Tranny Fluid Change.

[markjw]

I changed the transmission fluid on my "new to me" 1991 Legacy wagon. AWD,auto.

 

I just wanted to share a couple things here. I was at first gonna do the drain,fill,drain,fill method. But,I wanted to try something diffrent. So,I went and bought two 5 foot lenghts of clear,3/8" tubing.

 

I attached one piece of hose to the botton nipple on the Radiator tranny fluid cooling tank and,I attached the other piece of hose,by way of a short piece of copper tube,to the return hose that I pulled off the lower nipple.

 

The hose coming off the radiator nipple was pointed into a large catch container.

 

The hose attached to the return line was dunked into a new, very clean 3 gal. bucket filled with 8 qts. of fresh tranny fluid.

 

The idea was to start the car and let the old fluid pump out of the lower nipple on the cooling tank into the catch container,and the fresh fluid would be sucked into the tranny by the return line.

 

Well,it didn't work. The old fluid pumped out fine,but the fresh fluid wasn't being sucked in.Not at all. So,apparently,the tranny pump only pushes fluid into the top of the cooling tank, down thru the tank and continues to push the fluid into the return line and back into the tranny. There is no suction at all.

 

We realized this instantly,thanks to the clear tubing,and shut it down.

 

So,at this point,we just poured the fresh fluid into the dip stick hole,thru a long,narrow funnel,all while running the engine and pumping the old fluid into the catch container. It worked very well. Here's the interesting part.When the old fluid was done pumping out,the hose started to sputter air instead of fluid. We let this go on for a few seconds,then the tranny fluid started pumping out again,and, it was now pumping the fresh fluid.So,we shut it down.

 

We button'd all the hoses up,and ran the car for a few minutes,letting things settle out.In the end,we had to top off with another quart and a half to reach full/hot on the stick.

 

To summarize,If I was to do this again,I'd simply attach one lenght of 3/8" clear tube to the lower nipple,point that at a catch container,and, while running the car,pour fresh fluid into the dipstick hole until the solid stream of old fluid sputterd air. Re attach the lower return line to the nipple and top it off the correct way. Simple.

Edited January 13, 2010 by markjw

[ericem]

OR you can just remove the plug at the bottom of the pan, and refill?

[Olnick]

Thanks for the great writeup, markjw. That kind of thorough flush is something I've wanted to do to my wife's Maxima for years (but never had the guts to!!!)

[markjw]

OR you can just remove the plug at the bottom of the pan, and refill?

 

And,drive around and refill and drive around and refill and so on and so on. No thanks. In the end,your tranny still has old fluid in it.

 

This worked slick. When the flow of old fluid started to sputter air,the level in the catch container was just below the 2 gal. mark. And,we had managed to add about a gallon and a half of fresh fluid at that point. The tranny,I believe,never had a dangerously low amount of fluid in it. From start to finish with the business of pumping old fluid and adding new with the car running took no more than 3 minutes.

 

Here's a pic of the stuff I used. The bucket I found was already calibrated in 1 ounce increments up to 3 gal. I just hi-lighted with a sharpie to see better.

 

The plan was to make sure we didn't drain more than we were able to add. Easily done with a clearly marked catch container. If we were not able to keep up,we were gonna shut the car off. We never had to. I'm sure this has been done before,but I searched and searched the archives and couldn't find a thread that outlined the scarry part. Draining and adding at the same time.

 

The hose is 3/8"..fits perfect.

 

Also,the Subaru dealer quoted me $170 to flush the tranny. I managed to do this for about $45 in fluid and $6 in stuff. And,I know my tranny has new fluid in it and,nothing got messed up. Peace of mind is Priceless.

 

 

Edited January 13, 2010 by markjw

[lmdew]

I've done it this way for years. My only variation is I use a gallon plastic jug and when it's 3/4 full I shut down the engine and over fill the transmission again.

 

The reason you got air IMHO is you pumped fluid out faster than it was going in.

 

I get 4 gallons of fresh fluid, drain and fill the pan and then use the radiator hose to pump out the old fluid. It works great!

[johnceggleston]

what would happen if you hung a bucket with a bottom drain/tube and 10 qts of new fluid so gravity would work in your favor. would the new fluid flow in fast enough?

[bulwnkl]

Not likely, John. The pump pumps the fluid out quickly. I've used this method, too, though I just run the truck (Baja) until the pump sucks air, fill the tranny with fluid, and repeat once or twice more. I'll end up using a case (3 gallons in quarts) of tranny fluid, though the dark stuff is all gone after a couple gallons in this truck.

[markjw]

I know lots of folks use the pump method in one form or another. I read a ton of threads about tranny fluid drain and fill. In fact,I got the idea to use the tranny pump here,on the board. But,there is little written about what actually happens when you turn the engine on.

 

My first attempt at simply sucking the new fluid into the transmission with an extended,lower return hose,came from the board,here.But,this doesn't work. There is no "suction" in the lower hose. Only pressure in the top hose.

 

I have no idea why the transition from pumping old fluid to pumping fresh fluid was interupted with air sputtering,but,it didn't seem like a problem. It was obviously a indicator that it was time to stop the engine and finish off the fill with all the hoses connected properly to the radiator. And,there was nearly 8 qts. of old fluid in the catch container when the sputtering started.

 

I'm wondering why the drain,fill,drive around,drain,fill,drive around,drain fill method is the recommended process when this way seems so easy and thorough.

Edited January 13, 2010 by markjw

[johnceggleston]

how long does it take to pump out the old fluid??

 

how much pressure is the fluid under at the radiator during normal operation?

[markjw]

how long does it take to pump out the old fluid??

 

how much pressure is the fluid under at the radiator during normal operation?

 

Couldn't have been more than 3 minutes,total from the time we started the car till our bucket had 2 gallons of old fluid in it. As far as the actual pressure,I can only say that out of a 3/8" I/D hose,it was squirting a stream about two feet out if held level like a garden hose. Very manageable.

[CNY_Dave]

So what you need is a low-effort positive-displacement pump driven by the same exact pump running backwards, metering new fluid in at the exact rate old fluid is pumped out.

 

Could go in the return or in the fill hole.

 

Dave

[Twitch de la Brat]

Thank you MarkJW.

 

One quick question, did you have the car in gear, in park or neutral?

Gonna do this very thing with my sister's "new" 91 Lego LS Wagon. (Aka Zeh

Dume Vagon)

Gotta fix some hard shifting and some other minor tranny issues.

 

Twitch

[markjw]

We started the process in park,of course. But,about 30 seconds into the pumping,I had my wife run the tranny through the gears.Pausing at each one for just a few seconds,and then back into park. The shifting of the gears had no effect on the stream of fluid being displaced.

 

This was my brothers idea. Whether it is good or bad or has no effect,that's what we did. I've put about 4k miles on this car since the fluid change and the thing is running perfect.

[Twitch de la Brat]

Well, it worked.

It only took about 15 minutes to do

 

And it got rid of some of the problems she was having.

Still has torque bind :-\

But its gonna need to have the duty c solenoid changed.

No big deal.

 

Again, thanks for the tip!

 

Twitch