Bad to change transmission fluid on higher mileage vehicles???

[Crunch]

Consumer Reports says you shouldn't change the transmission fluid on higher mileage vehicles, Over the years I have heard this from a few other people, and even heard it mentioned on an episode of "Law and Order: Criminal Intent" of all places. The logic is that is shakes loose a lot of debris that clogs critical parts of the transmission, which then fails. Is this true, or some kind of urban legend/wive's tale/jive?

 

[Motorhead]

I think you are pretty safe ONLY doing a pan drain and filter. I think where people run into problems is when they do a pressurized flush on a worn trans. My opinion only.

 

[lpennock]

I think you are pretty safe ONLY doing a pan drain and filter. I think where people run into problems is when they do a pressurized flush on a worn trans. My opinion only.

I agree. Power flush is problem.

 

[FiveFingerDeath]

I've heard that in higher mileage trans, that over time shavings from the clutches flow around in the fluid creating friction on the clutches, so when you drain that fluid and filter you lose all that friction which in turn causes slippage.... idk how true that is tho I'm not a transmission guy

 

[cerberusiam]

NOT flushing the transmission is what causes failures. Leaving contaminated fluid in a transmission is just wasting the 6 quarts or so a pan and filter drop take. Most of the shavings or crud that are an issue are in the pan anyway, the rest are suspended in the fluid. Flushing out the old contaminated fluid is not going to make a difference in failure situations, if it is going to fail it will do it with new fluid or old.

These transmissions cannot be flushed the normal way, only a one way flush which is what the power machines do. Probably the safest way to do it. Failures from a flush are rare and usually due to incorrectly doing it, or, just blaming the handiest thing possible. If the fluid is black or burnt smelling the damage is done and failure is imminent, flushing the fluid out is not going to hasten the end and may extend life to a degree but it is still just waiting for a reason to quit working.

 

[brods]

If my memory is correct I read in a trade mag long ago that there actually was a problem GM had decades ago where the clutch material failed after a fluid change. Iirc it was the glue used to bond the clutch material to the plates. I can't recall if it was because of a fluid spec change, like going from Dexron to Dexron II or if it was just a bad choice of glue, but it was specific to only that one trans for certain years. Here is a quote form another forum where a trans guy lays out why this myth persists today:

Transmission Flush Myths- Busted!

Anyone who is even remotely involved with cars has heard this type of story- someone that they know got a transmission flush and their transmission failed within weeks or even days.

The urban legend behind this is that the "sludge" is all that was holding the transmission together and once it was removed with a flush, the transmission had no chance of surviving.

The story goes like this:
Jim was having a transmission problem, let's say that it was sluggish in the morning and would slip on take-off from a stop from time to time when it was hot out.

Now Jim has a brother-in-law named Bob that used to work on cars, do his own tune ups and oil changes, etc. When Jim mentioned the problem that he was having to Bob, his immediate response was, "You need to get that transmission flushed"

Of course Jim not really knowing anything about a car, much less an automatic transmission blindly follows the advice of his brother-in-law. After all Bob surely knows all about cars even though he hasn't worked on one for over twenty years.

Jim obediently takes his car to the local lube place for a flush and an engine oil change while it's there. Jim gets his transmission flush, pays and goes on his way.

At first, he notices maybe a slight improvement in performance but his transmission is still exhibiting most of the original symptoms.

About two weeks later Jim is driving to work and he stops to pay a toll. When he tries to pull away from the toll booth the unthinkable happens- the car just revs and goes nowhere, as if it is in neutral. Jim moves the shifter into low and is able to limp his car off to the side of the road and wait for a tow truck to take him to a transmission shop.

What happened?

Here's a list of reasons why the transmission flush myth exists:

•The myth is propagated by people who claim to be experts. I have even heard of transmission repair shops who contribute to the myth in the hopes of scaring potential customers into having their transmission overhauled rather than maintaining it.

•There are thousands of "internet experts" who promote the misinformation- it's truly a case of "monkey see, monkey do" on steroids!

