What is the danger of changing HM ATF?

[RegDunlop]

I always hear people say you shouldnt touch the ATF on a High Mileage car as it could cause pieces that are being held together by gunk to become dislodged and then break something ( or some other explanation that is similar to that).

Anybody have an opinion on this.

I know the usual answer is that the transmission is on the way out, which causes people to finally change teir ATF, and then the inevitabkl [censored] out of said transmission happens anyway so it wasnt the fluid change that did it. I understand that .


But I mean a car that is running smoothly, no hard shifting , no stuttering, no slipping, no signs of a bad transmission.

 

[ARB1977]

If the fluid isn't burnt I don't see a problem. I would do a pan drop for a few changes vs doing a complete flush.

 

[qdeezie]

I've changed burnt fluid on plenty of vehicles that have never been changed before and the transmission did not die. Worst case scenario, another change within 5K to 10K miles afterwards would be a good idea to change it again just to get the residual buildup out of it if there are any concerns.

 

[scurvy]

Originally Posted By: RegDunlop
I always hear people say you shouldnt touch the ATF on a High Mileage car as it could cause pieces that are being held together by gunk to become dislodged and then break something ( or some other explanation that is similar to that)


Urban legend. Fear, Uncertainty, Doubt. Spurious. Lies!

You'll do more damage by not changing the fluid than you will from changing the fluid.

 

[Stelth]

I'm not sure. I recently changed the fluid in a 95 F-150, which admittedly was a little clunky going into reverse. Forward gears were OK. I lost reverse about 50' after backing off the ramps. Did another fluid change and lost third gear. Transmission shops say the tranny is toast.

This transmission had over 260,000 miles on it, and at least 135,000 of those were on the same fluid.

So this was probably one of those trannys that was "dead but didn't know it." I probably could have gotten a few thousand more miles out of it if I hadn't changed the fluid.

 

[Astro14]

I've heard stories like the one Stelth experienced...But I have not experienced it first hand. Bought a used Volvo from a bud, who had been religious on oil, but not ATF. Flushed it with fresh fluid at 140,000 - old fluid was almost black.

Tranny worked fine for 45,000 after that (until the car was totalled...)

 

[Letter_K]

Originally Posted By: qdeezie
Worst case scenario, another change within 5K to 10K miles afterwards would be a good idea to change it again just to get the residual buildup out of it if there are any concerns.


+1 Definitely a good idea if the fluid is really old and/or burnt. ALWAYS change the filter. Even Amsoil has a bulletin on their site that mentions changing the fluid and filter again when changing really old fluid.

Quote:
On relatively high mileage transmissions that have not been serviced in some time. One reason for this is that the sludge and dirt buildup within the transmission will not completely be removed during the service. When the new fluid (which has detergent properties) is placed in the transmission, over days and weeks, the internal components begin to wash the insides of the transmission.

This sludge does finally work loose and settles in the transmission filter, clogging it up even further than it may have been before service. In these extreme cases, where service has not been performed in some time, changing the filter may not completely fix the problem. Some mechanics recommend a second service a few weeks after the first, replacing the filter again, which may be partially clogged due to the cleaning
process in the transmission.


http://www.amsoil.com/lit/filter_man_council01.pdf

 

[440Magnum]

I have very strong opinions on that:

1) I don't believe its a common occurrence at all
2) If it DOES happen (a transmission fails because of fresh fluid) then it was already failed and you just didn't know it. In other words, it was a ticking time bomb. I'd rather know for sure than leave gunky fluid in there and hope for the best.

 

[Quest]

must change fluid, regardless.

Urban legend calls for a failing transmission + fluid change will not make things better, and the owner or mech will blame the fluid change as the cause of it (they can't even properly identify the cause and the consequence to that).

Bottomline: routine ATF fluid change should be performed religiously. Anything else are all urban legend and it's related to your transmission design (faulty transmission will fail sooner, regardless or not you keep your original ATF or change it regularly).

Q;

 

[SuperDave456]

I had the transmission serviced on my 2002 Ford Taurus when it had 98,000 miles on the original fluid.
I learned how to do it myself and did it again at 160,000 miles.
No problems.

