Engine/Transmission (1998.5 - 2002) 4x4 transfer case vent tube location

[TomGolden]

Hi all,



My transfer case is leaking, and I finally found out it is building up internal pressure and spitting out from the small rubber plug on the top of the T-case. I had asked about this in someone else's thread a few weeks ago, and someone responded that my vent tube was plugged and I just needed to clean the end cap off so it could breathe again. At least I believe this is what's happening. I replaced the rear output seal in the T-case about 4 months ago, and it was in fact leaking then, but i9t is not the culprit this time.



Well, I have looked all around the beast, and the only thing I can find coming out of it is what appears to be an electrical wiring harness. I follow it and it runs up into the engine compartment right along side the "T" in the return fuel line right at the rear of the engine block.



When I remove the rubber plug in the T-case, and wipe off the case, I don't see any leaks or drips for a couple weeks, but then it comes back. I am about to leave on a hunting trip to northern Utah, and don't really want to have any problems...



Can anyone lend any hints as to exactly where the darn vent tube really comes out?



Many thanks,

Tom

 

[Rman]

Where you hunting Tom? You going to Elk hunt? Muzzleloader deer starts next week for me.



As for the vent i think there is a plug in the top of the tailshaft housing. Perhaps it's clogged up. If not then your seal may be bad. If you do replace the seal, there is a collar that is notoriously bad as well. Replace them both would probably save you some headache.

 

[Texas Diesel]

I cant be sure but I think the vent tube is on the passenger side of the transercase and goes up the engine side of the fire wall, I'm not sure though.



The rubber plug on the tailshaft housing has been redisigned, they would collapse. The revised plug has a stiffener in the middle to keep it from collapsing, make sure you get the revised one.

 

[TomGolden]

My dad and I are headed for Vernal, over in the north east corner of Utah. Heading out for October 4th opening day. Modern rifle season.



The plug I referred to is on top of the tailshaft housing if I remember right Although there could be something else there as well. Kind of hard to see up there, and I felt around many times with bare hands before I even felt the rubber plug that I am talking about.



I'm not sure I get what you mean by the collar. I did replace the seal on the output side of the drive shaft going to the rear axle. I popped the seal out with a screwdriver, gently tapped the new seal in with a brass mallet, and that was that. When the thing leaks now, I never see any in the area of that same output seal, it is dry as a bone, top and bottom, so that's why I say I do not suspect that seal this time. I could be wrong though. I remember at least one or two other folks telling me they have had to replace that seal many times... Mactruck might have been one of those folks I seem to recall.

 

[TomGolden]

Tejas, thanks for the info on the new plug. I have only removed the plug 3 times, and going by feel, it doesn't seem to have ever been collapsed, but I can't say what it is doing while the truck is moving... I'll see if I can order a new one.



If anyone has a part number they could toss my way...

 

[Rman]

I go elk hunting up there every year almost, around the redcloud loop. Its a pretty good place, i normally get one. My father-in-law got a nice 6 point down on the paunsagaunt last week.



The rear seal fits into a collar, but if yours isn't leaking then there was probably nothing wrong with it. I'll have to check my T case tonight, i'm not exactly sure where it's at i've just read about it.



My transmission leaks and i've been fighting that thing for a while now.



Good luck and maybe i'll come across ya out there hunting.

 

[TomGolden]

My dad has hunter Vernal several times, done Ok, doesn't get one every year, but good enough to keep going back. I can't say exactly where we'll be, as I've never been there, but you can't mistake my truck Stop in if you pass our camp by.

 

[jrobinson2]

Tom

The T case vent on my '99 is on the front top of the case close to the transmission, the hose goes to a green vacuum line that also connects to the center axle disconnect valve on the top of the T case, the green line goes up the firewall and ends with a small 90* fitting with a filter above the lift pump. I think the "wiring harness" you are following is the tubing harness for the CAD that contains the green vent tube line.

Jared

 

[John]

I have an NV241HD in my '98. 5 2500 QC 4x4. I had been going through numerous output shaft seals too. As I have had many New Venture Gear as well as New Process (same company) transfer cases, I had ignored the possibility of looking at a possible "blocked" transfer case breather tube because of previous design shortcomings that produced much the same seal leaking symptoms. After looking through the maze of hoses that paralleled the OE transfer case breather tube, factoring in the internal diameter of said hose ( ), I determined my best course of action was to bypass the OE breather hose entirely. To which; I found a suitable plug for the vent hose, tie-wrapped it to the other nearby hoses, and added a short length of breather hose directly to the transfer case breather fitting, routing the hose over to the driver side frame. From there, I installed a spare, hooded plastic "one-way" breather cap (just like the one used for the front axle), with the end of the hose to the top, inside channel cutout of the frame (for protection). So far it has worked very well.

 

[TomGolden]

John, where did you happen to find this one-way breather cap you used? NAPA or similar parts place? This sounds like a wonderful idea.



Thanks a ton guys!!

 

[y-knot]

I think the other poster was right, what you are calling a wiring harness is really the vacume feed line. If you get under your truck, on the drivers side of the t-case. Get behind the t=case and with a flashlight look up on top of it. It is very tight in there, but cram your face on up in it. You will see a 4-way block sitting on top (transfer case valve connector),

1. green line vent

2. red line CAD disengage

3. lt grey line vacume in

4. black line CAD engage

(CAD central axel disconnect)



The red and black lines go to the front axel, the black line and the green line go back up the passenger side under the hood. Right around the firewall on that side the green line should end, the black one goes accross the firewall to the drivers side where it tee-s in to the main vacume line. I don't know it you are the original owner or not, so if not someone could have messed with it (there must be a reason you are not getting the proper venting), so try and follow the two up. Good luck.

 

[kess]

The vent is just as everyone has indicated-right above the lift pump, against the firewall. I had the same problems with leaking from the rubber plug. I removed the head on the vent tube, blew it out and since (4 months) I have not had one leak.

Later,

Kess

 

[John]

Tom, the reason I previously stated it as being a "one-way" breather cap is because in theory they are supposed to function that way although, in reality, they don't quite perform as well as one would hope. However, I had a new one in storage from a previous GMC 4x I had owned. I would imagine it could be purchased from Dodge parts or for sure from a Chevrolet or GMC dealer. It's just a simple, push-in, white plastic bodied/light green hooded, "one-way" check valve. You should have one at the end of the front axle breather hose (located just beneath the OE air filter base housing assembly on the passenger side fender well).

 

[TomGolden]

Update

Well, I finally found the darn breather line cap. It was in the "wiring harness" just like you all said. The breather cap is just up behind the "T" in the return line, by the IAT and MAP sensors. I was just able to reach it from underneath the truck.



I removed the cap from the line and blew it out with my air compressor. It looked clean as brand new, no oil or other visible gunk like I would have expected. Maybe that tells me it wasn't venting at all... hmmmm. Anyway, I also blew into the line with my mouth, to see if I could detect any blockages in the line, and it blew clear, so I'm hoping it is open all the way back into the transfer case. Will keep a close watch on it and see what it looks like next weekend.



Thanks for all the suggestions everyone.



Tom