mattn124

Hello;

For the first time, my truck is starting to have issues going into 4-Wheel-Drive (4WD) and also does not always stay engaged in 4WD.

Not bad for 308,xxx miles!

Looking for advice on upgrading this. My apologies if this thread is in the wrong spot.

I am considering going with one of those kits that removes the CAD stuff and replaces it with a cable. I am thinking of buying this one: 4x4 Posi-Lok Positive Axle Engagement System for Dodge 4x4s

I tried searching the forums for posi-lok, but didn't come up with a bunch of info.

Anybody have feedback on this? I really like the thought of having 2wd-LOW available for backing up trailers.

Question: if I go to this system, will I still be able to engage the 4WD while moving? I have a 45 minute drive to work, so going in/out of 4WD while moving down the road is a very nice convenience.

Thanks in advance for any and all replies!

--Matt

AlpineRAM

I would repair the stock system- it served well for 16+ years and 300+ k miles.

A lot of the troubles with that system are caused by leakage in the vacuum system. Take a look at all the vacuum stuff under the hood (like hoses, connectors, bends etc) an under the truck (Transfer case, front axle) and fix what needs to be fixed and go from there.

2 Low can also be achieved with the stock system and a solenoid, a switch and some wiring.

All the fixes like "posilock" won't help you with other troubles caused by a bad component in the vacuum system. (Had a truck last summer where it was suggested to swap the engine due to blowby issues, the AC system due to having air only to the defrost vents, I fixed it with a 2" piece of hose.... )

mattn124

Thanks for the insights. That is a good point that the factory-stuff has lasted this long so it must be good.

Can you expand on your comment about adding 2-LOW with the factory setup? Is there a thread on here where somebody describes how they did it?

Thanks again,

Matt

AlpineRAM

Basically it is just a solenoid valve that plugs the vacuum line that engages the CAD when activated.

You throw the switch while in 2WD and then shift to 4low, since the line is closed the front axle can not engage.

One of the advantages of the stock system is that it takes care of the timing in the sequence of engaging 4WD for you.
In 2WD the right axle shaft is disconnected and since the front driveshaft is stopped, the inner shaft on the right turns against the driving direction while the outer shaft turns in the driving direction.
When engaging 4WD the transfer case accelerates the front drive shaft with a syncro and then allows the collar to slip in, and that makes the vacuum connection that engages the front axle CAD collar.

With a mechanical system like posilock you would not want to try to engage the front axle while moving before the transfer case has 4WD applied. You would make a lot of shiny chips in the place where the CAD had been.

About fixing the stock CAD- I had some that were quite rusty and also some were full of dirt. Most were fixable by cleaning and lubing them, slap on a new gasket and that's it.

Being thorough on the vac system on these trucks is really important because a leaking hose on the front axle will work like a vacuum cleaner for the road and deposit anyhing it gets in your engine oil pan.

gorms

One vote for posi-lok here. One thing I like about it is you just leave the axle engaged if there is any chance of slippery roads, so shifting on the fly doesnt wear the synchro.

The vacuum system does work, but is not as simple as a cable. I've had to crawl under the truck a couple times because a line pulled off in a snow bank.

mattn124

Thank you all for the great input! I see merits to both plans, either repairing the stock setup or going posi-lok.

Gorms: so if using the posi-lok system; say I pull the cable to "engage" the front axle, can I then just shift in/out of 4WD with the t-case lever? Even while moving as I can now? So, if I had the cable pulled but never threw the t-case lever and tried to make a tight turn on clean pavement (think McDonalds drive thru) would I have my front axle binding up?

If I am understanding this thread correctly; I would NOT want to try and pull the cable to engage the front axle while moving or I would cause damage?


My truck has the "highway gears", 3.54 I think. And with a little bit larger tires to boot, I find myself really wanting 2-LOW for moving trailers around the property. So I am most likely going to either repair the factory system and add the solenoid; or go with the posi-lok kit.

No matter which way I end up going; while I have the CAD removed, is there any other service or maintenance that makes sense to do at this time?

Thanks again to all for your input!!

-Matt

AlpineRAM

With the posi-lock you can either pull the lever before the truck starts to move, and then shift in and out of 4WD as you like while driving. (Just like with the later trucks that do not have a CAD)
Or you can emulate the CAD logic by first selecting 4WD with the transfer case and then pulling the lever.
From then on you can do as stated in the first sentence.

If you pull the posi-lock lever while driving before you have 4WD engaged in the transfer case you will try to connect these 2 shafts that turn against each other at the speed the wheels rotate at that moment without a syncro. Loud noises, metal chips and a hefty parts bill will ensue. So if you are not the only person driving the truck make sure that any other driver understands what the lever is for and how to operate it, or simply padlock it in locked position!

While you are at it I would suggest that you check the bushing that centers the outer shaft against the inner shaft, and your U-joints.(And all the other stuff on the steering and front axle)

mattn124

AlpineRAM: thank you for the explanation. I hate to ask again, but I need to make sure I understand you correctly.

When I say "lever" ---- I am referring to the stick coming through the floor that goes to the transfer-case. I thought that the posi-lok system utilized a cable that mounts under the dash.

That said: I want to make sure I interpret your first couple sentences in your last post correctly.

IF, I am sitting with the truck not moving, and I pull the posi-lok cable to be in the engaged position; can I then go in/out of 4WD by moving the transfer case lever? Can I do this while moving like I can now?

Or, should it be the other way around? (Move transfer case lever to 4WD first, then go in/out of 4WD by working the posi-lok cable).