I did my little sister's Taurus transmission, a 2001 I think, with 135,000 miles (i think) on the original fluid.
No problems.

I really like Mobil 1 multivehicle ATF, and Valvoline Maxlife Dex/Merc ATF.
I also add a bottle of Lubegard Red to just about everything I touch these days.

If your transmission is going to grenade, it is going to grenade nothing you can really do about it.
If your transmission has old fluid and you change it out you will probably be extending its life, in my opinion that chance at extra life is worth the $50-$60 in parts and a couple hours of labor.
If it dies, you start over and replace fluids and filters in a timely manner and try to squeeze as much life out of it as possible.
Transmission services beat the heck out of car payments, that's for sure.

 

[HTSS_TR]

Some shops don't want to change the high mileage ATF that never changed before, because they don't want to get blamed for its failure a short time later. But if you do it yourself then any time is better than never.

 

[Stelth]

What happened to me is not an urban legend. Tranny was working more-or-less OK, I changed the fluid and it died. This is two weeks ago.

This failure was caused by neglect, not by new transmission fluid, but changing the fluid hastened the end.

 

[440Magnum]

Originally Posted By: Stelth
What happened to me is not an urban legend. Tranny was working more-or-less OK, I changed the fluid and it died. This is two weeks ago.

This failure was caused by neglect, not by new transmission fluid, but changing the fluid hastened the end.


Or didn't. Correlation doesn't imply causation, coincidences do happen. I don't think you can say either way in this case. What actually failed in the transmission? Did it fail because of new fluid, or did it fail because of having to pump all the air out from the fluid change, or did it just happen to fail right after a fluid change?

 

[Stelth]

Originally Posted By: 440Magnum
Originally Posted By: Stelth
What happened to me is not an urban legend. Tranny was working more-or-less OK, I changed the fluid and it died. This is two weeks ago.

This failure was caused by neglect, not by new transmission fluid, but changing the fluid hastened the end.


Or didn't. Correlation doesn't imply causation, coincidences do happen. I don't think you can say either way in this case. What actually failed in the transmission? Did it fail because of new fluid, or did it fail because of having to pump all the air out from the fluid change, or did it just happen to fail right after a fluid change?


Well, I believe correlation does imply causation in this case. This is not the first time I've changed trans. fluid, and I haven't had this before.

I'm not testifying in court here. What happened happened, and you can make whatever conclusions you like. If you want to believe that it was just a coincidence, that's cool with me. I'm not going to try to change your mind.

OTOH, I'm convinced that if I had left it alone, it would have lasted longer. I don't know if "longer" would be a week or six months, but I'm convinced that changing the fluid was the straw that broke the camel's back in this case.

 

[Letter_K]

Originally Posted By: SuperDave456
I also add a bottle of Lubegard Red to just about everything I touch these days.


Ever tried Lubegard's tranny flush product? I'm tempted to use it before replacing with the Mobil 1 ATF and adding a bottle of Lubegard Red to finish off the flush.

The instruction mention running the flush for 5-10 minutes while on the lift, but the tech person I talked to at Lubegard said it would be fine to drive it instead. The FAQ says if you leave some flush in by doing a pan drop and refill it won't harm anything so I can't imagine driving it would cause a problem. I'm planning on pulling the cooler lines.

 

[440Magnum]

Originally Posted By: Stelth

OTOH, I'm convinced that if I had left it alone, it would have lasted longer. I don't know if "longer" would be a week or six months,


That's really my only point- you just don't KNOW. The correlation gives a fairly good hint that changing the fluid triggered *something,* but the claim that it "breaks crud loose that was making things work" isn't the only possibility. You said the transmission was already shifting badly. It was dead before the old fluid came out, for all intents an purposes.

 

[Letter_K]

Originally Posted By: 440Magnum
Originally Posted By: Stelth

OTOH, I'm convinced that if I had left it alone, it would have lasted longer. I don't know if "longer" would be a week or six months,


That's really my only point- you just don't KNOW. The correlation gives a fairly good hint that changing the fluid triggered *something,* but the claim that it "breaks crud loose that was making things work" isn't the only possibility. You said the transmission was already shifting badly. It was dead before the old fluid came out, for all intents an purposes.


