RF Overlord
73 is the best number.
Many people are either confused or have been given misinformation about the proper way to change transmission fluid and filters.
Flushing will kill your transmission: Fact or Fiction?
Joe Sixpack drives his car for years without ever giving a thought to the transmission until one day it starts making a funny noise or shifting strangely. Since it's about due for an oil change, he mentions the problem to the "technician" at Jiffy Lube, who sells him a "transmission flush". Three weeks later, the transmission croaks. Since the flush was the last (and only) thing done to it, OF COURSE that's what killed it, right? It couldn't possibly have been the years of neglect and abuse. The reality is that the transmission would have died when it did whether the flush had been done or not. If you wait until the transmission is acting up and the fluid is all burnt and nasty, you're living on borrowed time. Go ahead and change it...you may add some life to your transmission, or it may die anyway, but if it does die, it won't be BECAUSE you changed the fluid.
Flush or Complete Fluid Exchange?
Second, there is a lot of confusion surrounding the word "flush". Many people mistakenly believe that it means to somehow force fresh fluid backwards through the transmission, disturbing all kinds of sludge and what-not stuck in the filter and in the various passages and lodging it in important places of the innards. If that was even possible (which it isn't), there's no valid reason to do it this way.
Every fluid exchange (and that is the preferred term) machine I've ever seen works passively, in more or less the same fashion: by using the transmission's own pump to push old fluid out into one end of a double-ended cylinder divided by a sealed piston. The other end of this cylinder contains fresh fluid. As the old fluid enters the cylinder, it pushes against the piston, which causes the fresh fluid to be pushed into the transmission in the same direction, and at the same pressure, as fluid flows when the transmission is operating normally. Here's an example. For those who may not be aware, this is the exact procedure recommended by Ford in the factory service manual.
For times when a complete fluid exchange is not called for, such as during routine maintenance, a simple drain & fill will exchange approx 4 quarts of fluid, which is about 25% of the total capacity. This is sufficient to keep the fluid fresh when performed at intervals appropriate for the vehicle's operating conditions. Installing a $10 drain plug in the back side of the little "well" in the bottom of the pan makes the job as easy as draining the motor oil.
The Filter: Less important than you think
Now to filters. An automatic transmission is a sealed system, with no air intake to draw in contaminants and no combustion to create by-products, so the only thing the filter needs to catch is internal wear material. Most wear in an automatic transmission occurs during the first 10,000 miles of use from new, and it is this initial wear material that the filter is designed to catch. Changing the filter once, preferably at the 10-15,000-mile point (more or less) is a good idea, but from that point it is not necessary to change it again if the fluid is kept fresh. According to the factory service manual, it is not required to routinely change the filter unless the transmission is being repaired for a failure or is being serviced for fluid contamination.
Flushing will kill your transmission: Fact or Fiction?
Joe Sixpack drives his car for years without ever giving a thought to the transmission until one day it starts making a funny noise or shifting strangely. Since it's about due for an oil change, he mentions the problem to the "technician" at Jiffy Lube, who sells him a "transmission flush". Three weeks later, the transmission croaks. Since the flush was the last (and only) thing done to it, OF COURSE that's what killed it, right? It couldn't possibly have been the years of neglect and abuse. The reality is that the transmission would have died when it did whether the flush had been done or not. If you wait until the transmission is acting up and the fluid is all burnt and nasty, you're living on borrowed time. Go ahead and change it...you may add some life to your transmission, or it may die anyway, but if it does die, it won't be BECAUSE you changed the fluid.
Flush or Complete Fluid Exchange?
Second, there is a lot of confusion surrounding the word "flush". Many people mistakenly believe that it means to somehow force fresh fluid backwards through the transmission, disturbing all kinds of sludge and what-not stuck in the filter and in the various passages and lodging it in important places of the innards. If that was even possible (which it isn't), there's no valid reason to do it this way.
Every fluid exchange (and that is the preferred term) machine I've ever seen works passively, in more or less the same fashion: by using the transmission's own pump to push old fluid out into one end of a double-ended cylinder divided by a sealed piston. The other end of this cylinder contains fresh fluid. As the old fluid enters the cylinder, it pushes against the piston, which causes the fresh fluid to be pushed into the transmission in the same direction, and at the same pressure, as fluid flows when the transmission is operating normally. Here's an example. For those who may not be aware, this is the exact procedure recommended by Ford in the factory service manual.
For times when a complete fluid exchange is not called for, such as during routine maintenance, a simple drain & fill will exchange approx 4 quarts of fluid, which is about 25% of the total capacity. This is sufficient to keep the fluid fresh when performed at intervals appropriate for the vehicle's operating conditions. Installing a $10 drain plug in the back side of the little "well" in the bottom of the pan makes the job as easy as draining the motor oil.
The Filter: Less important than you think
Now to filters. An automatic transmission is a sealed system, with no air intake to draw in contaminants and no combustion to create by-products, so the only thing the filter needs to catch is internal wear material. Most wear in an automatic transmission occurs during the first 10,000 miles of use from new, and it is this initial wear material that the filter is designed to catch. Changing the filter once, preferably at the 10-15,000-mile point (more or less) is a good idea, but from that point it is not necessary to change it again if the fluid is kept fresh. According to the factory service manual, it is not required to routinely change the filter unless the transmission is being repaired for a failure or is being serviced for fluid contamination.
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