So I’m having an issue with my 2001 4 x 4 1500 where the 4x4 light intermittently turns on while in 2wd. It will randomly just flicker and sometimes stay on when I’m driving at highway speeds. It makes a SLIGHT clicking noise while this is happening (sounds like it’s the shift fork trying to engage the axle). I did an inspection of the CAD with 4x4 on engine running and can’t hear any obvious vacuum leaks, but I’m 90% sure that’s the culprit here because I have the infamous blend door malfunction at more than half throttle, and a pretty healthy whistle when driving around 1500 rpm’s. I will be taking a closer look to track down the vacuum leak this afternoon, any tips are greatly appreciated. Additionally, I was thinking of changing to a cable system to prevent further issues. Anybody have opinions on posilocks?

 

The metal lines between the t-case and front axle are notorious for rusting out. See what kind of vacuum signal you are getting at the cad in both 2 and 4 wheel drive... it's likely weak.

 

how did I know you’d be the first reply lol. That seems very likely considering the symptoms. The clicking will magically disappear if I leave the truck in 2nd and let the motor build some good vacuum. I picked up a new actuator just in case, fingers crossed it’s just a line with a leak. I’m thinking about switching it to a cable actuator anyways, vacuum is just overall garbage.

 

Properly setup, the vacuum system works fine. Does it have it's issues? You bet. But so does every other axle disconnect system. And yup. The diaphragms can be problematic. Been there, done that.

 

Okay so looks like only one of the vaccum actuator hoses is working, the one that takes it out of 4x4 is completely dead. No leaks on the line that I can see, should my next step be to take the lines going into the transfer case? I’m thinking it might be a stuck switc, I saw somewhere on this form that you need like a 28 socket?

(edit) so there was a small leak near the 4x4 actuator which I fixed with tape temporarily, but there must be a bigger leak somewhere because I’m getting very weak vaccuum from the 2wd side of the system all over.

 

okay well after messing with this thing for 3 hours I believe I found the culprit. It was actually the first and only leak I found. After taping it the truck definitely shifts in and out of 4x4 and stays in/out. Firstly, I’d like to say I kindly disagree with vacuum being a good system,I’ve had 2 rangers and now this dodge with vacuum problems, maybe it’s just my luck! Either way, I think I’m going to throw a cable CAD kit in her, it just seems like a better option given the lines I was foolin with today are definitely showing their age, and I really don’t feel like buying all the new lines and what not. Maybe I’ll just buy the kit and have it on hand for when the vacuum system take a poo again. What do you think ?

 

This is my second second gen. I had to replace the diaphragm on both of them at one point, fix a few rusted lines, etc. But, once I had the system in good shape, they worked reliably, I DID have one odd problem though. Moisture got into the lines, and froze..... No 4x4. Had to park the truck in the garage, point my torpedo heater under the truck, get things thawed out, blow out the lines. No more issues. My current truck, that diaphragm went bad, but, that is the only problem I have had with this one. System still works perfectly, every time. (I have had this one since 2017...)

My major issue with the cable system is the cable itself. Gotta route that thing somewhere..... and if you off-road in heavy brush, it is a potential candidate for getting caught, and ripped out. Proper routing can reduce that possibility..... The one SERIOUS advantage of the cable system though? 2wd Low. Awesome for moving trailers and such around.

 

I've had my 2nd gen from -06. When I bought it, I had no 4wd. Issue was at the CAD, shaft that moves the fork was stuck to the housing. Untill I found that, I went through all the components and zip tied rubber couplings on the vacuum lines.
After that, truck was my daily driver to the end of 2019, drove it some 200 kmiles, never had issues with the CAD. That 200 kmiles included winter driving, offroading and everything you could with it. I'd say vacuum CAD is a solid system.

 

Then we have the GM system from the 90's. On the full size trucks, it was a thermal actuator. Put the truck in 4x4, and it passed a current thru the actuator, warmed it up, and it would lock in the front axle. (similar to our CAD) Only problem was..... If you drove in deep snow, it would pack around the actuator, and cool it enough that the front axle would disengage. So, 4x4 would quit working when you needed it the most.

 

that sounds like a real stinker! I guess I’d be reasonably happy with the vacuum if I was competent enough to maintain it hahah. Truth be told, I’m lazy and really just like my stuff to work forever without lookin at it. I’m also pretty hard on it off-road, pretty much every weekend it’s getting abused. I’m gonna throw the Posi lock in her and keep the vacuum system around for a while in case I change my mind. Otherwise, I still have to fix my wacky vent issue, does anyone have a link to the tsb by dodge for that?