is it a bad idea to change REALLY bad tranny fluid?

[82DMC12]

Group,

In searching through the archives, i haven't seen much on this topic. i have heard from some people that if the fluid is pretty dark/burned, you will do more damage flushing the transmission fluid than if you just leave it alone.

is this true? what is the reason? what exactly will happen if you change really bad fluid and what causes the transmission to need an overhaul soon after? lastly, how would you determine the fluid is beyond service. obviously you should have changed it as needed but we are assuming you didn't.

This has nothing to do with one of my cars, but is a question from another forum i am a member of.

Thanks!
Andy

 

[michaelc80]

If it's really, really bad then the damage may have already been done, and no matter what you do you'll end up repairing it, new fluid or old.

I would for sure get the old fluid out of there to minimize any damage.

 

[rgl]

It's not a good situation if you do nothing, and may be a bad situation if you do something. Flushing is probably not a good idea because you don't want more crud floating about sticking in delicate places. However, dropping the pan and changing the filter only changes maybe a third of the fluid cause most of it is stuck in the torque converter. Then you would be adding only a few new quarts of fluid without any flushing. That's what I would do. Then if it drove ok for a week or two I would drain it again, maybe not changing the filter this time. If instead the thing blew up and died, well, that's life. Much better it do so while you're expecting it than when you're in the middle of nowhere.

The needing an overhaul soon after can be a number of things from the new fluid loosening old gunk that then gets caught in the valve body, or seals that were stopped up with gunk may now leak because they are being cleaned by the new fluid, etc. However, leaving the old fluid in there means the crud suspended in it is going round and round wearing the transmission, plus the additives of the fluid are probably depleted or burnt by now. Or it may die soon thereafter simply because it was going to die whether you changed the fluid or not.

 

[pitzel]

Ok guys, I keep hearing this myth, 'pan drops only change 1/3rd of the fluid'. Let me quote from the specs of my GM 4T60/440-T4 transaxle:

"Pan Removal and Replacement -- 5.75L"
"After Complete Overhaul -- 7.5L"

That's 77% of the fluid removed just doing a pan drop.

I suspect the number is far greater than 1/3rd of the fluid removed in a pan drop for most other cars and trucks as well.

After a second pan drop, only 5% of the original fluid remains, and after the third pan drop, 1%. 5 gallons of ATF for a triple pan drop is a lot cheaper than paying someone to do a T-Tech flush, and is what I would do, over the course of a couple weeks, if confronted with a transmission with really old fluid.

 

[Matt A.]

Heh...

That's doing an overhaul to the transmission housing/gears. Says NOTHING regarding the Torque Converter. (You can re-use them even after a rebuild of the trans gears and such...)

Most transmissions take around 15 quarts full of ATF...

 

[82DMC12]

quote:

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Heh...

That's doing an overhaul to the transmission housing/gears. Says NOTHING regarding the Torque Converter. (You can re-use them even after a rebuild of the trans gears and such...)

Most transmissions take around 15 quarts full of ATF...

---

Actually very few exceed 14 quarts. Most passenger cars start at around 8 or 9, and rarely more than 12. Some Toyotas as low as 7. heavy duty trucks I have seen take up to 20 quarts. by and large most vehicles are under 14 quarts. Check out the MOTOR Transmission Fluid Service Guide for exact numbers.

I work in the industry and the reason I am asking this question is because I had always learned that new fluid might clean deposits out of the transmission and stick up the valves and other moving parts, causing self destruction soon after. On another newsgroup I am in some supposed mechanics are saying that's not true and just go ahead and change it. the transmission will die if it was going to die or live longer if it wasn't. I just wanted to hear what the guys around here have to say.

Andy

 

[rgl]

It's hard for anyone to give a good all round answer because the situation you pose is so dire that anything can happen. It's like a 70 year old man that didn't take care of himself going to the hospital with about 3 different medical conditions and having to decide if he is going to get an operation or not.

BTW, I have both dropped the pan and drained the converter on my 4.6 F150, the converter fills a good part of a bucket.

 

[Big Jim]

I have flushed very dirty high milage transmissions many times with no ill effects. If the trans is still operating properly, there is a good chance that all will be OK.

Leaving really bad fluid is only a good idea if you are going to be getting rid of the car -- getting rid of it immediately.

At least that has been my experience.

 

[Logik]

What about a drain/refill multiple times (so you have all fresh fluid) plus a dose of Auto-Rx or Lube Control, or similar cleaning additive.

This would make the debris that get dislodged liquify, and wouldn't obstruct anything.

It's a sound theory, but I don't know if it works in practice.

 

[Pablo]

The basis of this theory in VERY brief terms is (and already stated by others), yes - sometimes a transmission will fail within days of a good flush for whatever mechanical/lack of maint. reason.

Is it the fault of the new fluid? Of course not. BUT - transmission shop owners will have a grumpy customer, demanding to be made whole. Hence, the start of "We refuse to flush nasty transmissions, because the may fail" thing.

 

[unDummy]

You will not cause damage changing the ATF.

You should also change the filter especially if the vehicle has some mileage. Cleaning of the pan magnets, if equipped, should also be done. New OEM type pan gaskets should also be used to prevent future leaks.
If the vehicle has a drainplug, it would be wise to perform the simple drain/refill regularly for long transmission life.

Most people with problem transmissions look toward the flush as a fix. This is where many problems start. A fluid change will not rebuild a transmission. A fluid change will allow the transmission to continue to operate the way it was before the ATF change.

Quality mechanics/transmission shops have learned to avoid the low profit flush, to at least minimally take the vehicle for a ride to make sure that the transmission is functioning normally, and to do a complete service including filter change/magnet cleaning.......Anything less is hackwork deserving the consumer lawsuit.

 

[keith]

I had a transmission once, in a used car I purchased, where the ATF was like old thick glue. The car had a drain bolt for the transmission, and I started to drain out a quart a week and replace with fresh ATF. My logic was that the new ATF, with fresh detergents, would potentially put even more cr*p into the fluid. So by only swapping a little fluid, you won't be getting too much new junk in the transmission. After a few months, you will have swapped out enough fluid so that the remaining fluid is cleaning up and a lot of junk will have been drained out. Then do a full flush, change the filters, clean the magnets, kick the cat, whatever.

It worked for me and the transmission kept on working. YMMV. If your transmission is already damaged, changing the fluid won't fix it but it might prolong it a little.

Of course, use the correct ATF (e.g. Mercon V, ATF+3/4, whatever the manufacturer specifies).

 

[Lumberg]

quote:

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Originally posted by pitzel:
Ok guys, I keep hearing this myth, 'pan drops only change 1/3rd of the fluid'. Let me quote from the specs of my GM 4T60/440-T4 transaxle:

"Pan Removal and Replacement -- 5.75L"
"After Complete Overhaul -- 7.5L"

That's 77% of the fluid removed just doing a pan drop.

I suspect the number is far greater than 1/3rd of the fluid removed in a pan drop for most other cars and trucks as well.

After a second pan drop, only 5% of the original fluid remains, and after the third pan drop, 1%. 5 gallons of ATF for a triple pan drop is a lot cheaper than paying someone to do a T-Tech flush, and is what I would do, over the course of a couple weeks, if confronted with a transmission with really old fluid.

---

Triple pan drop?

1st pan drop, you install a drain plug.

Then it becoem sa single pan-drop, double drain and refill.

 

[82DMC12]

quote:

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Quality mechanics/transmission shops have learned to avoid the low profit flush, to at least minimally take the vehicle for a ride to make sure that the transmission is functioning normally, and to do a complete service including filter change/magnet cleaning.......Anything less is hackwork deserving the consumer lawsuit.

---

Low profit? It's clear that a flush is more profitable than a pan drop/service. Much less labor time (especially pain in the butt auto's like on a Dodge Caravan w/ OEM silicone gaskets or GM HD trucks with frame crossmembers over the bolts), and usually a steeper price. 14 qts of Dex in a T-Tech vs. 6 qts for a pan (don't forget cost of gasket/filter, usually $10-$17 cost) is small change compared to the labor and mess saved.

Not only that but not all OEM's recommend changing the filter at every service interval. It's kind of unnecessary if you change it every 15K like some manufacturer's recommond on their severe maint. schedules.

Andy

 

[Tones]

quote:

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Originally posted by 82DMC12:
...i have heard from some people that if the fluid is pretty dark/burned, you will do more damage flushing the transmission fluid than if you just leave it alone. is this true? what is the reason? ...

---

From what I have seen, the culprit is varnish that has accumulated due to prolonged use of the the neglected fluid. Flushing can loosen up this varnish which can plug ports and valves, etc.

As Logik and others have pointed out, I think the correct way to approach this transmission is to do an AutoRX treatment to try to dissolve the varnish, using as directed, or gradually introducing new fluid with multiple drains and fills. Even then there are no guarantees.

 

[Rob Taggs]

Seen many folks go to the local Cottmans to get their transmissions flush and refilled without one complaint. Most commented on how much better the transmission operated after having it done. I'm just a poor farm boy, so I really don't have the money to have it done.

 

[[email protected]]

Let me just tell you what I did. I bought a trans pan for my 2002 Envoy (4L60E trans) with a drain plug. This way, since I have 67k miles, I am going to change the filter and whatever fluid I can (5 quarts?). Then a few days later, im going to drain the pan and refill. Then, one last time Im going to drain and refill. This should ensure that I will replace at least 95% of the fluid.

 

[loudist]

Sorry chris, but thats not accurate.
When you drain the pan you are changing out 30% (by your estimation). The new fluid blends with the old fluid, so the new fluid is diluted by 2/3.
Then you change out the pan fluid again you add 30% new fluid to that blend of 30/70% and so on.
3 pan fluid changes isn't going to change out 95% of the old fluid. It is more like 70% new, 30% old.

Find out how to drain the torque converter (should be simple) so you can do this while you have the pan off. You will get out most of the old fluid, so your fresh fluid is not as nearly contaminated.

 

[T-Keith]

I bought my 88 Lesabre with 210,000 miles. After buying it I drove it to the local gas station. The oil was ~2 quarts low and so was the transmission.

After topping them off I noticed that both were black. I doubt the transmission fluid had been changed in a very long time.

So here's what I did. Changed the fluid and flush the coolers. Added AutoRX and drove for 1000 miles. Changed the fluid and flush the coolers again, started and ran for several minutes and changed the fluid again.

It seems to shift great, no problems yet.

-T

 

[ediamiam]

Reading this board has probably saved the auto trans on my '93 Mazda 626 from my stupidity. I bought the car used at 95k, and got around to checking the transmission fluid at 140k. It was red/blackish - definitely not clear. I went to the dollar store and got a bunch of the citgo dex/mercon for $1 each, and did incremental 2 qt changes over the last couple of months. Also got some lubecontrol just this week and drop in a few oz with the latest incremental chg. Fluid is looking red again, and clear. Shifting definitely improved. Usually am more anal about this stuff, but never got around to it. Probably because the last couple of cars had manual transmissions. Another bitog testimonial.