Flush Or Change The Fluid In Tranny
 

I need to change the fluid in my Blazer. Is flushing a good way to go?

What do you mean by "flushing"?

I'm not a fan of flushing for at least 2 major reasons.

1. You don't know what is in the flush machine from a previous vehicle that could end up in your transmission.
2. You are not changing the filter as well, so what's the point in leaving particles there and adding new fluid?


Aside from the 2-4 quarts that remain in the torque converter (depends on how much remains in after you let it sit a while) you are changing most of the fluid as well as the filter if you drop the pan.

The truck should be driven 12-20 miles to warm the transmission fluid before the pan is removed.
The fluid should be drained while the transmission is warm.If you do so, most of the fluid will be drained out.

Here's how to change the fluid (and filter):




The truck should be driven 12-20 miles to warm the transmission fluid before the pan is removed.
The fluid should be drained while the transmission is warm.

1. Raise and support the front of the vehicle safely using jackstands.
2. Place a drain pan under the transmission housing and fluid pan.
3. Remove the pan bolts from the front and the sides, then loosen the rear bolts 4 turns.

I don't know what Blazer you have, but on some, it may be necessary to support the transmission tailshaft and remove the crossmember just behind the transmission for pan clearance or access to the pan bolts.

1. Using a small pry bar, carefully pry the pan downward at the front of the transmission. This will allow the pan to partially drain. Remove the remaining pan bolts and lower the pan from the transmission. Remove the screen and the filter from the valve body. Most screens are retained using a fastener; though some may use an interference fit between the screen tube and valve body.

If the transmission fluid is dark or has a burnt smell, transmission damage is indicated. Have the transmission checked professionally.
If the pan sticks, carefully tap sideways on the pan with a rubber or plastic mallet to break it loose; DO NOT dent the pan.
Empty the transmission pan of the remaining fluid, then remove the gasket material and clean with a solvent, then using a putty knife, carefully clean the gasket mounting surfaces.


To install:
1-Install a new filter using a new gasket or O-ring. If your transmission uses a filter equipped with a fully exposed screen, it may be cleaned and reused.


2-Use a new gasket and sealant and install the transmission pan. Install and tighten the retaining bolts to 8 ft. lbs. (11 Nm) using a criss-cross pattern.


3-Remove the jackstands and carefully lower the vehicle.


4-IMMEDIATELY refill the transmission housing with automatic transmission fluid. Add the fluid through the filler tube. (Don't overfill it)



5-With the gearshift lever in PARK, start the engine and let it idle. DO NOT race the engine.


6-Apply the parking brake and move the gearshift lever through each position. Return the lever to Park and check the fluid level with the engine idling. The level should be between the two dimples on the dipstick, about 1 / 4 in. (6mm) below the ADD mark. Add fluid, if necessary.


7-Check the fluid level after the truck has been driven enough to thoroughly warm the transmission.

You can hook up the trans cooler line to a hose and place it in a large 20+ qrt pan/bucket/drum and run the car at idle to drain the transmission. As soon as the line goes dry or even starts to show signs of sputter kill the motor right away. Then you can drop the pan without a mess. (If you even want to I rarely do as most of the modern transmissions these days just have a screen to replace and due to the pan magnet they rarely have any debris) Next make sure to turn the motor by hand (may be smart to disconect battery of course) to align the torque convertors drain plug to the acces hole and drain the TQ. Refill and run it thru the gears and check level.

Some great posts on how to do it. Here is a not so good way but is super easy. It is not so good as the filter does not get changed.

Go to Wal Mart ans purchase 16 quarts of Dextron VI, the advaned fluid for our trannies. Only buy at Wal Mart because it is 3.77 a quart, AuoZOn and Advance Auto are 5.99 a quart.

Go to hardware store and purchase 30 feet of clear tubing, likely 3/8". Cut it in half.Stick the tubing into your tranny dipstic and siphone it out it a large pan. This can take abut two hours, just go do something else. Measure the amount of fluid removed and replace with the Dextron VI. Drive for a few days and repeat process.

The above procedure goes against many things we are taught, (such as mixing 5 quarts of clean oil and 1 quart of dirty oil equals 6 quarts of dirty oil) but I am convinced getting the Dextron III out and getting the Dextrin VI in is a major plus against transmission failure do to fluid that has lost its protective qualities.

I have learned that the best way is to hook up the clear tubing to the cooler line and run the truck. as it drains into a bucket, add new oil through the dipstick tube. this will ensure every bit gets exhanged. then after a 100 miles or so you can drop the pan to change the filter and then replace the 5-6 quarts that you lost. I did it the wrong way by dropping the pan first and then i ended up removing the valve body to clean and inpect it and i found a lot of water in the oil and a rusty separator plate too. now i wish i had flushed it first and then dropped the pan. because now i still have that dirty fluid in the rest of the tranny. I wonder if once i put it back together and then fill the fluid up but disconnect the tranny line and run the truck and watch as clean fluid comes out. i wonder if that would work after the fact?