1999 dodge diesel 4x4 2500. last year replaced the accuator on the front axle. Thought everything was good. Light comes on but front axle doesnt lock in. Came in once then went out. light always comes on.that's what i dont understand,thats where the indicator senors is on the accuator. should be locked in. so trouble shooting ideas is what i need.
1)was going to pull lines off accuator and see how much vacuum i have.
2) look at switch that is some where on transfer case that switch vacuum .
3) Take off accuator and see if its free.
4) Ask for help on here and get some better ideas LOL !
i wasnt laughing earlier . getting calls to plow driveways but dead in the water.(SNOW)
thanks for any help

 

You pretty well covered the way to troubleshoot it. If you have vacuum at the actuator next step is to see if it works.

 

So could it be the switch on the transfer case if it comes off and on?? where is the switch?

 

A stupid easy test I check first is pulling the rubber boot off the actuator at axle, place a finger the vac lines while running in 2 then 4wd, make sure the vac. switch on the top of the t-case is good and that you have any vacuum to begin with. I forget which line is supposed to have vac. on 2wheel vs 4 but it should switch. My light flickers on frequently in 2wd, but everything seems to work well otherwise so I don't trust the light on the dash!

If only vac on one line, switch is probably bad. Swap the lines feeding the axle actuator to get 4wd full time (or at least engage the axle). I've also heard the collar that locks the 2 axleshafts will "roll" into 4wd with no vacuum at all, maybe try backing up while engaging 4w. Good luck.

 

vac switch for 4500 is on the top drivers side rear ward of the "pan"

 

If you do some research on here you will find the vacuum actuated CAD is very problematic. Those capillary tubes for the vacuum are tiny and fragile. When I bought my truck the vacuum CAD was broken. Based on recommendations from folks on here I ditched the stock CAD and bought a Posi-Lok manual CAD activator. Now, when I want 4WD, I pull a **** on the dash to lock the CAD, select 4WD on the transfer case and away I go. Super reliable and no question about whether you are in 4WD or not.
I think I paid about $200 and the installation took a couple of hours. I was super cautious during my install and prolly could have done it in about half the time. If you jack up the front axle on the passenger side, you won't even lose almost any diff/ axle fluid.

Let me know if you want more information.

 

IF the light comes on in the dash, the fork "rod" must be pulled over into that sensor for the light to come on. Thus, you have vacuum and that part of the system is working correctly.
IF not in 4wd? Then the fork is broken or a c-clip on the fork pin is broken. OR, something in that same area.
Sounds like the fork pin is moving, but, the fork is not.
Go back to the last thing you did (replaced the actuator), and make sure the fork is installed correctly.

 

mine did this and I replaced the switch only to find that the wires were broke leading from the switch up towards the frame

 

In this instance, the truck would actually be in 4wd and work, but, the indicator light would not work.

 

Big vacuum leak could prevent engagement as well, but you would probably be having defroster/heater issues as well.

I used the 2low kit from Genos to convert my CAD to manual engagement which has BIG advantages over stock. Like engaging your hubs from inside the cab. Leave it engaged and you can shift IMMEDIATELY to 4x4 going highway speeds, and leave it out and you have 2wd low range for trailering.

Posilock is probably more reliable, but manual vac CAD has an advantage. Shift xcase and flip the switch and it will go in as soon as the splines line up. With posilock (cable actuated) you have to keep tension on the cable until the splines line up to engage.

I'd say if you don't find a goofy hose going to the CAD, just bypass the CAD switch at the transfer case for now. Leaving the CAD engaged won't hurt anything. You still switch from 4x4 to 2wd at the transfer case. In *theory* it puts more wear on the diff gears and costs a little bit of fuel efficiency, but it's precious little difference in a standard rotation diff up front, which these trucks use. A reverse rotation (like Fords) up front it's more of a penalty due to pushing the "toe" of the gear instead of the "heel" while in 2wd.