coppercutlass

Stupid question but it's a legit one. I have a th400 that was ran behind an 11 sec car and my trans is on the fritz so that one is going in. I don't know what atf is in there so I would like to drain all of the fluid out. Anyone done this before . Should I be that worried or just top it off with multi use atf .

Magna86

Are you doing this before or after install? The correct way would be to do it when the transmission warm like you are supposed to do an oil change. It this case I wouldn't worry about about.


With that being said you stated your current trans is going out. I would be worried about getting the fluid out of the trans cooler because there could be debris that would go right into the TH400. Before removing the old trans I would remove the lower line(that return line I believe)start the vehicle and catch the fluid into a drain pan. You will have to add fluid to the trans as well so you dont starve it. Do this until you get about 2 quarts of fluid out as then the cooler should be good.

Support the trans off the floor
Remove the trans pan bolt except one in each corner
Loosen each corner bolt with drainpan underneath
Pan should start to come down but if not you have to break that"seal" using a screwdriver just be sure not to gouge the transpan surface
Seal broken fluid will start to come out remove 2 of the bolts so pan will hang and the majority of the fluid will drain into the drainpan
Remove last 2 bolts, trans pan and filter
Clean off the inside of trans with brakeclean and do the same with the trans pan and make sure to remove any old gasket or RTV from both surfaces.
Install filter and trans pan. Some kits will come with a gasket or you can just use red or black RTV to seal the pan against the trans.
I would install the trans empty and refill after all hooked up.
Trans will take Dexron V I belive is the number they are on now GM trans fluid.
Fill up the trans until the cold line on dipstick and start letting the fluid circulate/warm up and check for any immediate fluid drop before shifting trans.
With car on jack stands shift car into gear and let it free spin. Makesure you are pressing the break before you shift from R to D. When in D the car should shift thorugh the 3 gears on its own. Stop the wheels and then accelerate watching/feeling the car the car shifts.
Do this until the car is up to operating temperature and check the fluid level in park and add more if needed.

That pretty much sums it up.

coppercutlass

No im talking about like flushing my trans dry. I don't know what kind of fluid is in it. This is my back up th400 and I got it from a car I parted out . Dropping the pan will only do about 5 qts. I think the trans holds 12 to 13 total depending on converter. I was just wondering if I tipped the trans with the tail shaft toward the ground if it will all drain out .

coppercutlass

I think my question should have been how to flush a trans while it's off the car.

Magna86

It will probably have Dexron fluid in it and all of them are compatible so no worries if some if left to mix with the new stuff. The only way to completely get all the fluid out is to tear the trans apart. You can dump fluid out of the torque converter but wont get it all out. Don't think you will get anymore fluid out of it just by tipping it up than servicing it. Dump the convertor fluid, remove pan and filter, once drained tip towards rear and see if more fluid comes out, finish servicing trans as I said, install trans, fill with new fluid, disconnect cooler return line and start vehicle. Continue catching drain fluid out of the cooler until it comes out clean red like new fluid. Makesure not to starve the trans. Shut off top off and go through the steps to see how she shifts and warms up. That is your best bet to ge tas much of the fluid as you can without disassembling the trans. I would not install that trans without doing any less.

Nasty455

Its easier off the car...I stand the transmission on the bell housing and remove the pan bolts...clean the gasket replace the pan with one that includes a drain plug...you can then install a few bolts and let the trans sit over night to catch any fluid that got trapped when you tipped the transmission on its end.

coppercutlass

I have to take the pan off it leaked . a new filter wont kill it either . I just need to get most of the fluid out so I can put new fluid in. I was thinking the tail shaft because I have a small oil drum that's empty and the bell housing fits nice in there but I guess it does not matter which end it comes out of.

rustyroger

You will almost certainly have contaminants in the torque converter on your bad transmission which you will effectively never get completely out, I'm guessing you plan on changing the converter as well?.
If the transmission (& converter) came from an 11 second car it might not be good for street use.

Roger.

coppercutlass

The back up trans has a 10 in. 3000 stall. Currently im running a 10 in. 2800 stall Semi full manual forward pattern. Im not worried about it. My car is not a stocker the engine is pretty built up so to speak for an sbo.