Today while replacing my #2 upstream O2 sensor I noticed three semi-rigid plastic tubes resting on top of the cat. The ends on all of them were melted through. The tubes are about 1/8" in diameter and all three of them appear to be running along the passenger side of the transmission and are fastened to something on top of the transmission or in the trans tunnel. I looked around and couldn't find anything that they appeared to go to. The truck is running fine and I am not showing any codes so I assume they are not vacuum lines. Does anybody have any idea what these tubes are and where they should be routed?

Thanks,
Mike

 

Could be a couple of things, there are plastic vent lines for the trans and transfer cases, and there are some vent lines for the evaporative loss system (part of emission control) that run from the engine compartment to the evap canister which is on the frame rail, passenger side, behind the trans (next to the rear driveshaft) if it's one of those you will probably get a fault code after the second drive cycle.

 

That is exactly what they were and you should replace them ASAP so you don't develop a fluid leak from one of them.

 

Those used to attach to the firewall on the right side.
They had a little 180 degree bend to them.
I would get those reattached to the firewall if they are still long enough.
They are vent tubes.
So, the melted end needs to be opened and high up.

 

AH-HA! I love this site! I was under my rig trying to find the "Fix It" button for a sound that was a bit like a mechanical chipmunk chittering away (only under acceleration and inconsistently). I spotted the melted tubes and I *think* I may have found why my CEL keeps kicking on. Now I get to see how to repair/replace them!

Thanks, guys!

 

You need to trace the melted line back to determine which of the 2 possibilities I gave you in my earlier post. If you feel along the tube from the point at the cat where they melted and the line terminates at the top of the trans or transfer you will feel a bolt at the end of the line, then it's a vent line for the trans(or transfer) It's a hollow bolt that goes through a banjo fitting. If, however, you follow the line down the passenger side of the frame rail (above the transfer case) back to a black plastic box with a metal shield around it, then it's a evap line) there are 2 plastic lines for the evap system that run forward. And there are two vent lines from the trans and transfer that run forward. The confusing part is they are both identical in appearance. The vent lines will not cause a CEL to come on, but an evap line certainly will. The vent lines can be repaired with some tubing that slides over it and isn't really important unless you have a habit of driving through deep water. The evap lines, on the other hand, have to withstand both pressure and vacuum in it's operation.

 

I crawled back under the truck today and found the evap lines and they are intact so these must be the vent lines. I was able to feel back on the lines and found one of them terminating at a banjo fitting on top of the transmission. The other two appear to run farther back. I would assume one is for the transfer case but that still leaves one vent tube unaccounted for. I located the front axle breather tube which runs up along the drivers side of the firewall, and I read that the rear axle comes up behind one of the wheel wells. Any idea what the third tube is for and where they should be routed? I looked long and hard on the passenger side of the firewall and I could not find any remanents of broken lines ar even any clips or anything that would give me an idea where these vent tubes were supposed to be.

Regards,
Mike

 

The vent lines will have a "shepherds hook" at end of them (kinda like an old snorkel) and they're supposed to run on top of the trans up to the firewall and the secured at just about the level of the intake manifold. The banjo bolts are sometimes a pain to get at so many mechanics just unclip the vent lines from the firewall and pull the lines down with the trans when doing a rear main seal (and believe me, every Disco has had at least one rear main seal replacement, I've even done them on new ones before they were ever sold) A lot of techs never reattach the vent lines to the firewall because in their mind, the typical owner will never ford any water deeper than 2", Can't think of what that third line would be for. I just did my transfer case last weekend and all I remember is the 2 evap lines and the 2 vent lines, but I wasn't focused on the plastic lines. Does the melted one go anywhere? I would just trace and try to find out where it goes, it might be the end of one of the vent lines doubled back on itself. I just looked at RAVE and the vent line for the trans does indeed double back on itself so the only one that goes to the firewall is the transfer. I must have been thinking about a RR because both of those go to the firewall (I think). If you have RAVE look at page 599, there's a drawing of the trans/transfer that shows the vent lines.

 

I was just looking at that same diagram now it is clear. One of the melted tubes did seem to have a hook on it at one time. The other two ends must have been the loop in the transfer case line where it doubles back on itself. That would give me the three ends which all appear to go to the same place. Now I just need to figure out which are the actual trans and transfer case lines and which is the now severed section that goes to nowhere. I will extend the trans and transfer case up into the engine bay and secure it up high somewhere. Thanks to everyone for the help.

 

Glad I found this.

I've 3 melted tubes about 2 inches from the shepherds hook as described right at the firewall. I suppose I can just cut them a few inches short and carry on. I am wishful that my T-case leak is caused by the pressure and that cutting these open will fix the problem.