Correct - I would think it is more likely the new fluid might have dissolved some varnish and containment that was holding together something. Perhaps a seal went bad and the gunk held it in place or something plugged up. It's all speculation on what caused the failure.

It was most likely on its last legs as the original poster mentioned it was having problems. Unfortunately, transmission problems are expensive and most shops just want to replace the whole unit. It would be worthwhile to tear into the thing and find out the cause of the failure, but it's $500 just to look cross-eyed at a transmission.

 

[Stelth]

Quote:
You said the transmission was already shifting badly. It was dead before the old fluid came out, for all intents an purposes.


Since I already said that (or words very similar), we are in total agreement on this point.

 

[440Magnum]

Originally Posted By: Letter_K


Correct - I would think it is more likely the new fluid might have dissolved some varnish and containment that was holding together something. Perhaps a seal went bad and the gunk held it in place or something plugged up. It's all speculation on what caused the failure.


Yes, it is indeed all speculation, but I have a different one. When a failure happens right after a fluid change, I tend to suspect that its the process of purging all the air out of the clutches and actuators that causes the failure. When the pump is blowing the air out, you get the equivalent of "water hammer" in home plumbing when the last of the air goes out and solid fluid pressure hits everything. The fact that people tend to rev the engine in neutral to speed the process probably doesn't help Old seals can be as hard as dry pasta, and my GUESS (yes, that's all it is) is that the pressure pulses crack the old rubber seals. The last transmission I rebuilt myself had a front clutch actuator seal that felt like ceramic instead of rubber, and it was cracked 2/3 of the way around the circumference.

Originally Posted By: Letter_K
Unfortunately, transmission problems are expensive and most shops just want to replace the whole unit.


I haven't had that experience yet, but then my last tranny rebuild was about 7-8 years ago. The shop re-worked the whole thing in-house, and added a few upgrades to address known weak spots (it was a 1993 Chrysler 42LE).

 

[Letter_K]

Originally Posted By: 440Magnum
Originally Posted By: Letter_K


Correct - I would think it is more likely the new fluid might have dissolved some varnish and containment that was holding together something. Perhaps a seal went bad and the gunk held it in place or something plugged up. It's all speculation on what caused the failure.


Yes, it is indeed all speculation, but I have a different one. When a failure happens right after a fluid change, I tend to suspect that its the process of purging all the air out of the clutches and actuators that causes the failure. When the pump is blowing the air out, you get the equivalent of "water hammer" in home plumbing when the last of the air goes out and solid fluid pressure hits everything. The fact that people tend to rev the engine in neutral to speed the process probably doesn't help Old seals can be as hard as dry pasta, and my GUESS (yes, that's all it is) is that the pressure pulses crack the old rubber seals. The last transmission I rebuilt myself had a front clutch actuator seal that felt like ceramic instead of rubber, and it was cracked 2/3 of the way around the circumference.

Originally Posted By: Letter_K
Unfortunately, transmission problems are expensive and most shops just want to replace the whole unit.


I haven't had that experience yet, but then my last tranny rebuild was about 7-8 years ago. The shop re-worked the whole thing in-house, and added a few upgrades to address known weak spots (it was a 1993 Chrysler 42LE).


Your idea sounds reasonable as a reason for a failure. I think we all know that a fluid change is for the better and the tranmission is on it's way out if a fluid change kills it. The fluid should be changed, but there is always that slight chance user error or something with the fluid/process may cause a problem. However, the chance of a complete failure is probably minimal unless you already have clear indication something is majorly wrong with the transmission.

I'm very cautious about doing a cooler flush that drains the pan completely. I'm almost more willing to go 2 quarts at a time so avoid getting the pan completely empty, but that makes it hard to shift through the circuit and make sure it is completely flushed. Any thoughts?

I think I had that same transmission in my 96 Intrepid and that was the car that put the fear of a transmission failure in the back of my head. You were luckier with your shop. I was in limp mode and the car had enough life that if was worth changing the transmission. I made the decision to replace the transmission and less than 2 years later I ran into problems with the replacement. Hard shifting when hot and fourth gear that wouldn't come unless I backed off the throttle completely and pressed it again.