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Old 06-24-2019, 03:58 PM   #1
Join Date: Feb 2017
Location: Milwaukee, WI / Denver, CO
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Default Replacing Rusty Transmission Cooling / Cooler Lines

While the problem of severely rusted transmission cooler lines has been commonly referenced in T1N Talk there doesn't seem to be much in the way of documenting how to replace the lines. Perhaps it's because on the surface it seems like an easy fix--remove old line, install new line--but when I looked into actually doing that it seemed a little more complicated. So I wanted to start this Write Up so I can share what worked for my 2004 2500 and hopefully you'll share what worked for you.

The transmission cooling supply line run from the transmission to the radiator, where the fluid is cooled, and back to the transmission via the return line. There are 3 parts to each of the lines:

Supply: Starting on the drivers side of the transmission a small diameter metal pipe is connected to the transmission with a banjo bolt. The line runs along the passenger side of the oil pan. Once passed the oil pan towards the front of the van the pipe ends and is attached to a hose of the same interior diameter. The connection is a permanent crimp connection, and in my estimation it's not possible to disconnect the two and then reattach them without special tools. The other end of the hose has a threaded nut(which is attached to the hose using the same permanent crimp connection as the other end) that connects to another metal pipe section, and that pipe connects via a threaded nut to the passenger side bottom of the radiator.

Return: The fluid exits the radiator at the passenger side top and follows the same route as the supply line--pipe from radiator, hose, pipe running alongside the passengers side of the oil pan and back to the transmission where it is connected via another banjo bolt.

The sections of line that seem to corrode most frequently are the 2 pipes that connect directly to the radiator. They corrode at the fittings to the radiator, making it nearly impossible to remove them from the radiator without ruining the radiator. I had significant corrosion at these areas, so I figured it was best to get ahead of it and just replace the radiator while I was at it. If you replace these lines due to corrosion, you will more likely than not need to also replace your radiator, so be prepared.

Vic did come up with a solution that worked for him, saving him the need to replace the radiator. You can see that here can see here:


It's worth mentioning at this juncture that the two places that there are threaded connections(pipe to radiator and the other end of the same pipe where it connects to the hose) the nut does not create the connection/seal--the seal is created by the two ends of the fittings mating with one another--the threads simply keep them held in place. This is important for the DIYer to note because while it would be extremely easy to skip the radiator pipe section which is doomed to rust and simply run a transmission hose and hardware store brass fittings at either end--that's not going to work(I was hoping it would, to just do away with the entire pipe section altogether). You could however cut out the middle section of an old(or new) pipe and run hose between the two ends similar to what Vic demonstrates above. Just be sure pay attention to his advice on connecting a pressurized hose to a non barbed pipe end.

As far as I can tell from the parts manual and from information shared by member billintomahawk--MB originally had a different part number for all 6(3 supply, 3 return) sections of these cooling lines. At some point, they decided to combine the transmission end banjo bolt pipe and the rubber hose section. So if you want to replace EVERYTHING, you need to know that, because you probably aren't going to find all the original parts when searching for their numbers. Here's more info from Bill's helpful post regarding this:

[QUOTE=billintomahawk;673728]Transmission lines.
Mine are rotten so I went after them.
I keep hoping this is a nightmare and I will wake up, so far that hasn't happened.
First I find out the trans cooler fitting on the 'radiator' is stripped. So I need a new radiator.

Ok, I find a radiator and get that ordered, next order replacement lines. No problem....
Wrong, problem. The part numbers are a mess because MB eliminated the 3 piece line and now supplies a single line on either side of the engine...I hope.

Seeing will be believing. Here are the updated lines.
I'll be updating the results.

Obviously the rubber hose sections won't corrode although the crimp fittings at either end can/do. Mine were badly corroded where the radiator pipes met the hoses--not so much where the hoses connect to the longer transmission side pipe. It would have been an easy fix if I could have just removed the nuts connecting the hose to the rusty radiator pipe sections, but there was no way that was going to work without damaging the nut which I need to reuse.

