Ok guys I honestly hate to start another thread but I have a serious problem. It is the dead of winter and my 4x4 won’t work! The engagement stick moves into place but no dash light or 4 wheel drive! I need to get this fixed ASAP! I used it last week so it worked fine then. Help?

CAD Vacuum is disconnected or the vacuum motor is damaged.

5 minutes ago, Mopar1973Man said:

CAD Vacuum is disconnected or the vacuum motor is damaged.

Where is the connections? I’ll check those. 

Here you go a full article for this problem.

 

 

 

Edited December 29, 20177 yr by Mopar1973Man

There are plastic vacuum lines running by the cowl. Start tracing them. There is a rubber 90 on the driver's side cowl that goes down to the vacuum pump that is known to dry rot.

13 minutes ago, CTcummins24V said:

There are plastic vacuum lines running by the cowl. Start tracing them. There is a rubber 90 on the driver's side cowl that goes down to the vacuum pump that is known to dry rot.

I’ll do that. Seems weird it would all the sudden conk like that. I did notice that sometimes when I put it in the light wouldn’t come on until I released the clutch and started forward.... maybe that was a sign that it was goin out?

you might have water in the lines that froze causing the actuator to not get vacuum.

14 minutes ago, Me78569 said:

you might have water in the lines that froze causing the actuator to not get vacuum.

What about taking a air nozzle and blowing into them?

doubt it will work, you will just blow apart the junctions.  It's a vacuum system not a pressure system

If you have been doing in work on the top  and drivers side of the motor it is easy to knock the main line out of the 90 on the cowl. Just had this happen while putting a new starter in this past week. Happens to me a lot while working in this area.

easy way to know if you have a vaccuum leak is if the vents switch or not.  If you have a vaccuum leak it will be on defrost no matter what

27 minutes ago, Me78569 said:

easy way to know if you have a vaccuum leak is if the vents switch or not.  If you have a vaccuum leak it will be on defrost no matter what

I had it on feet and face this morning and I think it was working fine. I’ll check after work.

31 minutes ago, dripley said:

If you have been doing in work on the top  and drivers side of the motor it is easy to knock the main line out of the 90 on the cowl. Just had this happen while putting a new starter in this past week. Happens to me a lot while working in this area.

I was working in that location last night. I’ll have a look after work.

A hand operated vacuum test pump is a good investment, is not that expensive, and will allow you to accurately diagnose vacuum related problems. 

 

For example, the CAD unit can easily be tested.  Place the transmission into a gear and select 4-high or 4-low with the transfer case.  Jack up the right front wheel and disconnect the vacuum lines at the CAD unit on the axle.  Connect the vacuum pump to one port of the CAD unit; leave the other port vented to atmosphere.   Operate the vacuum pump and hand rotate the right wheel to ensure engagement or release of the CAD.  Swap connections and test again.  Assuming that vacuum held on each test, one test should allow the wheel to rotate freely, the other test should lock the wheel in place which means that the CAD is mechanically doing its job.  Using the vacuum pump you can continue with testing of all vacuum lines until you find the source of the problem.

 

If both tests pass and the 4WD light does not come on, then you have a bulb failure, an electrical wiring problem, or a CAD switch contact failure.

 

If the right wheel spins freely during both tests, then you have a CAD failure.

 

Vacuum leaks on these trucks are commonly overlooked until something fails.  The vacuum pump is very powerful and vacuum leaks can go undetected until they become large.  Remember, all air from these leaks pass through the vacuum pump, into the engine crankcase, and then out the breather vent.  You do not need this additional air flow out the breather vent!  This issue alone is reason to invest in a hand operated vacuum test pump.

 

- John

Edited December 29, 20177 yr by Tractorman
content

Here is my thread, some good info in there also.

 

Edited December 29, 20177 yr by Dieselfuture

Just now, Dieselfuture said:

Here is my thread, some good info in there also.

No link here. 

https://mopar1973man.com/topic/12424-front-axle-cad-vacuum-actuator-to-manual-posi-lock/

 

Just for the helpful hand... I post a standard link. @Dieselfuture post does have a link but not what you expect. That whole insert box is the link.

3 hours ago, Marcus2000monster said:

I had it on feet and face this morning and I think it was working fine. I’ll check after work

If it was blowing on your face and feet you do have vacuum to part of the system. If you loose it completely it will blow out of the defrost only as was mentioned earlier. Mine will blow a little out of the floor also. Mine has always done that with or without the vacuum connected.

 When you say face is that from the defrost or the dash vents. I know defrost blows in my face.

Edited December 29, 20177 yr by dripley

58 minutes ago, dripley said:

If it was blowing on your face and feet you do have vacuum to part of the system. If you loose it completely it will blow out of the defrost only as was mentioned earlier. Mine will blow a little out of the floor also. Mine has always done that with or without the vacuum connected.

 When you say face is that from the defrost or the dash vents. I know defrost blows in my face.

Dash vents

10 hours ago, dripley said:

If you have been doing in work on the top  and drivers side of the motor it is easy to knock the main line out of the 90 on the cowl. Just had this happen while putting a new starter in this past week. Happens to me a lot while working in this area.

I’m not seeing where your talking about. Can you give a specific location? Thanks!

19 minutes ago, Marcus2000monster said:

I’m not seeing where your talking about. Can you give a specific location? Thanks!

Found them! So far I’m not seeing any disconnected lines but we’re working on it!

If you look at the vacuum pump and just follow the 1/4" line it will lead you right to it. It is a little over half way from the drivers side to the engine just below the wiring bundles.

But since you have air blowing out of the dash vents, it is not likely disconnected as someone mentioned earlier it will default to the defrost if that line is disconnected.

Have you checked by cad if you got vacuum, and you can put a hose on actuator and suck vacuum on each fitting and it will engage and disengage. If all checks out there, then there is something by the transfer case that I never messed with myself but I know it's there. I wanted to eliminate as much as I could with all that vacuum stuff that's why I went with a cable instead, plus having a 2low is nice for backing up hill with a trailer, which can be done other ways. I just wanted to try posilock, and my actuator was on the way out so I was almost half way on the cost just replacing it.