Should I change my transmission fluid and filter?

[89 jimmy]

I’m debating on wether or not to change my transmission fluid and filter. 89 Jimmy, 700r4. I’m sure you’ve all heard the story’s about this. Many different opinions. My current fluid looks decent, it’s still red. I changed it last about 10 years ago and about 60-70,000 miles since. I do frequently tow my fishing boat (about 3,000lbs) often, up some hills, and sometimes very hot weather. I do have an added transmission cooler. What do you guys think? I would only be doing the drop pan and filter and not the complete flush. I really want to do it, but I’m scared of all the stories I’ve heard.

 

[obijuank5]

You know the history of it. It's when you do it as a hail Mary try to fix a delayed engagement then its guaranteed to shit the bed.
I'd do it more frequently but 60k ain't bad.

 

[89 jimmy]

I should also note that the transmission shifts fine now with no problems

 

[red EOD]

Changing the fluid and filter in the pan is necessary.

Flushing the system is what causes the problems with worn transmissions.

 

[Truckman4life]

I'd weld a pipe plug bung in the pan and that way you can just do a drain and fill every so often. That's what I do at work with our Super Duty trucks since they already have a factory drain fitting and the filters on them are pretty much just a screen that is big enough it will never get plugged.

 

[Greg Ducato]

Pan service or flush, Any service is better than no service at all. I am a fan of the system flush as it removes all fluids from the system and replaces them with all new fluids and this is the #1 objective of a transmission service, to remove that broken down, contaminated oil. Changing the filter is a bonus but not required, if you are choking a filter shut with debris you have real trans problems no service can reverse.

 

[6.2Blazer]

Assume you are talking about the urban legend that the transmission will fail if you change the fluid or flush the system. That simply does not make any sense......if the transmission does fail shortly after you change the fluid it just means the transmission was about ready to fail anyway. From my experience this myth comes from all the people who start having transmission problems and in desperation go and have the trans fluid flushed. A couple days later the trans goes completely out and they blame the flush for it, and not the fact the transmission was already trashed. Of the people I have talked to that have had the trans flushed probably 9 of 10 only did it because the transmission was already acting up, and with an automatic trans once it starts acting up there is rarely anything you can do to save it short of a rebuild.

 

[89 jimmy]

From what I’ve read it’s the detergents in the new fluid that will clean the dirt, sludge or whatever off of the parts. That dirt supposedly will clog passages and ultimately lead to failure especially in transmissions that have not had the fluid changed in many miles

 

[Truckman4life]

I don't like the flush jobs you get at quick lube type places because they usually contaminate with other fluids or debris or cause other damage doing the flush. If you do it yourself just pop off what ever trans cooler hose that is easily accessible and run the truck pumping the fluid out into a pan while simultaneously adding fluid to the trans til it comes out looking like new atf. Obviously you will use extra fluid and you would also have to have the pan on and new filter in first in order to run it.

 

[Greg Ducato]

From what I’ve read it’s the detergents in the new fluid that will clean the dirt, sludge or whatever off of the parts. That dirt supposedly will clog passages and ultimately lead to failure especially in transmissions that have not had the fluid changed in many miles

I hear that a lot as well but the truth is that any particulate in the system will usually find its way into the pan or filter and be captured. There are no passages small enough in an automatic trans to be clogged by a particulate small enough to make it through a filter. High mileage transmissions are actually the ones that a full flush stand the most to benefit as all of the fluid in the trans, converter and cooler system is evacuated and replaced.

 

[Greg Ducato]

I don't like the flush jobs you get at quick lube type places because they usually contaminate with other fluids or debris or cause other damage doing the flush. If you do it yourself just pop off what ever trans cooler hose that is easily accessible and run the truck pumping the fluid out into a pan while simultaneously adding fluid to the trans til it comes out looking like new atf. Obviously you will use extra fluid and you would also have to have the pan on and new filter in first in order to run it.