•There may have been a time in the early days of automatic transmissions when failure after a flush was more common, perhaps because of antiquated friction material and transmission fluid technology during the 1950's and 60's but this was before my time so I'm not able to truly discuss the legitimacy of the possibility. I can, however, say with certainty that it's not an issue with 99.9% of the vehicles in service today. If your owner's manual is in the glove box and not painted on the wall of a cave, you are probably good to go.

•"Sludge" is all that was holding the transmission together and when it gets cleaned out the trans in going to fail immediately. Guess what? If you have sludge in your transmission, it's already bad and in need of a repair.

•Once in a while a flush is performed, usually at a quick lube operation, and the transmission is not refilled correctly- resulting in failure soon thereafter. Of course the incorrect fluid level is not recognized as the culprit- the transmission flush is! Many automatic transmissions have fairly complicated fluid level checking and filling procedures that are best left to a transmission repair expert to perform.

•People have unrealistic expectations. A transmission flush is no more likely to fix a failing transmission than an engine oil change is to fix a major internal engine problem. Both of these things are great to do regularly but they are maintenance- not a fix for a problem.

•The reality is that most people don't think about their transmissions until the day that they have a problem. Jim's transmission was on borrowed time- it was going to fail anyway but now that it has, he is going to perpetuate the myth. If he ever hears someone mention a transmission flush, he's going to proclaim, "I had that done and my transmission blew up within a month!"

I have been in the transmission repair industry since 1987 and can honestly say that I can't recall a single time where I saw a healthy transmission get a flush or a fluid change and subsequently have a problem. A transmission flush is the best maintenance that one can do to extend the life of your automatic transmission, don't miss out on the benefits because of the nonsense that exists surrounding changing your transmission fluid!

Anyone can feel free to repost this as long as you leave the "about the author" part intact.

About the author:
John Lombardo is co-owner of IPT Performance Transmissions and has been in the high performance industry for over 20 years.

As for the "power flush" I have never had a decent explanation of how the power flush specifically works (one service manager said it back flushes the filter so the filter doesn't need changing) and if it doesn't use brand new fluid, to me its like taking a shower and then putting your dirty underwear back on. Do a search on the forum to see the procedure to fully change the fluid and filter yourself.

 

[cerberusiam]

As for the "power flush" I have never had a decent explanation of how the power flush specifically works (one service manager said it back flushes the filter so the filter doesn't need changing).

That is part of the "flush" myth that gets perpetuated, back flush indeed! LOL!

A fluid exchange using a machine works the same way as DIY method, just less mess. The input to the machine is the cooler output of the trans, the output is to the cooler input of the transmission. The exchange machine just pumps clean fluid into the sump thru the cooler return as the transmission itself pumps the old fluid out. It is actually better than the DIY method as fluid is never run low at any time.

 

[Wayne M.]

For what it's worth, I believe any high mileage AT needs to be thoroughly evaluated before any maintenance is done. Shift quality, converter lockup and OD shift efficiency to start all must be evaluated to give the unit a consideration for fluid change.
In my personal experience with the 44RE in my '98 Durango, I've had exceptional life from that unit. It wasn't easy. See, I bought "red" as she's called, off a lease in '01 with 19k on the clock. Knowing full well of the shortcomings of the RH's and RE's and their expected lifespan of months and not years, I decided to take on a severe duty maintenance cycle with this unit.
For the time it was in a hard moms NYC taxi service cycle, I dropped the pan every second or third summer, put a mopar filter, and refilled with ATF+4 exclusively.
Nowadays it's a 3rd car fill in for days I don't feel like shaking hands with the Ram, or going to the door ding mall.
Today it has about 120k on the clock. There's no delay into D after a week sitting, plants you in the seat on 1-2 and 2-3, has excellent TC lockup and OD apply.
People don't believe that the unit has never been down. This and sucky fuel mileage are the main downers with this truck.
Basically IMHO, prevention is the key in any automatic. There's no such thing as lifetime sealed pans. I believe keeping the fluid fresh keeps all the seals and other components fresh as well.
Back to the OP, change old ATF in an unknown unit? Total crapshoot.

