Questions about the process(es) of changing automatic transmission fluid

Messages
494
Location
Washington DC area
We've all seen the threads debating what kind of ATF to use. Can we talk about how to change it? As far as I can tell, there are at least two methods:

  1. Multiple partial drain/refills: the most common DIY method where you drain about a third of the transmission at a time, top it up, start the car and run through the gears, rinse and repeat twice.
  2. A flush machine: this is a machine with a pump in it which connects to the lines leading from the transmission to the radiator. This machine essentially replaces the radiator in the loop and receives dirty fluid from the transmission and sends back fresh fluid from a pre-loaded resevoir. I'm told that these aren't the safest and can "bend fins inside the torque converter", Is this bro science? For the record, I have a Toyota 86 with a variant of the AISIN A960E.
  3. ???? I think I have seen people referring to a process that is DIY but also somehow uses the lines between the transmission and the radiator? Not sure
I'm personally interested in the full flush and replace, but what does one have to watch out for when you have a mechanic with the machine and you bring them the ATF to replace with?

Thanks,
Lumberg
 
Messages
16,124
Location
NE,Ohio
We've all seen the threads debating what kind of ATF to use. Can we talk about how to change it? As far as I can tell, there are at least two methods:

  1. Multiple partial drain/refills: the most common DIY method where you drain about a third of the transmission at a time, top it up, start the car and run through the gears, rinse and repeat twice.
  2. A flush machine: this is a machine with a pump in it which connects to the lines leading from the transmission to the radiator. This machine essentially replaces the radiator in the loop and receives dirty fluid from the transmission and sends back fresh fluid from a pre-loaded resevoir. I'm told that these aren't the safest and can "bend fins inside the torque converter", Is this bro science? For the record, I have a Toyota 86 with a variant of the AISIN A960E.
  3. ???? I think I have seen people referring to a process that is DIY but also somehow uses the lines between the transmission and the radiator? Not sure
I'm personally interested in the full flush and replace, but what does one have to watch out for when you have a mechanic with the machine and you bring them the ATF to replace with?

Thanks,
Lumberg
number 2 isnt quite correct, I've heard of those type
but the best type doesnt "forcefully pump" it back in. the dirty fluid goes into the machine and the pressure from the dirty fluid puts the same amount of clean fluid back into the transmission.


1. is easy mode I use it on 2002 accent, 2010 accent, 2020 elantra (in future) if you have a drain bolt on pan just drain it and refill.. just dont let it go 100k miles and no need to do multiple times.
I usually start around 50k-60k miles and drain and fill every 2 years.. for hyundais there is no replaceable trans filter.

I did 3 on my ford ranger among other vehicles. Disconnect trans cooler line attach clear tubing put in 5 gallon bucket marked for volume ie 1gal-2gal etc.
start truck, run until fluid sputters. shut off truck refill transmission. repeat

2, is ok but No need to do it really unless you are having someone else do the work.

Pan drop and filter replacement is important esp. first time to get all the initial break in debris out of the transmission. but not applicable to as many modern vehicles as it was in the past.
 
Messages
11,136
Location
MA
The standard factory recommended method is to drop the pan, clean the magnet and change the filter. Depending on the transmission, you don't get out all the fluid in the torque converter, maybe only about half. But that's what the factory knows when they recommend that method.
 
Messages
8,144
Location
MI
2.) Most, if not all of the "flush" machines are simply holding tanks for new and used fluid. The process uses the vehicle's transmission pump to exchange the fluid - the old fluid dumps into the one side of a reservoir. and new fluid is pushed into the system from the other side of the reservoir.
T Tech machine manual: http://jiffylubecs.gradepoint.com/en_us/doc/T-Tech_Manual.pdf

3.) Lots of discussion here about the cooler line "flush" (really exchange) method: https://www.google.com/search?q=coo...VoB50JHTz9CHEQrQIoBHoECAUQBQ&biw=1920&bih=966 .......Similar to the T Tech method, except you have to dump new fluid in manually.

A number of the new transmissions do not have a serviceable filter and pan removal is somewhat obsolete on them.
 
Last edited:
Messages
820
Location
Vancouver, BC Canada
Fluid exchanges are controversial because of potential ingress of dirt and because the fluid residue in the machine and lines contaminates the correct fluid for your transmission...or they try to get u to use a universal fluid. Mfr's almost all seem to prefer drop pan, clean pan + magnet(s), change filter, replenish fluid. Me, I'd give it mebe 200mi between drops... then do it three times total, filter change on whichever drop u prefer. Great if it has a drain plug...say drop and clean pan +change filter on the first go... then just drain thru drain plug thereafter.
 
Messages
820
Location
Vancouver, BC Canada
Can folks please help me understand one aspect of the "bucket/pour-in new fluid" method. You find the "return" line back into the transmission and direct it into a bucket while pouring in new fluid at approx the same rate... When you break the line going back in to the transmission (running it into a bucket) and run it like that for a little while, you have disconnected the lubricant supply point that the cooled ATF would normally supply. It obviously is a low pressure ATF supply point, but it is still a lube supply point. How can that be good for the transmission?
 