That is a good do-it-yourself alternative to paying for a flush. Most pro flush machines will push 16 qts of new ATF through a trans so I would use that as my minimum and be prepared to find a way to catch and dispose of all that fluid when you are finished. Professional flush machines are a closed system so there is no chance of contaminating the new fluids being introduced to the transmission during service.

 

[89 jimmy]

If I just drop the pan on the transmission and change the filter how many quarts of fluid would I need? I’m also going to do the transfer case fluid. How much fluid does that hold? About 2.5 quarts? (NP 241) Thx

 

[Greg Ducato]

Depending on how long you let it drain, anywhere from 4-6 qts on a filter change. The Transfer case will be about 2.25-2.5 qts, both Dexron II or better

 

[fordsucks!]

From my experience this myth comes from all the people who start having transmission problems and in desperation go and have the trans fluid flushed. A couple days later the trans goes completely out and they blame the flush for it, and not the fact the transmission was already trashed.

I won't lie, this has happened to me. A really bad towing session through the mountains caused tranny to act funny. Limped around a couple days. Went to get a flush, tranny grenaded the next day.

I have never gotten a flush since, and I've never blown a tranny since.

 

[Greg Ducato]

I won't lie, this has happened to me. A really bad towing session through the mountains caused tranny to act funny. Limped around a couple days. Went to get a flush, tranny grenaded the next day.

I have never gotten a flush since, and I've never blown a tranny since.

An experience like that can leave a bad taste in your mouth

 

[diesel4me]

My thoughts about flushing a transmission is it "might" cause an issue where none existed...not so much for dirt & debris being "loosened up" ,but the flushing machine itself,and the fluid in it--is it "recycled" fluid and simply filtered out and put back in,or is the new fluid separate from the stuff being sucked out ?..

I'm not familiar with them or how they work,but if they consist of a "closed loop" system that supposedly puts fresh fluid in while the old is being flushed ,how does the machine keep fluid from other vehicles it was used on from mixing in with the new fluid.?..

Seeing there is no less than a dozen various types of ATF and using the wrong one can cause issues or damage,I wonder how many transmissions needing dexron end up getting a mixture of various other fluids,due to some being left in the hoses and pump on the machine..

The most I've done to my automatics is drop the pan,replace the filter,make sure all the valve body bolts are tight,and put in the correct amount of the proper ATF and call it good..
I've found several loose bolts on a few TH350's and tightening them cured a delayed engagement after a cold start and whining noises on one car I had..I found several bolts in the pan on a K-10 Suburban I bought with a "blown tranny" ,after I put them back in and tightened them,it drove and shifted perfectly again!..

I'd have preferred to get rid of ALL the old fluid,but the method of removing the cooler line usually results in a massive gusher that's tough to control when your working alone,and you'd need like 20 quarts of fluid..which ain't exactly cheap nowadays..

I've been reading up on other forums about people who have been using tractor hydraulic/transmission fluid in older non-overdrive automatics like TH350's and TH400's,and they claim it reduces the stall speed of the converter some,and withstands higher heat better,and its basically the same thing as dexron without any dye to color it,some specs on it even say it can cover the uses where dexron is required....
Seeing you can get 5 gallon pails of it for about $25,its a lot cheaper than dexron,and farmers who live out in the boonies who used it when that was all they had handy,say their trucks haven't had any issues with the transmissions..even some racers use it exclusively instead of dexron..I've been tempted to try it,but I don't want to find out it wasn't good enough and ruin a transmission to save a few bucks on fluid..but if it IS better,its a bargain..

 

[6.2Blazer]

My thoughts about flushing a transmission is it "might" cause an issue where none existed...not so much for dirt & debris being "loosened up" ,but the flushing machine itself,and the fluid in it--is it "recycled" fluid and simply filtered out and put back in,or is the new fluid separate from the stuff being sucked out ?..

.

