Join Date: Mar 2012
Location: Pepperell, Massachusetts
Replacing Transmission Cooling Lines
First and foremost, allow me to preface this DIY write-up with some invaluable advice. Sometimes you're going to take apart more of the truck to do the job than you originally thought to make it easier. This is definitely one of those occasions.
This write-up will cover the basics of removing and installing 2 out of 3 transmission cooling lines. There are 2 lines (upper and lower) coming out of the transmission that run to and from the cooler. The third line (aux) is an accessory line that runs from the transmission cooler to the radiator thus completing the connection of all 3 lines.
Phase 1: Disassembling Your Truck
You're going to want to remove the following components from the truck:
Upper Fan Shroud
Plastic Skid Plate/Splash Guard (Under Radiator)
Metal Skid Plate (Below front differential and oil pan)
Frame Crossmember below the rear of oil pan
Passenger Side Wheel Well Liner
CAC Tube (Blue hose coming from turbo pipe)
Exhaust clamp under the fuel filter
Trust me, you will want to take all of these apart. Especially the bumper and skid plates. Anyone that tells you it's easy to get the lines in with those on is just trying to puff up their own ego. It's worth the extra 10 bolts or so to not damage your new lines trying to snake them around the engine block and front end.
Phase 2: Removing Old Lines
*NOTE* Make notice of the cooler lines' proper fittings on the transmission as well as the way they are routed. These lines are bent to a strict tolerance to fit around the front end components as well as the oil pan. It will be easier to install if you can remember how they were run before.
Disengage the plastic clips from the quick connect fitting. Pull the caps back along the pipe.
Hold one leg of the retaining clip and using a pick, gently pull the other end of the clip from the quick connect fitting.
Rotate the retaining clip out of the quick connect fitting
Now pull to separate the line from the fitting.
It's also a good idea to re-install the retaining clips now so they definitely won't get lost.
At this point, if you have not disconnected the exhaust up by the engine block, you will see why this step is necessary. The "To Cooler" line from the transmission will be right up against the exhaust making it impossible to remove.
After all four ends of the (2) lines are disconnected remove them.
The lower line, which runs from the transmission to the cooler directly behind the grill, should be pulled through the front.
The upper line, runs from transmission to lower rear side of radiator, should be pulled through the back for removal.
Phase 3: Installing New Lines
Now that you have the old lines out, and assuming you removed the bumper and skid plates, the new lines should go in fairly easily. Once again, I implore you to trust me. I fought for a couple of hours trying to get my new lines in with the skid plates on. Once I removed them it only took 5 minutes to get both lines in.
Personally, I found it easier to install the lower line (labeled "From Cooler" on the transmission) first considering it is longer and has more sharp turns.
Now the upper line (labeled "To Cooler" on transmission) will be fed up from the back of the truck.
After you have the lines run, you are ready to install them into the quick connect fittings.
Install the retaining clip into the quick connect fitting if you have not done so already.
Install using your thumb and forefinger. Insert the retaining clip into one of the three recesses. Ensure that the retaining clip is engaged in all 3 slots.
With one end of the retaining clip engaged in the quick connect fitting slot, use your thumb in order to rotate the retaining clip around the connector fitting, until the retaining clip snaps into place.
Ensure that the 3 retaining clip ears are seen from inside the fitting and that the retaining clip moves freely in the fitting slots.
Install the cooler line straight into the quick connect fitting. Insert the coller line end into the quick connect fitting until a click is either heard or felt.
Pull back sharply on the cooler line in order to ensure that the cooler line is installed in the quick connect fitting.
Snap the plastic cap onto the quick connect fitting and ensure that no gap is present between the cap and the fitting.
Ensure that the yellow identification band on the tube is hidden within the quick connect fitting. A hidden yellow identification band indicates the join is properly seated.
*NOTE* These quick connect fittings can be troublesome to connect to the lines. A lack of leverage compiled with a tight space make it very necessary to guide the fittings in as straight as possible before you go pushing and pulling on the line.
The two quick connect fittings at the transmission can be taken off the transmission and installed on the lines first. It makes it a little easier giving you the leverage needed to get the line right.
Phase 4 (optional): Cleaning
I don't know about you, but I know I had to change my lines when one of them had a hole rubbed in it over time and sprayed ATF all over under the hood. Now that you have everything apart (i.e. skid plates), wouldn't it be nice to clean it up?
Hit everything that's covered in grime with some simple green, engine degreaser, or some water and liquid dish soap. Let it sit and do it's thing for about 10 minutes before hitting it with a hose or rags.
In my situation, having to replace the power steering pump twice in a year and the transmission cooler lines going, my skid plate and front differential were disgusting. If you have a pressure washer, now's the time to get it.
Phase 5: Reassemble the Truck
Double check all your work! I recommend that you top off your transmission fluid, start up the truck and check for leaks before completely putting the truck back together. It would be unfortunate to find you missed something and have to take it all back apart.
Once your truck is back together take it for a spin and bask in the pleasure that comes along with being a Duramax owner.
I hope this helps anyone who is going to tackle this project. Tomorrow I will try to get some pictures up to aid you in your installations.
Last edited by Skydive; 12-05-2012 at 11:32 PM.