"Transmission Flush": Needed ?

Ask them if they drop the pan and replace the filter.[1] This is important because good shifting depends on good flow through the filter and... well, filters get dirty; it's what they *do*. It's also an opportunity to wipe the layer of pond scum from the bottom of the pan. (Unless it has big chunks and/or is there in vast heaps, or is contemporaneous with gross transmission misbehavior, this is assumed to be from normal wear.)

A flush that *doesn't* involve that, usually accomplished via the transmission-cooler lines, changes the fluid, which is good, [2] but does nothing about the status of the filter or about the stuff at the bottom of the aquarium.

I personally prefer to drop the transmission pan every few years, change or clean the filter or screen (whichever it has, if either), and refill with however much fresh transmission fluid is needed to make up for this partial drainage. The disadvantage of this is, it leaves a fair bit of the older fluid in the system.

Nowadays (plus or minus model- or transmission-specific caveats) GM often seems to suggest this at 50,000 miles for severe service, 100,000 for normal service. Back in 1997, Buick apparently billed these transmissions as requiring no maintenance under "normal" conditions:

But then again, long maintenance intervals are widely regarded as a selling point. I'm betting that a good mechanic with field experience knows a thing or two (almost always skewing toward the conservative side) that didn't appear in press releases. If done decently well it shouldn't hurt, and might well help (as evidenced directly by smoother shifts closer to the expected points, and indirectly by longer system life).

Cheers,

--Joe

[1] Some transmissions have a screen that you clean, not a filter; and I guess some have none at all. And some have adjustments that get tweaked while you're at it (in a precise fashion according to the maintenance manual). I am guessing that your car has a filter and no such adjustments. [2] Since it doesn't have an interface with the combustion process, transmission fluid doesn't get nearly as nasty as quickly as motor oil unless there is something grievously wrong with the transmission, and is hardly consumed at all barring a leak; but it does oxidize, and the properties that it's supposed to have degrade, so in addition to occasionally keeping an eye on its level, it helps to change it as a long-term maintenance item.

They recommended (strongly) that you get a "transmission flush" because it's a hugely profitable item for them.

Good thinking on your part. It is neither necessary nor desireable.

A transmission fluid and filter change every 60K to 75K miles (depending on your usage of the vehicle) is not a bad idea, and will extend the life of your transmission, but there's no call for a flush. Your transmission is not a toilet.

Bullshit, NO! They do this because it benefits them, not necessarily you. They need to drop the pan, change the filter, replace the fluid lost. Nothing more.

There have been anecdotal reports of tranny damage due to pressure flushing. I somewhat doubt them, but it is possible.

You dont need it..