How to: Flush your transmission on a GMT800 GM truck

ScottyBoy

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Today, I flushed my transmission to replace ALL of the fluid, not just the 5 quarts that is in the pan. Here is the basic rundown:
You'll need 12 quarts of Transmission fluid
One Transmisson cooler line fitting with a hose barb. I found one at O'Reilly's for 5 bucks.
DSC02229.jpg

You'll also need some clear tubing to connect to the barb fitting and run down to a bucket. I found some 3/8 inch clear tubing at Lowe's for 25 cents a foot. I used 6 feet to go from the barb to my bucket.
First, you'll need to drain the fluid from the pan and change the filter and pan gasket. Instructions for that portion can be found HERE.
Next, after you get the pan and everything reinstalled fill it with 4 quarts of transmission fluid. I used Cstrol Dexron VI. You'll need either a transmission funnel or a hose that screws right onto the bottle (which is what I did).
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Now once you get it filled with 4 quarts, now install your barb fitting to the radiotor. Undo the top transmission cooler line from the radiator and screw in the barb fitting in its place. Then connect your clear tubing to the hose barb and run it down to your bucket. Now this next step, its very helpful if you have a sceond person to help you. You need to start the engine and let it run for a few minutes. You'll see the fluid pump thru the clear tubing and down into your bucket.
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Once you start seeing air bubbles in the fluid going thru the tubing shut the engine off immediately. Thats why its helpful to have a helper in the driver's seat.
Now fill the transmission with 4 more quarts and repeat the flush procedure till you see air again. Then do it a third time with your remaining 4 quarts of fluid. Start it one more time and you should now see pure clean fluid running thru the tube.
DSC02221.jpg

Shut off the engine and disconnect the barb fitting and reconnect your trans cooler line. Check your fluid level with the dipstick and add more if needed. You have now replaced ALL of your transmission fluid including all the fluid in the torque converter and the transmission cooler. Drive it for at least 5 to 10 miles to get it warmed up, then check the fluid level again. Add more if needed. :cheers:
 

ScottyBoy

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Thanks Nick. :thumbs: Your write up made the filter and pan gasket portion of this that much easier for me. :cheers:
 

Bigredmariner

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Damn nice job Scott, I am gonna be doing this myself in a week or so. Your write up will help answer a few questions I had, thanks brother.:thumbs:
 

ScottyBoy

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Damn nice job Scott, I am gonna be doing this myself in a week or so. Your write up will help answer a few questions I had, thanks brother.:thumbs:

I strongly reccomend you get some Amsoil from Nick. I wish I did.:fume: I wanted to get this done ASAP though as I'm traveling in 2 more days down to south Louisiana to meet up with Justin. :thumbs:So I couldn't wait on the Amsoil to be shipped. For what the Castrol Dexron VI costs, the Amsoil isn't much more. And you have a 2006, so you have to use the Dexron VI in your truck, Jarrod.
 

Bigredmariner

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Damn nice job Scott, I am gonna be doing this myself in a week or so. Your write up will help answer a few questions I had, thanks brother.:thumbs:

I strongly reccomend you get some Amsoil from Nick. I wish I did.:fume: I wanted to get this done ASAP though as I'm traveling in 2 more days down to south Louisiana to meet up with Justin. :thumbs:So I couldn't wait on the Amsoil to be shipped. For what the Castrol Dexron VI costs, the Amsoil isn't much more. And you have a 2006, so you have to use the Dexron VI in your truck, Jarrod.
Yep I have 14 quarts and a filter ordered through Nick. I will be doing mine in a week or so when I get a chance.:thumbs:
 

ScottyBoy

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Damn nice job Scott, I am gonna be doing this myself in a week or so. Your write up will help answer a few questions I had, thanks brother.:thumbs:

I strongly reccomend you get some Amsoil from Nick. I wish I did.:fume: I wanted to get this done ASAP though as I'm traveling in 2 more days down to south Louisiana to meet up with Justin. :thumbs:So I couldn't wait on the Amsoil to be shipped. For what the Castrol Dexron VI costs, the Amsoil isn't much more. And you have a 2006, so you have to use the Dexron VI in your truck, Jarrod.
Yep I have 14 quarts and a filter ordered through Nick. I will be doing mine in a week or so when I get a chance.:thumbs:

I wish I would have thought to order mine early enough so I could have had it this weekend. :facepalm: So I guess all you need now is the barb fitting and some clear tubing and you are good to go. :thumbs:I found mine on the rack with all the nuts and bolts and door panel fasteners and stuff at my local O'Riellys. You can even write down the part number from the pic I posted to make sure you get the right fitting.
 

Bigredmariner

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I'll have to look into mine a bit, I think mine has those quick connect lines. Don't remember for sure but I will look into it this week if I get a chance. If it does have the threaded ones like you have I'll get that number from your pic.
 

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