hi everyone..

one of my buddies has a 98.5 24v and something in his 4 wheel drive is going out.

One of the hard [vacuum] lines going to the central axle disconnect under the truck was rusted/blocked, so I bent up a new hard line, flared it, and installed it. The truck now goes into 4wd. We went for a test drive and it worked great for about 10 minutes, then the 4wd light started flickering on and off, and you could feel the front axle engaging and disengaging.

I got back under the truck and checked the two vacuum lines where they connect to the CAD actuator, both lines pulled 25 in/hg when shifted between 2wd and 4wd. So the vacuum pump and lines are all fine. What is tehre to go wrong in the actuator itself? Its almost like the engagment fork is only partially engaging? Are there seals in it that could leak enough vacuum to only allow it to partially engage? Is it a big PITA to pull the CAD module out of the front axle? Ive never played with a vacuum one, only electric CAD's...

btw the truck has 260-something thousand miles on it, do the CAD's wear out due to mileage?

thanks
ben

 

if you talkin about the vac. lock hubs yea they can wear out. i did a set on a ferd 350, wants bad to do at all. but i have a feelin your talking about somethin' else

 

There is a rubber diaphragm inside the actuator "can" that does wear out over time. A few solutions; a new unit($$$), a junkyard actuator, or a Posi-Lock(@$200). You could also do a home-built Posi-Lock, do a Google search, you should find a few articles on it. HTH

 

alright thanks for the advice, Ill pull it apart next weekend or something and see what it looks like inside. If its broken we'll probably rig up some sort of posi-lock setup..

thanks
ben

 

I just bought a new CAD ($100) and vacuum switch ($22) to try and solve my problem. Pretty cheap to get new parts....

http://www.1aauto.com/1A/4WDrive/Dodge/PickupFullSize

 

Same problem, except neither line to the CAD will pull a vacuum. Just to clarify, I disconnected one of the lines and put the vac pressure gage on there, started her up and threw her in 4wd, but left it in neutral so the truck didn't drive off while i checked the reading. No vac on either red or black.

Think vac pump is bad? I also can't get cruise control to come on, the light comes on but it wont engage. Also I don't get anything other than defrost when I mess with the fan settings inside. (no air will blow out of any vents aside from up the dash onto the windshield)

Don't mean to steal thread, just on the topic. Thanks.