Engine/Transmission (1998.5 - 2002) 4wd not engageing Vacumn Pump?

[jmos4]

Hi,



Got another weird one this morning,



It is rather icy up in MI, so pulled the stick and no 4wd, no light no nothing,



have not had a chance to check the vacuum lines, but do have oil leak at the front of the engine and thought I had read that the vacuum pumps have a tendency to leak, but I could be mistaken so please set me straight if I have it confused



anyone have this happen before



Could it be the CAD going bad?



thanks,

 

[Ram4Sam]

The vac pumps do not fail very often, the pump seals leak quite often but the pump is probably still working. Check all the lines from the vac pump to cad and the hvac controls.



Sam

 

[mwilson]

Hi,



Got another weird one this morning,



It is rather icy up in MI, so pulled the stick and no 4wd, no light no nothing,



have not had a chance to check the vacuum lines, but do have oil leak at the front of the engine and thought I had read that the vacuum pumps have a tendency to leak, but I could be mistaken so please set me straight if I have it confused



anyone have this happen before



Could it be the CAD going bad?



thanks,

How is your heater acting??? Can you switch it to panel, floor, etc.



If not, you have' um big leak somewhere... ... .



Mike.

 

[Ncostello]

Maybe this isn't it... but I've had a similar problem before.



I've seen the shafts get bent on the vacuum powered motors that move the fork in the CAD housing. We had a 3500 at work in which new vacuum shift "motors" wouldn't last a day before the shaft would tweak and jam... rendering everything 4x4 non-functional.



All I did to that truck was disconnect the vacuum lines and cap off with quality vinyl caps (rubber rots). Next I took the CAD cover off, trashed the vacuum motor, and used a 3/8" bolt (if I recall, which fit the shaft hole perfectly) to make a non-movable shaft that held the fork in the "connected" position forever. You have to search a little to find the right bolt length, thread length etc so it will go all the way thru the CAD housing and have threads where you need them for lock nuts, and to secure the bolt itself to the housing.



Its kind of hard to explain exactly what I did to keep the fork in the proper position, but once apart you'll see what you need to make. This forces the axles to remain connected and causes the front driveshaft to rotate 100% of the time while driving... but the transfer case is disconnected internally so its not "pulling" unless engaged. The differential takes care of everything anyway up front... so I figured the CAD was useless except to cause the 4x4 NOT to to work when needed.



We could never actually determine why the shafts were bending. Wear and tear on the front axles was believed to be the culprit. If the splined sleeve didn't engage the splines on the axle perfectly... it may bind and the power of the vacuum motor is enough to bend the shaft quickly. $100 a pop gets old pretty quick.



This continuously locked setup works perfectly and causes no issues summer or winter. Its nice to pull the transfer case lever and have 4x4 instantly. No hoping it engages. Besides Dodge did away with this setup anyhow on 2002's wasn't it?

 

[jmos4]

Hi all,



I checked all the lines and nothing obvious



may buy a hand held vacuum pump to see if the CAD is moving or not when I tear into this weekend



I have heard of the fix of making it permeant 4wd as I did that years ago on a mid 80's axle I had in a truck, though this is the first time I have had one go bad or have issue my gas truck has 200+ and never a issue so can't imagine how this would have one but that's how it goes some times.



I did notice a few weeks ago if I left the 4wd engaged for a long while ever once and a while the dash light would blink not sure if that is part of what is going on now or not



thanks for the advice all

 

[jmos4]

Well it is appearing my vacuum pump died or in the mist of its death roles as my interior vents work only some of the time (switching between defrost and anything else may or may not work only some of the times)



going to sit down this weekend with a vacuum gage and see where I am at but not looking good



is my best option to get a new pump , reman or I have seen soem seal kits on e-bay to rebuild has anyone had any luck with this?



thanks for the input,



Regards,

 

[mwilson]

I still am leaning towards a big leak somewhere, there is not a lot that goes wrong with the pump itself. They fail once in a while, but it is rare.



When you get the MightyMite unplug the line from the pump and start there. You should see rapid vacuum loss when you pump it down, then work your way to the firewall and isolate each line at the big tee.



If you have cruise you may have a big hole rotted through the line right under the battery tray. Very common spot for a leak.



Let us know if you need advice or encouragement (Otherwise known as an "ATTA BOY") over the weekend.



Mike.

 

[pdxkid]

4x4 Posi-Lok Positive Axle Engagement System for Dodge 4x4s



I'm in no way affiliated. I've heard good things, I think I'm gonna pursue this fix.

 

[jmos4]

Hi all,



Well checked out my all my lines and all good, then I checked vacuum psi at, pump, and all tees and then at the axle and was fine so I took apart the CAD, looks like a newer vacuum actuator and was stiff at first after I tore it down and reassemble it worked yet it still after a while at speed 50MPH the 4wd lite blinks, I had a gas truck stick and it never did this, any reason reason or is there something else causing my issues



also my vents seem to be lagging in switching from def to vent to floor not sure if this is related or not may be the electrical box under the hvac, but that I will have to list in another posting



for now the 4wd works yet really considering rigging it full time engaged, just need to flip the side you clip the fork on to do this no bolt need just the dash light will be useless



well thanks for the ideas, if any other on this let me know,



I never had a issue with my 2001 gas for 200,00 mile and my first diesel is not impressing me with reliability thus far, hope it is all coincidence and proves me wrong



thanks again,

 

[mwilson]

Jim,

When the light blinks, is the driveline under strain??? Then when you take away the power the light comes back on???



