my fluid flushed by Jiffy Lube and soon thereafter it died". There is real good science behind this. According to a fairly recent issue of either Motor or ATRA magazine (within the last year) it has been noted that 3 out of 10 trannys flushed need a rebuild within 5000 miles. This is regardless of mileage, condition, age. Some people might say: "yeah but by the time you decided you need a flush, it was too late" and Im sure the liability lawyers like this. 3 outta 10. thats 300 per 1000 or 4 times the failure rate of the 91 taurus. And its mileage independant. I smell smoke.
the outlying reason is thus: People either work on their cars themselves for the maint chores, or they do not work on the cars themselves. People that do work on them tend to be 'net connected' more than people who do not. People who do not work on their cars, be it housewives, elderly, apartment dwellers - whatever - must rely on others for basic maint. Changing a tranny is basic maint and there are enuf commercials on TV that one can conclude its not a well guarded secret. Tranny shops do not flush. Jiffy Lube does, but Jiffy Lube does not repair. A damaged tranny owner will seek remedy elsewhere. Im sure they will first contact the shop owner, whose livlihood DEPENDS on selling such questionable practices, and who will give the 'yeah but it was close to failing as is' speech and NOT report failures to the general public or online.
And lo and behold, within a few minutes, any person reading this can google search and find thousands of links to incidences of trannys failing right after a flush. If we are willing to suspend reality for a few moments I guess we can conclude that people only flush trannys at the end of the service life of their car. But that also requires us ignoring the large finished lubricants market for ATF and the parts market for filter kits - including late models.
And finally getting to the nut of the problem as to why the trannys fail: flushing them, ESPECIALLY without a pan drop, stirs up the matter that WILL be in the pan or collected in areas of 'dead flow'. This matter is no longer in microscropic particle format in suspension, but has now congealed and is clumpy. It will cling to the metal particles that WILL be there. This material WILL be deposited on seals and cluthes. It WILL cause shift valves to bind. If you delay the throttle valve on a 4L60 by a few milliseconds, the tranny will fail spectacularly within a few hours of operation. (for example)
And of course, unless the flushing shop uses a chassis dyno, which they dont, they will not flush locking converters, any valve body circuits, and only a portion of the cooling circuit which is now universally thermostatically controlled.
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