Messages
11,136
Location
MA
Can folks please help me understand one aspect of the "bucket/pour-in new fluid" method. You find the "return" line back into the transmission and direct it into a bucket while pouring in new fluid at approx the same rate... When you break the line going back in to the transmission (running it into a bucket) and run it like that for a little while, you have disconnected the lubricant supply point that the cooled ATF would normally supply. It obviously is a low pressure ATF supply point, but it is still a lube supply point. How can that be good for the transmission?
Usually it's only a short period. A little too OCD for me, I just prefer the pan drop method and call it a day. Normally you just run the car until the fluid stops and then top it afterwards. Doesn't really run long when the fluid stops and in theory does nothing to the car, it's not like it's in gear.
 
Messages
453
Location
kansas
Rundown of what i usually do:
drop pan and replace filter if possible (or just pull drain plug when applicable)
fill pan with whatever amount came out
pull a cooler line and perform an exchange 2 quarts at a time
 

Lumberg

Thread starter
Messages
494
Location
Washington DC area
Thanks for all the responses, guys. I've done the DIY cooler line thing, I always wondered if running until it sputters is bad.

Also thanks for clarifying that the fluid exchange machine uses the car's own trans pump to do the work.

Some background on why I ask: I take my car to the track and after about 10 track days the car is shifting at way too high of an RPM. This means that all the fluid is degraded so I want to flush it entirely because all the stuff that's in there now is bad.

In future I would consider partial changes as routine maintenance, but this time I need to exchange it as completely as possible.
 

Lumberg

Thread starter
Messages
494
Location
Washington DC area
2.) Most, if not all of the "flush" machines are simply holding tanks for new and used fluid. The process uses the vehicle's transmission pump to exchange the fluid - the old fluid dumps into the one side of a reservoir. and new fluid is pushed into the system from the other side of the reservoir.
T Tech machine manual: http://jiffylubecs.gradepoint.com/en_us/doc/T-Tech_Manual.pdf

3.) Lots of discussion here about the cooler line "flush" (really exchange) method: https://www.google.com/search?q=coo...VoB50JHTz9CHEQrQIoBHoECAUQBQ&biw=1920&bih=966 .......Similar to the T Tech method, except you have to dump new fluid in manually.

A number of the new transmissions do not have a serviceable filter and pan removal is somewhat obsolete on them.

Thank you, that second search link is 👌
 
Messages
5,757
Location
Fort Worth, Texas
Can folks please help me understand one aspect of the "bucket/pour-in new fluid" method. You find the "return" line back into the transmission and direct it into a bucket while pouring in new fluid at approx the same rate... When you break the line going back in to the transmission (running it into a bucket) and run it like that for a little while, you have disconnected the lubricant supply point that the cooled ATF would normally supply. It obviously is a low pressure ATF supply point, but it is still a lube supply point. How can that be good for the transmission?
The geartrain is stationary & doesn't need lubrication.
 
Messages
1,336
Location
Ontario, Canada
We've all seen the threads debating what kind of ATF to use. Can we talk about how to change it? As far as I can tell, there are at least two methods:

  1. Multiple partial drain/refills: the most common DIY method where you drain about a third of the transmission at a time, top it up, start the car and run through the gears, rinse and repeat twice.
  2. A flush machine: this is a machine with a pump in it which connects to the lines leading from the transmission to the radiator. This machine essentially replaces the radiator in the loop and receives dirty fluid from the transmission and sends back fresh fluid from a pre-loaded resevoir. I'm told that these aren't the safest and can "bend fins inside the torque converter", Is this bro science? For the record, I have a Toyota 86 with a variant of the AISIN A960E.
  3. ???? I think I have seen people referring to a process that is DIY but also somehow uses the lines between the transmission and the radiator? Not sure
I'm personally interested in the full flush and replace, but what does one have to watch out for when you have a mechanic with the machine and you bring them the ATF to replace with?

Thanks,
Lumberg
There is NO WAY that a fluid exchange machine can bend fins in te TC as it operates off the car battery so it only has enough power to push fluid through. This is my preferred method.
 
Messages
2,082
Location
North Carolina
One thing to add if you are doing the fluid exchange method. Some vehicles, like the new GM trucks, have a thermostat. So you have to bypass it.
 
Messages
2,839
Location
Caldwell Idaho
"I am sure we don't know how a auto trans lube and torque converter and control oil circuits work" Quote means not a negative on Clineberger's obvious skills ! but as a [we ] in the multitude of posts on this subject , do not know how the hydraulics of a trans works.
 

Lumberg

Thread starter
Messages
494
Location
Washington DC area
Today I took my car to the shop and had the transmission completely flushed with fluid I brought using a BG trans flush machine.

It worked like this:
  1. Hook up machine to trans cooling circuit. Simply patch in to the flow, so the cooler gets flushed out, too.
  2. Put machine on bypass mode and start car. Allow trans fluid to heat up (see thermostat comment above)
  3. Flick switch from bypass to flush. Observe flow rate (seemed to be steady at 1 gal/min).
  4. Sight glass/flow rate meter gradually turns clear
  5. Machine detects it has pushed the whole "charge" of fresh fluid through the transmission and drops its flow.
  6. Turn off car
  7. Disconnect lines and reconnect cooling circuit
  8. Start car
  9. Check overflow plug for fullness; add/remove fluid as necessary
  10. Put everything back together and test drive

I have a follow up question. I plan do do it the DIY way next time (unhook cooling line and dump into bucket). When I observed the BG machine, it showed a steady 1 gal/min which means you'd have two minutes until the trans ran dry (7.9 qt capacity). That's pretty good. But there was a spring inside that sight glass. Is it possible that the flow was being controlled by the spring, and I shouldn't assume a 1 gal/min flow rate from the car's internal transmission pump at idle?
 
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