 

[brods]

That is part of the "flush" myth that gets perpetuated, back flush indeed! LOL!

A fluid exchange using a machine works the same way as DIY method, just less mess. The input to the machine is the cooler output of the trans, the output is to the cooler input of the transmission. The exchange machine just pumps clean fluid into the sump thru the cooler return as the transmission itself pumps the old fluid out. It is actually better than the DIY method as fluid is never run low at any time.

Yeah that service writer was an idiot and it was clear there was not point to listening to his sales pitch bs any longer. Anyhow, how is a power flush better than DIY if they don't clean the pan or change the filter? Also, I seem to remember reading about several variations of the power flush machines, one of which filtered the oil and returned it to the trans. And since the machine had to have a reservoir of fluid, unless you were the very first flush with the machine, your trans oil would be mixed with the residual fluid from the previous flushes! Even if the machine uses new fluid, how is it going to get out accumulated debris or clean the magnet in the pan? And either way you still have a dirty filter! I'm with Wayne on this one, drop the pan and look for things that shouldn't be there (lol), clean the magnet, install new filter, refill with new fluid and empty the converter while adding new fluid as described on the forum.

 

[cerberusiam]

The exchange machine is meant to be used AFTER a pan drop, not without it. Some will tell you that it will clean the pan and filter but they know about as much as some service writers, there is no replacement for dropping the pan to clean it and replace the filter.

The typically used exchange machines do not mix fluid, there is a membrane between the old and new fluid that dose not allow mixing. The exchange machine is marginally better as it will flush the old fluid and any build up out of the trans drive train as the fluid is exchanged, the DIY process does not do that until you hook the return line up again. It allows a little better flush of the complete trans as the old fluid gets pushed back into the sump then picked up and routed thru the cooler system and extracted. It is nuance difference but machines do get that extra 2-3 quarts in the cooling\lube system out better than just dropping the return line.

 

[brods]

The exchange machine is meant to be used AFTER a pan drop, not without it. Some will tell you that it will clean the pan and filter but they know about as much as some service writers, there is no replacement for dropping the pan to clean it and replace the filter.

The typically used exchange machines do not mix fluid, there is a membrane between the old and new fluid that dose not allow mixing. The exchange machine is marginally better as it will flush the old fluid and any build up out of the trans drive train as the fluid is exchanged, the DIY process does not do that until you hook the return line up again. It allows a little better flush of the complete trans as the old fluid gets pushed back into the sump then picked up and routed thru the cooler system and extracted. It is nuance difference but machines do get that extra 2-3 quarts in the cooling\lube system out better than just dropping the return line.

I guess none of the dealers pushing the flush got the memo that the pan needs to be dropped and the filter changed, lol.

Also there are different machines out there, some supposedly use cleaning solution while others as you describe are just fluid changers. Some hook up to the cooler lines others require dropping the pan and connecting to the filter port. Some have pumps others use the transmission's pump. Given the chance of getting a straight answer from the service writer about how their machine works, I'll just pass and do it the old fashioned way.

 

[cerberusiam]

An exchange machine only works one way, a flush machine back flushes and does other things that are BAD. Problem is the description are used interchangeably so if the service writer is a dolt you never know what you get.

These cooler systems cannot be back flushed like others, it does no good and in some cases will cause a failure of a brand newer transmission. Reason why most places require a new front cooler and line flush if the trans was cooked and really toasted.

If not sure, DIY is better than trusting to the unknowing and for the most part uncaring service people.

 

[Crunch]

Some very interesting and good responses here. Thanks. So I guess the idea that changing the transmission fluid is bad goes in the urban legend column, next to the one about people eating an average of 8 spiders a year in their sleep. On the other hand, exchange is good, back flush is bad and never trust what goes on in the service department unless you know them really well.

 

[Wayne M.]

***APOLOGY***
I just came back to check on this thread and noticed a "dislike" thumbs down. You don't see them often, so I wanted to see where it was in this topic. My hair stood up when I saw it was me.
That was not intended, and was probably a misfire. I didn't know I did it, and don't know how to undo it.