Mike.

 

[Ncostello]

Having your CAD left in the "connect" position at all times is in no way full time 4x4 or permanent 4x4. All you're doing is making your passenger side axle, from the differential to the wheel, one piece instead of being split in the middle... which was a dumb idea in the first place for alot of reasons.



So kits that manually connect/disconnect the CAD using cables and such, and cost alot... are unnecessary in my opinion. If I had it my way I'd install a solid axle on that side.



The perm-lock kit shown on that website is what I made on my own. The cable disconnect is really only advantageous if you have a spool front or heavy duty locker. Which isn't likely on a street truck or daily driver.

 

[JMcCoy]

The reason for the axle disconnect is to save wear and tear on your u-joints, pinion bearing, spider gears, front drive shaft u-joints, and transfer case front bearing/seal. Also, though minimal, gas milage. I too feel the CAD is junk. I understand why they installed it, but they must have been smoking from their exhaust pipe when they designed the CAD. I have had the Posi-Lok installed for over three years with no problems. When you engage it, its engaged. It also gives you 2wheel low for backing in a trailer. Only problem is that it doesn't address the strength issue with the CAD itself. As long as your not mudding or rock crawling, you should be fine. I had the vacuum diaghram go out because I sucked up water through a leaking vacuum line. You may want to pull the CAD, turn it over, and manually operate it back and forth to push any moisture out. At least a few companies make solid axles to eliminate the CAD. This is the route I am taking. I have already free spun my hubs. Now just waiting for $$$ for the locker, axles, and gears. Hope some of this helps. Good luck.

 

[Ram4Sam]

Hi all,



Well checked out my all my lines and all good, then I checked vacuum psi at, pump, and all tees and then at the axle and was fine so I took apart the CAD, looks like a newer vacuum actuator and was stiff at first after I tore it down and reassemble it worked yet it still after a while at speed 50MPH the 4wd lite blinks, I had a gas truck stick and it never did this, any reason reason or is there something else causing my issues



also my vents seem to be lagging in switching from def to vent to floor not sure if this is related or not may be the electrical box under the hvac, but that I will have to list in another posting



for now the 4wd works yet really considering rigging it full time engaged, just need to flip the side you clip the fork on to do this no bolt need just the dash light will be useless



well thanks for the ideas, if any other on this let me know,



I never had a issue with my 2001 gas for 200,00 mile and my first diesel is not impressing me with reliability thus far, hope it is all coincidence and proves me wrong



thanks again,

Keep in mind that you are having issues with the running gear in a thirteen year old truck, not the diesel engine that is in it... ...



Sam

 

[mwilson]

Jim,

When the light blinks, is the driveline under strain??? Then when you take away the power the light comes back on???



Mike.

Also did you test this with a hand held vacuum pump with the truck's vacuum pump unhooked???



Did you work the heater function from def to vent to floor while hooked to a hand vacuum pump???





Mike.

 

[jmos4]

Well thanks for the input,



I realize this is a older truck my grip is really with myself for totaling my gas 2001, 2500 5. 9 stick I had since new, hence how I ended up with this one and a few more issues than I ever had on my Gas truck not to mention its all new to me so I am very afraid to make a pricey learning mistake as I do not totally understand all the systems on this truck vs the gas one.



I only checked the CAD by blowing lightly on it to get it to move back and forth, I need to get a hand held pump to verify the vents like you all mention



The CAD I had on my gas truck never had issues this one the vote is still out based on what ends up the fix as it has worked for the past few days but still blinks every now and then mostly under acceleration though with no load on the engine it stays lite



I think the CAD was a hope by Chrysler to assist with MPG back when it came out in the mid 80's and in theory it probably was not a bad idea, personally I wish they stuck with front hubs but that is me.



as for bypassing the CAD like I mentioned it merely lets the pass side engaged full time and rotate the rest of the assembly much like the newer ones do as they did away with that in 03 I believe, yes a 1 piece axle would be nice but $$$ the fix I mention will not cost you anything other than gear lube that leaks out to do the change



Thanks again will keep you all posted on what I find maybe the bulb is loose or sensor is bad either way want to be sure I have 4wd before I take off on icy MI roads.



Regards,

 

[mwilson]

If the light is still blinking you have a leak or worse worn splines.



It takes full vacuum to keep the fork all the way over and the plunger on the sending unit depressed.

If it's blinking the fork is sliding back towards the ditch side.



If you don't get it fixed the collar will wear the inner axle down and it will starting jumping out violently when under a load. Then it gets expensive.





I have pictures at home that I will find and post for you where the previous owner of my '97 let a vacuum leak go and go until it simply would not stay engaged under any driveline load.



I replaced the inner axle and shift collar, repaired the several leaks in the truck's vacuum plumbing and it works like a charm.



Mike.

 

[Jeff Knight]

The CAD went away in late 02. My truck was built in Jan 02 and it doesn't have the CAD.



Jeff

 

[jmos4]

Hi,



Update, lite kept blinking and still no signs of a vacuum leak.



so I rigged the front axle locked with a 1/2 nut and 4 washers so the actuator still moves free, and still contacts the switch and to my suprise it does not blink, could it be that the torque on the fork was enough to push against the actuator?



either way it won't chew up the axle now will see how it goes for a while and take a closer look when the weather breaks



thanks again for the info,