How does the AT plumbing work?

[wahed3001]

Okay, so I know that just draining and refilling only changes about half the tranny fluid since the rest of it is inside the torque converter. But what happens to the fluid being refilled through the dipstick? Does it go straight to the pan or does some of it go to the torque converter and pushes some of the fluid in there out to the pan? If it's the second case then I can flush out the torque converter as well by filling through the dipstick while keeping the pan bolt off.

[toyomoho]

The dipstick drains straight to the trans pan. The fluid is pulled up from the pan into the trans/torque converter then cycled back to the pan. If you drain and refill the trans pan 3 to 4 times over a period of 50 miles you should removed most of the oil fluid from the trans.

You can also drain and overfill the pan with fluid, then disconnect the trans fluid oil cooler line that goes back to the pan. The trans pump will force the oil out (attach the hose to a large container). When the fluid stops coming out, stop the engine and refill the trans pan and repeat operation until clear fluid comes out. The trans holds 6-8 quarts, thus make sure you have a large container.

[wahed3001]

Originally Posted by toyomoho

The dipstick drains straight to the trans pan. The fluid is pulled up from the pan into the trans/torque converter then cycled back to the pan. If you drain and refill the trans pan 3 to 4 times over a period of 50 miles you should removed most of the oil fluid from the trans.

You can also drain and overfill the pan with fluid, then disconnect the trans fluid oil cooler line that goes back to the pan. The trans pump will force the oil out (attach the hose to a large container). When the fluid stops coming out, stop the engine and refill the trans pan and repeat operation until clear fluid comes out. The trans holds 6-8 quarts, thus make sure you have a large container.

Thanks for the info. One more question: When I install a new gasket on the transmission pan, do I need to apply any sealant such as weatherstrip cement?

[dc_98_cam]

Originally Posted by wahed3001

Thanks for the info. One more question: When I install a new gasket on the transmission pan, do I need to apply any sealant such as weatherstrip cement?

The negative factor with sealant is that some of it might come off inside the pan and clog the filter/strainer. ... Not really likely .... but possible.
I did not use any sealer ... I used an OEM gasket from the dealer .... $18 or so.
No problems or leaks ... Just be patient with the multiple pan bolts. Tighten each bolt partially ... and repeat going around the entire bolt pattern several times.
Recommended final bolt torque is something like 5 ft-lb.

Also, take a few minutes and clean out any sludge or debris in the bottom of the transmission pan. ...You could remove the strainer and rinse, also.

[eurohazard]

I used an aftermarket gasket and no sealant...works great no leaks here either. If you're going to change the fluid and remove the pan...might as well change the ATF filter too for a dollars.