For me, the pipes that connect on the transmission end via banjo bolt have some kind of black coating on them and were not rusting at all--not sure if that's standard or not but for me those sections didn't really need to be replaced and I didn't want to replace them if I could avoid it. As mentioned above they run alongside the engine oil pan. They are actually held in place by guides that are bolted to the lip of the oil pan and thread into the engine block--therefore, in order to place these sections of the new lines properly you would need to loosen 6 of the oil pan bolts. I don't think I need to elaborate any further why that would be less than ideal. You could get away with cutting these sections of the old line out and using zip ties to secure the new ones(or even zip tying the new to the old leaving the old disconnected in place), but I figured if I could figure out a way to keep these sections of the line in operation I would. Bill replaced his entire lines, but after messaging him about it, it seemed like his 2002/3 did not use the same oil pan guides as my 2004. He did report that he was able to remove and reuse the banjo bolts connecting the lines to the transmission, which may be helpful for some as finding replacement for the bolts and seals was difficult and when I did find them they were around $50 total for two bolts and washers.

I ordered a new radiator and all of the necessary pipes/hoses to replace the entire line--I wanted to be prepared for the worst case scenario, and at the time of ordering I didn't have another plan in which I could leave the transmission side pipes in place. Here are the part numbers for the cooling line sections:

Return--05119993AA(radiator pipe), 05117856AA(combined hose/transmission side pipe)
Supply--05119991AA(radiator pipe), 05117857AA(combined hose/transmission side pipe)

My "aha moment" came after mulling over Vic's linked post above and after getting under the van and just staring for a while. I guessed that if I could find a barbed fitting/splicer that matched the interior diameter of the hose section of the line, I could just splice the two sides together in the middle of the hose. This would allow me to replace the corroded radiator pipes, the corroded connection from that pipe to the hose, but let me leave in place the transmission side pipes which were not corroded.

I measured the ID of the new pipes and ordered these:



I used these line clamps from Harbor Freight:


I clamped off the lines on the hose sections where I thought it would be easiest to make the splice. Access is easy as the hoses are right at the bottom of the radiator. You don't need to make perfect length measurements as the hoses will give you a bit of wiggle room as far as tolerances are concerned. With the line clamped off I used a PVC pipe cutter I have to cut the hoses on the radiator side of the clamps. If I was smart I would have used the other 2 clamps and cut in the middle of the clamps, but I didn't think of that . Obviously you are going to lose a bit of transmission fluid here, but it isn't much. If you don't clamp each hose in 2 places some of the fluid will drain when you make the cut, so have an oil pan handy. I'd just replaced my fluid a day before so I was already in the process of monitoring and topping off the level.

With lines cut I removed the radiator and installed the new one. I connected the new radiator side pipes. I held up the old sections of hose that were removed up to the new sections of hoses I had(05117856AA and 05117857AA), and I cut the new hoses to approximate length, from the nut end that connects to the radiator pipe to where I wanted to splice the hoses together. Now, remember that MB changed the hose and transmission pipe sections from 2 separate parts to 1 combined part? Well, unfortunately in going about the fix in the way I was, I had to accept that I was only using a connector and few inches of hose from two parts that cost about $75 each. SNIP SNIP.

I grabbed my barbed fittings and hose clamps and spliced the new section of hose to the old and connected the hose to the radiator side pipes. Don't forget to remove the clamps. Once the rest of the radiator work was done and coolant added it started right up. No leaks after a couple of drives including a few "drive it like you stole it" highway miles. Don't forget to keep an eye on your transmission fluid as you lost a bit in the process. Top off as necessary.

One tip that will save you quite a bit of money if this method works for you--this part number: 05127830AB. It's number 13 in the 2004 parts manual, page 74. It is the "hose section" of the now sold together hose/transmission side pipe. I am only 99% sure that this will work, but instead of spending $75/each on the new lines like I did, only to cut off a few inches on each end--I would order these for $20/each if I could do it all over again. I considered sending my parts backs and ordering these, but in the end with return shipping/restocking fees, I wasn't really going to come out that far ahead and I was already in the middle of the job when I figured this out. Don't be like me.


Hope this helps someone down the road.

Good luck.
2004 & 2006 2500s
SHC 140

Last edited by RJV; 06-24-2019 at 04:53 PM.
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Old 06-24-2019, 04:01 PM   #2
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Default Re: Replacing Rusty Tranmission Cooling / Cooler Lines

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2004 & 2006 2500s
SHC 140
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Old 06-24-2019, 10:12 PM   #3
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Default Re: Replacing Rusty Transmission Cooling / Cooler Lines

Awesome write up. I am adding an external transmission cooler on my 2005 this weekend and this info will be very helpful.
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