Auto tranny clutches are engaged with hydraulic clutches. As these clutches wear the worn particles either stay in the fluid or are filtered out. The transmission fluid is darkened by those clutch particles still in suspension. As time goes by the fluid is to some extent subject to shearing. The more it is sheared the more likely there is to be less pressure, which will mean more clutch wear and darker fluid. It is my contention that draining the tranny pan and refilling with fresh fluid will remove some portion of the worn clutch particles and increase the viscosity of the transmission fluid. This will keep the pressures high and reduce clutch wear. All of this should greatly increase the lifespan of the tranny. So, I believe just swapping fluid periodically is nearly as good as dropping the pan and changing fluid and filter, and is a lot easier and cheaper. Anyone agree or disagree???
ATF Changing Logic:
- Thread starter redbone3
- Start date
- Joined
- Feb 6, 2021
- Messages
- 1,410
If it has never been changed before and is used, cleaning the pan and replacing the filter is a good option first and then refilling.
If it is new, then swapping the fluid out periodically is a great solution, and you only have to change the filter every 100,000 miles.
If it is new, then swapping the fluid out periodically is a great solution, and you only have to change the filter every 100,000 miles.
Honda/Acura agrees with you as that is the only way they recommend you replace fluid in a lot of their transmissions.
I know someone smarter than myself could correct me, but I believe shift pressures are controlled by a variable relief valve or proportional pressure reducing valve with pressure feedback. That means the pressure should be pretty much the same for a given shift condition with little impact from fluid viscosity.
Again, I could be wrong on that!
Again, I could be wrong on that!
Agree and that's what I've been doing for years. I do a spill and fill about every 20,000 miles and have never (knock on wood) has a single transmission problem with over a million miles on the vehicles I've owned in the last 30 years. I'm not claiming doing spill and fills caused me to not have any transmission problems, but it sure didn't hurt anything.
My Hyundai doesn't really have a pan in the traditional sense, changing the filter requires the transaxle to be basically split in half.
gathermewool
Site Donor 2023
You mean you’ve never had to change an AT, right...because of the ATF changes???
Didn’t we already discuss this ad nauseum?
Goal for ATF drain and fills, when are you "satisfied?"
Doing drain and fills that will ultimately lead to a pan drop and filter replacement on a high mileage auto, which is a more involved job. But just attempting to get the fluid freshened up in the short term, since it's very simple and relatively mess-free with a Mityvac (excellent tool). I...
bobistheoilguy.com
I'm no engineer but I'm strongly in the camp of changing fluid, getting and keeping as much fresh fluid in it as possible in lieu of or in addition to a pan drop and filter replacement. Keeping fresh fluids is seems to me will extract some contaminants.
I'd guess that if you did a filter replacement every 50k to 100k miles, you'd be good. So in a typical vehicle with a 300k lifespan that's 5 changes. Not a lot to ask.
I'd guess that if you did a filter replacement every 50k to 100k miles, you'd be good. So in a typical vehicle with a 300k lifespan that's 5 changes. Not a lot to ask.
Its basically what we do with engine oil.... Just sayin.
NIce username... I'm a fan of the red bones
Yes, but the point I was making is that I have never changed the filter in any of my cars.
Not sure about neglected trans. If haven't been serviced for a long time, better leave it alone and wait for the time to come.
Just about every other day, no ?
- Joined
- Feb 6, 2021
- Messages
- 1,410
You are correct, there is a pump in the transmission pumping the fluid to pressure, but if its too thick then it will cause problems, due to flow rate, but almost all modern ATF slightly under 7 CsT or 7.2 CsT .
It’s more than just a pump.
There is a fluid pressure regulation system on most automatics. A solenoid, for example, that controls the line pressure, is common in many valve bodies.
There is a fluid pressure regulation system on most automatics. A solenoid, for example, that controls the line pressure, is common in many valve bodies.
That mechanism reduces pressure to some predetermined value. If the pump pressure is below that there is trouble in River City.
I pull and replace three quarts a year and yes the old Dexron 6 is always darker. However, I find the magnet in the pan is coated with particles when I drop the pan every 50,000 miles. I’ve opened up a tranny filter that was in use for 5 years and found only a few metal particles in it and nothing else. YRMV.
Last edited:
