Leak behind dash? Dripping off the front axle shift lever? Read here.

[TexAndy]

Ok, just wanted to make a post about my experience with this problem.

The symptoms: Air shift valve would spray oil out the little vent holes on the side (on side more than the other) when flipping it to "out." And it would slowly ooze gear oil after shut down.

First I tried taking the transfer case vent out and cleaning/lubing it. That helped some, but did not completely fix the problem.

Then I pulled the air line running from the lever to the Transfer case where it connects to the transfer case to blow any built up gear oil line out. That did not solve the problem.

So I started looking at the valve itself. I noticed that on my nicer-looking parts truck take-off, the valve had alot less slop in the lever. In my old one, there was quite a bit of sideplay.

AND, I noticed that when I turned the engine off, I could hear air escaping out of the front axle engagement switch. Not just the initial pressure relief *pssh* but a constant hiss as long as the system had air pressure. I'm pretty sure that's NOT supposed to happen.

So here's my theory of what was wrong. That old air shift lever had a bad seal in the "out" position, so that instead of sealing, it was actually leaking air, which in turn created a slight vacuum in the air line running to the transfer case and sucking gear oil up the line.

I went ahead and swapped the assembly out for my parts truck's air shift lever, ran the engine for a few minutes and cycled the switch a half dozen times. I can already tell a difference. It doesn't leak air in the out position.

On a side note, those little air shift lever brackets are REALLY HARD to pull and replace at 3 AM with no one to hold a light for you.

Anyways, hope this helps someone else with this problem. Just thought I'd compile all this info in one post to make it easy to find. I used plenty of common words so a search should turn this post up without trouble.

 

[airmech3839]

I have the same issue. But I also have oil leaking out the seals. I have lossened the vent since it wont stay un-stuck. I have to service the case frequently to keep oil full. I have a loose speedo hook up. I have oil all over the valve on the case and oil coming out in cab. You just changed the one in the cab, right? I got a new shaft seal for my rear seal since it was initially my first sign of leakage. What does it take to change the seals out and what about the valve mounted on the case itself?

 

[TexAndy]

That I do not know. I just swapped the unit that bolts to the dash. That was the valve that was causing my issue.

 

[Zadvark]

A quick resurrection of the thread. Am I to understand that a replacement of the in-dash control valve fixed this issue? I don't have a discernible leak per se but I always got a little shot of out out the from slot when I disengaged the front axle.



I didn't notice it at first but I ruined my favorite pair of work boots after a 15 minute ride

 

[DieselBob]

I always got a little shot of out out the from slot when I disengaged the front axle.

That is normal in the operation of the valve. It is releasing the pressure from the cylinder on the transfer case. You should not have air escaping at any other time.

As far as the oil it most likely is residue from the moisture and oil vapor that has accumulated in the air system the last 40+ years. There is a slight chance that some oil might back feed from the cylinder on the transfer case back up to the valve but that would require the seals on the engagement piston to be bad and the vent for the transfer case to be stuck closed allowing pressure to build in the transfer case and force gear oil past the piston and back up to the valve.

 

[cmpman]

The Canadian solution.

I had over 20 years maintaining the Cdn M35s, so here is what I know about the subject.

The Canadian Forces use the M35Cdn which has the air-shift on the dash for front axle engagement. The Canadian models had the problem with the oil coming out the shift switch as well. It all fell back to the breather valve on top of the transfer case. Initially it was blamed on the gaskets on the transfer case decomposing and blocking the breather valve, but eventually the Canadian trucks were supposed to be modified by removing the breather valve from on top of the transfer case and installing a rubber hose that came from the top of the transfer case and looped around the front of the case with a new breather valve installed in that location. The hose was held in place with a couple of clamp loops. The reasoning for all this was that the operators could not service the breather valve in it's original location, but with it visible and accessible they could give the valve a little spin to free them up whenever they were under the vehicle in that area, or when performing a major service.

I suspect the original poster fixed the problem by cleaning his valve, but it would take a bit of time to clear the oil from the line and valve. By changing the valve (which may have become gummed up from the oil passing through it causing the vale seats inside to seep) he reduced the amount of residual oil in that area.

 

[99nouns]

Been there done that... And I don't want to remember, my breather valve was intentionally plugged with rubber seals, I know it is like a conspiracy theory but why would someone do that?

 

[rustystud]

Been there done that... And I don't want to remember, my breather valve was intentionally plugged with rubber seals, I know it is like a conspiracy theory but why would someone do that?

A lot of people are uninformed about the purpose of a functioning breather. They see a potential problem area for water to get into their gear unit. I've seen this many times with customers vehicles.