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Waterproofing Your Transmission

The following writeup was performed on a 2001 TJ & and on a 2002 TJ. Both have the 5-speed NV3550 transmission. This may or may not work with any other transmission (I have no idea), use good research & judgment before trying this on a transmission other than the NV3550.

Once upon a time, while crawling underneath my Jeep, I was snooping around the transmission and transfer case. On top of the transfer case (NP231J) I found a hose that ran up to the top of the bellhousing of the transmission (NV3550). This hose led to a breather vent on the transfer case. I began wondering if the transmission had a vent also. After feeling around for a hose, I couldn't find one.

tranny breather ventThen, it happened. I found what felt like a breather vent dead center on top of the tranny. In the picture at left, pretend you are laying on the passenger side with your head where the front tire is; your feet are to the rear of the Jeep. You are looking up, right and to the rear. The vent is circled in red, the tranny bellhousing is to the right of it. Sorry for the strange photo, but there really isn't a better way to get this picture. (Click photo to enlarge)

The lowest breather valve on the Jeep will dictate how deep of a river/mudhole you can traverse. It kinda of relates to the "weakest link" theory. Both differentials have vent tubes that vent at about the height of the door handles, so why not make the transfer case and tranny match right?

This project should take 1-4 hours depending on how difficult the breather vent is to remove for you, and how many hardware store trips you have to make. Follow along in the guidelines below and you should be just fine.

Parts List

Tool/Supply List

The Procedure

Step 1

First, open the hood, get out the shop light, and gather your tools from the list above. Put on your safety glasses. Crawl under the Jeep with your visegrips, locate and remove the transfer case vent hose. Now with the t-case hose out of the way, take the visegrips and remove the transmission breather vent. It's NOT threaded in there, all you have to do is twist and pry (It's not as easy as it sounds). Here's what the factory vent looks like:

Step 1 remove the t-case hose and tranny breather vent

Step 2

If the flimsy crimped on cap hasn't already come off, take your visegrips and go ahead and remove the cap. After the cap is off, use your metal file or bench-grinder to remove the ridge around the top of the vent that the cap was previously crimped to. Just grind it smooth so that it is the same diameter as the rest of the vent. This will ensure proper seal when we next solder the copper elbow to the vent.

Step 2 Remove the vent cap.   Step 2 Grind off the ridge that held on the cap.

Now that you have the vent out, and step 2 is finished it's a good idea to head to the hardware store (bringing the vent with you) to make sure that you get the right parts/sizes. There could be slight inconsistencies in part sizes between years/models.

Step 3

Now that you have all of the parts, get the vent, the 90 copper elbow, and your solder/MAPP torch. First blow out any dirt/shavings from the vent and elbow-we don't want any crud getting in the tranny. Stick the ground end of the vent into one end of the copper elbow. Grab ahold of the elbow with visegrips and light the torch. Solder/sweat the vent to the elbow. After it has cooled off, stress test the soldering job for strength.

Take and test fit the barbed poly connector into the other end of copper elbow (which may require some trimming/whittling for correct fit). After test fitting, smear some RTV on the poly barb and permanently insert it in the copper elbow.The completed vent assembly looks like this:

Step 3 completed vent assembly

Step 4 - Reassembly

Get the new vent assembly, the 3-way "T" connector, mini-hose clamps, and some RTV. You'll need to trim the OEM transfer case vent hose so that it ends about six inches from the tranny vent hole. Slide a hose clamp over this hose, RTV one of the 3-way outlets. Then insert the RTV'd 3-way tip into the OEM t-case hose and snug down the hose clamp.

Step 4 completed vent assembly ready for installationTake the new hose you bought and cut approx. 1' off. RTV another tip of the 3 way, and insert it into this new length of hose. Slip a hose clamp over the open end of the hose and slide it down and tighten it to the end you just hooked up. This is the section that will link the t-case and tranny vents together. Slip another hose clamp on there, RTV the poly barb end of the modified tranny vent and connect the tranny vent to the hose (you may need to trim this hose first to make sure the extra length doesn't cause kinks or get snagged on anything). The modified tranny vent should still NOT be installed in the tranny. Now RTV the last remaining port on the "T" connector. Put your 5' piece of hose you bought on this port. Slide a hose clamp down the hose and tighten it up. Now run the hose up towards the tranny bellhousing/engine compartment; this will help keep it out of your way.

Very carefully RTV the tranny vent and glide it into the original tranny vent hole. You may need to use a screwdriver or a similar tool to pry against the body; this will ensure the vent is secured/sealed into the tranny.

Step 5

Step 5 Routing the vent hoseThe final step is to get under the hood and route that hose from the "T" connector up into the engine compartment and secure it out of the way. In this photo, you can see that I zip-tied it at the top edge of the hood to an electrical harness. There are 2 things to note here:

1. When routing the hose, make sure it is routed away from moving parts, and hot parts. We don't want to shred or melt the hose.
2. DO NOT reuse the breather check valve like I did in the picture (green thing in this picture). Due to the length of the hose, that valve restricts air flow too much and could potentially cause transmission or transfer case damage. I just removed it and left the plain hose.

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Page created on 5/28/2003
Last updated on 4/20/2004