Engine/Transmission (1998.5 - 2002) No 4WD. Vacuum leak on CAD System?

[klaybus]

Yep,

My turn. My 4WD isn't working. I checked the vacuum lines at the firewall & followed them across over to the passenger side where they go down & see nothing bad. I know I'm not the first with this problem so where did you find the problem on yours when you had this happen? Thanks in advance for any help on this.....



Clay

 

[wcjp]

On my 96' the problem was at the vacuum lines that attached to the top of the Transfer case. The vacuum lines had stretched. I cut off the bad sections and extended the now shortened lines going to the transfer case. I used small zip ties on every connection. No problems after this.

 

[klaybus]

Thats kinda what I was thinking but with the 2 lo it's even a little more to check. I pulled the block off the transfer case checked all connections & now it's working. Must have been something leaking a bit below but I sure didn't notice anything off. Oh well, working now!



Thanks,

Clay

 

[klaybus]

Been doing some reading online & found this on Dodgeram.org but need a little clarification from someone if they know this system well... . Here are the instructions & I'll post my questions.



Quote"



Shift into 4WD and move truck a couple of feet

If light is still off, park truck, block the wheels, set the park brake, jack right front wheel, and try to hand spin the wheel

If wheel doesn't turn, 4x4 is functioning properly but there is a wiring problem: use an ohmmeter to check the 4x4 switch, wiring, fuse, and bulb.

If wheel turns freely, the front axle or transfer case is not engaged: continue...

Attempt to hand spin the front driveshaft If the driveshaft WILL spin, the transfer case is not engaged Check the transfer case shift linkage, problem is in linkage (or in the tran$fer ca$e internal$ <-- yes this means $$, ouch!)

If the driveshaft will NOT spin, the transfer case is engaged properly: continue...

USE CAUTION! With transmission in neutral or park, start engine, measure vacuum on the two vac lines at front axle shift motor. One line should have approx 20" vacuum, other line should have none.

If NO vacuum measured, look for vacuum leak or bad vacuum switch.

If both lines have vacuum, look for a bad vacuum switch or ruptured CAD actuator diaphragm.

If one line has 20" +/- vacuum:

Move transfer case lever to 2WD, measure vacuum again. Lines should have swapped vacuum signals.

If No: vacuum switch bad or 4WD shift linkage needs adjusting

If Yes: Vacuum motor bad or stuck, or shift fork stuck: continue

Remove vacuum shift motor from the axle, attach vac lines to shift motor, engage/disengage 4WD. Does shift motor plunger move at least 1/2"?

No: shift motor bad

Yes: Check axle shift fork and vacuum motor for binding

Good luck.



OK...

1) From reading this post I believe the vacuum motor is on the right side of the front diff... Correct?

2) Where is the vacuum switch located? Is this the block that attaches to the top of the transfer case?



TIA,

Clay



Posted some pics to help... .

 

[klaybus]

bump... To the top.

 

[klaybus]

OK... Update!

I've got no vacuum at the front axle so I ran a vacuum hose off the engine & attached it to the black port at the axle & woola... . 4WD! Afterwards, I hooked it up to the red port & 4WD disengaged. By my guesstimation, my vacuum switch is screwed up... What do you think? I checked for leaks & have found none. As I understand it, When you shift the transfer case lever it moves a switch in the transfer case & allows vacuum to engage the axle & when it's moved back it switches the vacuum to pull the collar in the axle & disengage the 4WD... I assume this switch is mechanical & inside the top of the transfer case.

Sound correct? This is all i can figure.



TIA,

Clay

 

[Nate]

The vac switch on the T Case is external, it screws into the T case. Inside the T case there is a "rooster tail" that moves when you shift it and that's what controls the vac switch.



Do you have vacuum going to the T Case? Could be something simple as a pinched line and vacuum isn't making it to the T Case.

 

[klaybus]

Do you have vacuum going to the T Case? Could be something simple as a pinched line and vacuum isn't making it to the T Case.



Yep. Got vacuum. I've got Bob V's 2-lo installed so to check for vacuum at the T-case all I had to do is pull a line off my vacuum toggle switch for my 2-lo to check... . I GOTS VACUUM!

Near as I can tell it's gotta be that vacuum switch. I read in another post that it's about a $20 part so if thats the case, it should be cheap & hopefully easy. If anyone has the part number that would be great. I'll update as I know more.



Clay

 

[klaybus]

Fixed!

It was the Switch! I went to Dwayne Lane Dodge in Everett & it sells for $27 out the door. Installed the switch & working GREAT! I traced the vacuum lines & was pretty confident that there were no leaks. As soon as I installed it, I shifted the T-Case into 4WD & woola... ... On came the light. The parts guys said it was fairly common 2nd to leaking lines... Anyhow, 4WD is working again & I'm ready for snow now... .



Clay

 

[EGILLILAND]

Wanted to bump this topic.

Klaybus: If you're still out there... thanks for the troubleshooting guide: AWESOME.

Question for the troops: Anyone successfully "hardwired" the axle into 4x4? We just got hammered by snowfall last night and not having the monster truck to rescue wayward neighbors is becoming annoying.

Any successful hardware methods you have used would be greatly appreciated!

Snowbound in socal...

Eric

 

[LSchulz]

Question for the troops: Anyone successfully "hardwired" the axle into 4x4? We just got hammered by snowfall last night and not having the monster truck to rescue wayward neighbors is becoming annoying.



Any successful hardware methods you have used would be greatly appreciated!

Yes!



The vacuum system went out on mine this winter (found out on a day that was freezing rain and the roads were ice rinks), and I temporarily fixed it while waiting for the Posi-lok parts to come in. Pop the shift fork cover off on the back side of the front axle. There are a few little clips in there that hold the into the actuator shaft. You can pop one of those off, slide the fork over towards the driver side, and then snap the clip back in. Then slide the collar on the splines to the left so that it engages both sides of the axle shaft. Put the cover back on, and the fork will hold the collar in the engaged position. It's not the best long term fix (although it's really no different than the newer trucks without the CAD), but it certainly works.

 

[JMcCoy]

Rip all that garbage out and put in a Posi-Loc cable. If you want strength as well, install a CAD delete axle.

 

[David_VT]

Great thread and still relevant!

http://www.4x4posi-lok.com/app_dodge.html

My vacuum canister hose connections fell off as soon as I touched the dual hose connector. . Guess that explains a bit. . Darn rust!

 

[David_VT]

I did the LSchultz fix above by pulling the switch side C clip and moving the fork into the axle locked position. I reinstalled the C clip so both we're on the non switch side of the fork. I took the truck out into the field for 15 minutes of 4WD horse play with no front end axle fails. I see Genos garage has the proper repair parts but for now I have 4WD!!