2nd Gen Non-Engine/Transmission Front axle not disengaging after using 4x4

[BarryG]

I need some on where to start looking for this problem. When I use 4x4 int he truck wi=hether low or high range it will go into 4wd andthe 4wd light will illuminate. However when I take it out of 4x4 it seems to go into 2wd and the 4wd light will go out. However the front axle is still engaged as I can feel it in the turns. The sharper the trun the more pronounced the binding. It did this last week and it fixed itself after many miles of driving and I think it was actually a really bumpy road that fixed it. I was hoping it was just a fluke. I had to use 4x4 again yesterday. Well it is not a fluke it did it again. I was using 4low and when finished shifted back to 2wd, light went out, it definitely came out of low range but the front axle is still engaged as I can definitely feel the binding during turning.



Any ideas on where to start looking? I assume it has something to do with the CAD but where do I start? The vacumn appears to work as it will engage the axle or at least has been and the switch will turn on the light and going back to 2wd turns the light off and disengages the transfercase yet the axle is still engaged. Anyone have intimate knowledge of how that thing works and can offer advice.

 

[Road Dog]

The 4WD lamp is controlled by a switch on the CAD. So things are moving in the CAD enough to move the switch. The CAD has a sleave that slides over the shaft to connect the axle. The sleave is moved with a fork that's moved by a vacuum actuator. So I'd guess the CAD fork or sleave is broken. Or it's just gummed up and needs a good cleaning. Or there's a vacuum leak (my vacuum line came loose and touched the exhaust making for very slow connect/disconnect). When it's all working it should engage/disengage in under 5 seconds.

 

[Allnew2Me]

When you disengage from four wheel drive, you can put the trans in neutral or back up slightly to release the pressure on the driveline which might allow the CAD to disconnect if it is otherwise sticking.

 

[DieselDoghouse]

As noted above the 4WD lite is activated by a "button" switch depressed when the CAD sleeve pushrod reaches the endof its travel: it will only light when you're fully engaged. It Will extinguish in any other state including degrees of partial engagement—this may be your problem. I would drop the CAD and with engine running to achieve vacuum and some one in the cab to shift, go underneath and observe the shift fork for smooth and positive travel. You can also remove and benchtest using a compressor and LOW (<10 psi) pressure on the opposite port. Then if its OK carefully check all the vacuum lines from the transfer case CAD "valve/switch" (vacuum routing device operated by the shift linkage) Our CAD systems were very poorly designed and implemented IMHO—certainly not a MILSPEC job. The basic function is a vacuum draw always active to the transfer valve, a vent line that admits atmospheric air into the relief side, and 2 outbound switched lines to the CAD which determine 2WD/4WD. Its been my belief that over time the vent line, due to its location close to the road, admits water/moisture into the lines that then accelerates deterioration and leakage—to the point where after CAD #2 I redid my lines in hard plastic (airbrake line) and moved the vent cap high on the firewall like a gearbox vent. So far so good.

 

[EdK]

Front axle

I had similar issues with my '99 this past winter. I push snow with it and I noticed several times I would disengage the 4X4, light went out and (a couple miles down the road) BANG! That was the disengage!



I ordered the 4X4 Posi-Lok system and now I know for sure if things are engagde or disengaged! No more vacuum system with possible moisture/ice issues.

 

[BarryG]

Thanks all for the insight. I just need to get the time to tear into it. It did it again this weekend. Fortunately again I was on some bad washboard/rutted road and after a few miles of that it finally popped out. Of course that wasnt until after 20 miles of slow twisty curvey mountian blacktop road.



Up until the last few times of 4x4 in the last couple weeks it has always worked great goes in and out fine. Truck has 250k on it so while I am not entirely thrilled about this issue I guess I shouldnt be to irked.



For those of you that have dug into the cad are we talking nightmare or no big deal aside from the hassle of just having to do it.



Thanks again for the info

 

[EdK]

Easy Fix

Barry,



It's one of the easier things I have worked on. Except for my laziness not fixing my front seal leak causing oil and crud all over the axle, it's not bad at all.



In fact, the instructions for the Posi-Lok failed to mention the control knob on their unit can be rotated and LOCKED in position. Because of that I had to take the CAD off and on THREE times before I figured out why their adjustment procedure wasn't working!!!



