Sludge is a by-product of combustion and the Transmission fluid is not exposed to combusion gasses so it does not build up sludge..
Transmission fluid becomes dirty with particles worn from the friction material on the internal clutches and bands. These products contaminate the fluid and make it dark and muddy colored. Heat can and often is the major cause of fluid damage. Heat can destroy the fluid and cause it to form varnish deposits which can cause some valves and check balls in the valve body to stick.
The detergents in fresh transmission fluid will not loosen or remove fluid that has been burnt and created varnish deposits.
If a transmission failed shortly after a fluid flush, then the transmission was going to die anyway and it had nothing to do with the fluid flush. Or, it is possible that they put the wrong type of fluid in the transmission which caused the failure...That can be tested and if the wrong fluid was used, the shop could be sued in small claims court for the cost of the transmission repairs and the testing of the fluid.
That is one of the problems that mechanics have to face nearly everyday. Someone thinks their transmission is acting up and they get the fluid flushed. The flush cannot repair the problem, so the customer blames the shop that did the flush for their transmission problems.
Yes, there are ships that I would not trust to put the valve caps back on my tires after checking the pressure, let alone even getting the pressure rignt. That's why it's a good idea to check with your friends and guys you work with as to who is a reputable mechanic. This is not likely to be the guy who works out of his backyard garage and hangs drywall during the day. To work on todays vehilces requires a lot of training, experience and special tools and test equipment otherwise the guy is just guessing and changing you for the parts while he's learning.
Any mechanic or ship that advises against a transmission flush does so only because they don't have the money to buy the expensive, single-task machine. And yes, it is normal for the ships with the transmission flush machines to charge more for a flush than a conventional fluid change because they need to pay for the machine within a relatively short time. There are far less return problems when the flush machine is used than the conventional fluid change since they don't remove the pan, they cannot be blamed for transmission pan gasket leaks.
One of the biggest reasons why people don't like the flush is because it does not change the transmission filter. If you flush your transmission regularly, the filter will easily last over 100K miles. Also, the filter in the transmission does not function the same way the an engine oil filter, or air filter.
Oil and air filters use many layers or thinknesses of filter material to trap and hold contaminates. A transmission filter is a thin flat filter used to block larger particales of contaminates from getting pumped back through the trasmission. It is not desinged to trap and hold particles. When the engine is shut off the transmission pump stops and the material trapped by the filter will fall harnlessly to the bottom of the pan where it will be attracted to the magnet and will stick there until the pan is removed. As long as it's sticking to the magnet it's not suspended in the fluid. Any particles that get past the fliter are too small to cause damage to the transmission.
If your tranmission is slipping, it is generating excessive heat. That damages the fluid and causes more wear of the friction material which leads to more slipping and more heat. If your tranmsission is slipping, you need to have it checked out before the clutches and bands are damaged beyond repair and the transmisison must be rebuilt.
Some debris in the bottom of the transmission pan is normal. How much is normal wear? It depends on the transmissi
