change automatic transmission fluid

i have a 2004 chevy silverado with a 6.6L V8 turbocharged duramax diesel. i am not sure if i have the GM 5 speed transmission or the allison 5 speed. but i was wondering where the spinoff filter was located and if there was a filter in the pan in addition to the spinoff filter, also does it have a drainplug in the pan? any tips or tricks would help too. how would i tell which transmission my truck has without crawling under it? is there a way to completely change out all of the fluid without taking it to a shop for a purge. i also wouldnt want to disconnect the cooler line to run it out.

Thanks for the help in advance and sorry for the book!:2cents:

It has two filters,a spin on and one inside the pan.There is a drain plug on the pan,use a good 6 point 15mm socket.Change both filters and the pan gasket is a reusable pan gasket,do not throw the pan gasket away.I have done one so far on my father's 2002 GMC Dually with an 8.1 big block and a 5 speed Allison automatic transmission.The 8.1 big block and the duramax diesel have the Allison transmission behind it.The spin on/off filter is near the pan and is painted red.

It was my understanding that the "filter" inside the pan is nothing more than a screen to keep big chunks out of the pump in the event of a catastrophic failure. Perhaps I was misinformed?

You won't get all the fluid changed without the proper machine. Unless the fluid is clean enough that it doesn't need a flush, dont just change the fluid in the pan. The new fluid can dislodge old deposits and clog up or stick open parts of the valve body. Considering the price of a new transmission, it's worth the $150+ to do it right.

Do not ever use the Machine if you want very expensive transmission repair such as a valve body cleaning or a rebuild.I hear nothing but horror stories after a flush with the machine.I know a transmission shop that does rebuilds or a valve body cleaning because someone had their transmission flushed with the machine.With the machine,the transmission is back flushed and where does the dirt,crud go?In the valve body causing shifting problems resulting in sticky valves.The lines are above the valve body and the filter is below the valve body.The line flush is the better way,it gets rid of the dirt,crud out and you can see the condition of the fluid.

I agree line flushing prceedure is the way to clean out normal contamination usually found in transmissions that have no clutch on other metal contaminates. this proceedure takes more time, but is the correct way . even GM agrees...... its in the repair manual!

what is the procedure for flushing that you were talking about, would it work if i just changed the fluid in the pan the first time, then let it heat to normal temp. and drive it arround a little and then change the fluid in the pan again?

so... what is "the machine", and what's the "line flush". The flush I was refering to hooks up through one of the cooler lines. A cleaner is added and the car is driven (on the hoist) in all the gears for 15 min. Then, the valve on the machine is turned to "process", old fluid flows in, and the exact same ammount of new fluid comes out. I wasn't aware of one that back flushes it... although I'm sure it would be a mess. At the shop I work at, we have done several hundred flushes (probably getting close to 1,000) and not had a single comeback for any transmission issue.

If you change the fluid in the pan, the first time you will get around 50% new fluid. The next time 25%, then 12.5, 6.25, 3.125, etc. As long as the fluid is clean, a pan drain is probably ok. If it is even slightly dirty, I would do a flush.

I did a search and found this thread from earlier this year.

http://www.automotiveforums.com/vbulletin/t335129.html

Most people agreed a flush is the way to go. A few didn't, and still don't.

Of one my posts (close to the bottom), describes what the flush is and why to do it.

I know the owner of this transmission shop very well and my father has seen them do valve body cleanings becuase of a flush with the machine.The line flush is real easy,disconnect the bottom line on the radatior,put a hose on it and point it to a pan ot bucket.Have a box of transmission fluid on handStart pouring fluid in while running and make sure you do not run the transmission dry.Stop when it is clear,your done and reconnect the line to the radatior