Thanks again for all the help!

--Matt

AlpineRAM

OK, I was quite unclear there-
All those levers
With the posi-lock you can either pull the posilock before the truck starts to move, and then shift in and out of 4WD with the transfercase lever as you like while driving. (Just like with the later trucks that do not have a CAD)
Or, while moving or not, you can emulate the CAD logic by first selecting 4WD with the transfer case and then pulling the posi-lock
From then on you can do as stated in the first sentence.

If you pull the posi-lock while driving before you have 4WD engaged in the transfer case you will try to connect these 2 shafts that turn against each other at the speed the wheels rotate at that moment without a syncro. Loud noises, metal chips and a hefty parts bill will ensue. So if you are not the only person driving the truck make sure that any other driver understands what the posi-lock is for and how to operate it, or simply padlock it in locked position!

mattn124

Awesome explanation!! Thank you very much for the insights.

I think I'll order the posi-lok tomorrow.

Thanks again,

Matt

KATOOM

This is how the CAD 4wd system works.....

In 2wd the transfer case only gets power from the input and sends that directly to the rear output. The front driveshaft receives no power and does not turn at road speeds. Although it "may" still turn a slight amount while cruising down the freeway just because of internal fluids moving inside the transfer case, but we're only talking maybe 100 RPM at the most.

Also, the front axle on the passenger side is split in two pieces. The CAD unit on the passenger side of the axle housing has a fork controlling a collar which connects or disconnects those two axle pieces. In 2wd the vacuum signal to the CAD pulls the fork to the disconnect side and in 4wd the vacuum signal reverses and pulls the fork to the connect side.

This disconnect of the axle shafts keeps the passenger side tire from turning the differential carrier. That said, the drivers side short axle shaft remains permanently connected to the differential carrier and turns the spider gears. But because the passenger side is disconnected in 2wd, the front driveshaft receives no forces from the differential. In essence the CAD system is acting the same as manual locking hubs but retains the ability to "lock" within the cab so the driver doesnt have to get out of the vehicle.

Now when you shift into 4wd you pull the transfer case lever. This action does a couple things simultaneously:
1) it slides the transfer case shift fork to engage the front driveshaft. But because the driveshaft is NOT spinning at road speeds, it must be brought up to the same speed as the rear driveshaft. This is achieved by a synchro in the TC and acts as a clutch that engages and forces the driveshaft to speed up. This being the number one reason why you shouldnt ever try to engage 4wd at speeds above 10 mph, because the synchro will wear rapidly trying to speed up the front driveshaft to such immense RPM's as the rear is spinning.
2) the second thing happening is the TC has a vacuum switch on the top of the housing which has the job of reversing the vacuum signal to the CAD. That reverse of the vacuum signal pulls the fork as previously described and as the driveshaft speeds up, the differential carrier turns and the drivers side axle and the passenger side axles match speeds which then allows the split axle collar to slide over and connect those two passenger side axle pieces.

Everything working correctly and you not placing too much stress on the drivetrain while switching into 4wd, the whole process just laid out will all happen seamlessly and without noises or clunking.

So all that said..... If you change the CAD unit by converting it to a manual controlled cable operation then as some members have explained, if you dont perform the switch to 4wd in the correct process then you're likely to create damage to either the TC or the front axle. Hopefully I explained that clearly enough and didnt make it even more confusing.

Personally, I'm no fan of the cable design because then you not only have to drill holes in the cab in order to route the cable but its just one more thing to worry about. If the CAD system is in good working order and every component isnt worn or cracked or broke, then shifting in and out of 4wd should never be a problem.

mattn124

Katoom;

Thank you for the excellent write up of how the CAD system works!

I agree that by adding the cable I would be introducing a step into the 4WD engagement process that could be performed incorrectly (causing damage).

But, I really want the 2-LOW option and like the thought of a cable as more rugged than vacuum lines.

There is merit to both. Maybe before I lay down the $$ for the posi-lok, I'll spend some time going over all the vacuum lines.

I'd love to see a write-up from somebody who has built the "solenoid" option and still uses vacuum

Thanks again!

Matt

KATOOM

You're welcome and I'm glad my feeble description was helpful.

As for the 2 lo kit, I should have included that I also have this feature. And yes.....its amazingly handy. I actually find myself using it quite frequently too from either moving trailers around and backing them up, or just getting through an area where 4 lo is too fast. Very nice.....

There are a couple kits but the only one I can think of at the moment is the one Pacbrake has. Its simply an electronically controlled solenoid that reverses the vacuum signal to the CAD so that in 4 lo the CAD fork stays in the 2wd position, thus effectively keeping the front axle disconnected so no power is transmitted.

If I remember right the kits is around $100 and is pretty easy to install. Nothing more complicated than finding a place to mount the solenoid under the hood and where to mount the switch in the cab.

AlpineRAM

I would also strongly suggest to keep the vac system and go with a solenoid.

A: Inadvertently operating the system will cause no damage, and with the right switch you will have a light that tells you that there is no 4WD

B: Any other vacuum problem will be noticed very quickly by you, before the vac pump has caused engine damage.

C: It is cheaper and easier to install.

mattn124

AlpineRam; Thanks for your suggestion about the vac-kits.


I appreciate everybody's input on this topic. I made my choice today and ordered the kit from 4x4 posi-lok.

I see merits to all of the proposed solutions. And this is the route that most appeals to me and how I use my truck.

Thanks!

--Matt