That is not how any true transmission flushing machines work that I have ever seen! There should be two separate tanks, one with new fluid and one to hold the old fluid. For every quart of new fluid you pump in you pump the same amount of old fluid out. You do not cycle random used fluid back through a transmission.......well, I guess if the shop was shady or just stupid and filled up the new fluid tank with waste fluid it could happen.

I know at one time Chrysler specified flushing mineral spirits through the transmission system until it ran clear, and then flushed it with new fluid.

Regarding a different post above about a flush knocking loose build up and debris and causing issues, sure that could happen but if you have a bunch of crap like that in a transmission already it is on it's already on the way out. It's the same thing of all these people who have a transmission grenade, then they just slap a new one in without flushing out the cooler lines and torque converter (which should be replaced anyway) and then the new transmission fails shortly after that. They call that trans junk even though the torque converter and cooler were packed with debris from the original trans grenading and runs through the new trans causing it to fail.

 

[6.2Blazer]

I won't lie, this has happened to me. A really bad towing session through the mountains caused tranny to act funny. Limped around a couple days. Went to get a flush, tranny grenaded the next day.

I have never gotten a flush since, and I've never blown a tranny since.

I know where you are coming from as it's hard to shake that feeling, but proves my point exactly. You say you have never had the trans flushed since and never blown tranny.......but on that same note have you ever had another "really bad towing session through the mountains that caused the tranny to act funny and limp around for a couple days"? Please don't get offensive and take this the wrong way, but if you hadn't flushed the tranny do you really think it would have not grenaded? If it was already acting funning and you were limping around what would you expect to happen otherwise?

 

[fordsucks!]

I know where you are coming from as it's hard to shake that feeling, but proves my point exactly. You say you have never had the trans flushed since and never blown tranny.......but on that same note have you ever had another "really bad towing session through the mountains that caused the tranny to act funny and limp around for a couple days"? Please don't get offensive and take this the wrong way, but if you hadn't flushed the tranny do you really think it would have not grenaded? If it was already acting funning and you were limping around what would you expect to happen otherwise?

My point exactly, I destroyed the tranny Towing but it's easier to point the finger at the oil change place.

 

[Jim burton]

It shouldn't be a problem for you to change it. Here's my two cents on the whole 'change it or not"...back in the 1900's I used to work at a few different auto shops. The story back then was that if you hadn't changed your transmission fluid in a long time...and the fluid was worn (not the transmission...the fluid)...it wasn't 'dirt' that gets dislodged that causes issues....rather, it's the accumulation of heat build up on the old transmission fluid that causes it to form a varnishlike substance in the passages. Changing the fluid reintroduces fresh fluid, with the appurtenant detergents, that REMOVE the varnish, as they were designed to keep from happening to begin with.
...and that was the 'shop knowledge' back in the late 1980's early 1990's. The fluids have changed so much since then, that I don't even know if the fluid even starts to form any kind of 'varnish'.
Even if you accept that varnished old burnt transmission fluid was the issue....you would have to have had a LOT of miles to wear your trans fluid out...or very very HARD miles....or a combination of the two... If you have an older mileage transmission (like 100,000 miles, no oil changes) and then you tow a 25' boat up the mountains and back....THAT'S the type of scenario where....you MIGHT be having an issue with the trans fluid change seeming to cause a failure. If you had changed the fluid prior to the boat pull, you MAY prevent the subsequent failure, but even still...that goes back to a transmission that had worn out fluid to begin with, which means the clutches would have been worn, etc etc.

Consequently, since you indicate that the trans fluid still appears decent, and it's not really high mileage....my bet would be that it should be fine. Also, you aren't changing all of the fluid....you'd still have some of the old fluid in teh converter, pump and lines...so doing a partial swap shouldn't present an issue anyway. If you're taking the pan off, for me, I would definetely change with one with a drain plug so that you can just drop the fluid every few oil changes so that you don't have to have that anxiety anymore...lolz.