Bottom line... stock unit replacement is a good Saturday afternoon job... two beers or less... still enough time left over to work on the Honey-Do list!

 

[JMcCoy]

POSI-LOK!!! The vacuum CAD is garbage. It will also give you 2low. Moisture in the diaghram will make it fail. Good luck

 

[TRoe]

Sorry for going a bit off topic, but in some signatures, it appears there are trucks of 01. 5 and 02 model year with CAD. I thought some 01 and all 02 trucks were a one piece right side axle like mine. Can anyone shed some light?

 

[PBJ2500CTD]

My '02, mfg date 10-01, has the CAD.

 

[DieselDoghouse]

In some prior posts I've seen reports of problems with the posilock - not dissing it here, just commenting that like any mechanical system there WILL be shortcomings/compromises (my Dad would say no such thing as a free lunch in physics & engineering). With modification I have so far found the CAD reliable—I've just had to make design changes that SHOULD have been anticipated and engineered by any competent design team!!

 

[BarryG]

TROE

I believe it was later 02 models when they switched the cad.



At this point I also want to stick with the cad setup as it has been reliable for me up to this point with 250k miles and no problems. I already have Bob V's 2low kit on it as well.

 

[Jeff Knight]

My truck was built Jan 02 and it doesn't have the CAD. . Jeff

 

[Road Dog]

My truck was built April 2002 and is CADless.

The CAD on my '98 1/2T was fine for 10 years except for the vacuum line touching the exhaust.

 

[WilsonF]

Nothing wrong with the CAD system, I've got 200K miles on mine and no problems. But when it does go I will replace w/ Poai-loc just for the 2W low.

Floyd

 

[JMcCoy]

You are absolutly correct. The Posi-lok is not perfect, but I cannot see the cable failing if it is installed correctly. You just have to run the cable so that it doesn't bind (not hard). No real off roader would use either setup. The Posi-lok doesn't correct the real problem, the CAD. I'm not trying to knock anyone here so I appologize if I offend anyone (disclaimer). We all have different needs. Some of us buy 2wd when we need 4wd and others by 4wd when we only need 2wd. There are also some of us in between. I believe it is better to have it and not need it than need it and not have it. If you need 4WD for extra traction pulling a boat out of the water or some sugar sand on the side of the road, than the CAD (vacuum or cable) is perfect. The problem is for thoughs of us who use the truck to get to a hunting spot, fishing hole back in the woods, of for plowing. Our axles are Dana 44 axles in a Dana 60 housing/tubes. They didn't even give us 35 spline 1. 5" axles. They gave us 30 spline 1. 33" axles. If that wasn't bad enough, they added the CAD with a collar to make the two passenger axles act as one. There is no way to make this strong. The only thing the CAD did was stop the front drive shaft/ring and pinion from moving. The axles, spider gears, axle bearings, u-joints, and axle seals all move and wear out the same. Not only did Dodge get away from this system, even Jeep got away from it. I realize our trucks are not rock crawlers, but we have an enormous amount of weight up front. The cad is just unacceptable for my needs. The CAD has already cost me a transmission (that, a B&M transmission plug, and some water). That is why I will be upgrading to Ford knuckles and spindles. That way I can get out and lock the hubs like a man. No offense to anyone here. Sorry for my rant. It's just a sore subject for me.



I believe the the non-cad axles were on trucks "manufactured" after January 2002. I also believe there are exceptions to this. They used what parts they had left.

 

[DieselDoghouse]

JMcCoy - WELL SAID!! I know however of another vehicle with tremendous axle loading - namely any road-diesel locomotive. I for one am waiting (impatiently) for my coveted chance to own a first (yes I will take an advance issue) diesel-electric pickup truck. Which will then make THIS issue (driveline) as well as traction control, dynamic braking, driveline drag a MOOT point. And…since those phase-modulated traction motors at each wheel will have instantaneous torque-response—I vow to repress the urge to drop the biggest 4-wheel burnout when the light goes green:-laf There are authenticated rumors of such a beast in the pipeline - but I still see drafting tables with empty pages…Git 'er dun!!!