Vacuum problem?

[Mowagon]

Hello, I've been lurking here for a while and just registered. This is a great site an I've already learned a great deal.
This is my (current) problem: I hear A loud hissing noise coming from under the gauge cluster area. It goes away when I give it gas or pull up slightly on the hi/lo lever under the driver's seat. When I'm at a stoplight or just coasting is when its the loudest. Can anybody tell me where to start looking?
Thanks for any help, this has been driving me nuts for a while.
Dave

[Bob Barry]

That's the factory-installed pit viper. It will bite your knee if you baby your truck...

;)

Sounds like you've got a leak in the hoses going to your 2wd-4wd selector switch, or the switch itself. Vacuum is highest when cruising, so the hiss goes away when you step on the gas and the vacuum drops.

I would adjust the linkage, both mechanical and vacuum, on the top of your NP229 transfer case, and check the hoses under the dash for leaks. If they are fine and the hiss continues once the linkages are adjusted, then I would listen carefully to whether the problem lies in the switch itself.

It is also possible that the sounds is coming from your heater-control vacuum lines (less likely) or the cruise-control disengagement switch (which I believe is vacuum controlled). The fact that the position of your low-range lever has an effect on the sound leads me to think it is more something with the 4wd switch.

BTW, does it shift into 4wd smoothly and consistently?

[Mowagon]

Thank you for the reply! When I engage 4wd I hear a hiss and it usually takes a while for the indicator light on the dash to light up. It seems like it engages faster if I'm moving. Shifting from park to drive a couple of times seems to help it along too, although that might just be my perception. I've never had it in low range.
I'm still kinda sitting the fence on whether to keep this thing or dump it. The fact that I've already spent thousands just keeping on the road has got me leaning in the keep it direction.
Thanks again.
Dave

[Kimbrough]

Hey Mowagon - first of all welcome to the board!

I had a similar problem when I purchased my '88 GW. The switch inside the cab was "hissing". My problem was twofold: there is a black plastic ball under the hood in the center of the firewall - mine was cracked. A typical problem with these is the hard-plastic line gets broken off the fitting and is hard to see. Check that.
Next, there are 2 vac lines on TOP of the t-case but underneath the trans tunnel (the "hump" on the front floor). I had a crack in one of those lines. IF you suspect that might be a problem - its easiest to get to if you remove the "hump's" cover. Check that last! ;)
Good luck!

[Mowagon]

Thanks for the welcome and the info! I'm going to check this stuff out and see what I'm in for. My luck with this GW has not been that great so I'm expecting the worst case scenario. I found out if I always expect the worst with this Jeep I'm seldom disappointed!
Thanks again,
Dave