Hacks

[kthaxton]

There's also a minor improvement in fuel economy in 2hi, as the front axle shafts, front differential and front driveshaft aren't turning at all.

With hubs disengaged and in 2wd, the diff and driveline are not spinning on a CAD equipped truck. On the disconnect side of the axle, the outer shaft is spinning. On the non disconnect side, the shaft is only spinning the side and spider gears inside the carrier.

 

[grabinov]

That looks like the 94-01.5 CAD system. With the lack of vacuum pumps since 2004.5 I am guessing the new one is 100% electric, as grabinov mentioned.

Yeah I just went and looked to be sure, but that is the earlier system. My 2014 has a 4-wire electrical connector behind the passenger side of the front axle which is connected to a solenoid and a drive motor. As Kthaxton points out, it makes sense that the system is disconnected most of the time. Why would it not be? If that's the case, then what happens if I simply unplug it and put the truck in four wheel drive or four wheel low? I'm certain I'll get a code, but not so certain as to what else might happen.

The big concern (that is overcome by the manual hubs which people mention and which I had on my last truck - which unlock BOTH hubs) is that while the left to right differentiation is able to occur with the CAD disconnected, there is still no front to rear differentiation. ONE of the front wheels (the driver's side wheel) would likely still be locked to the rear drivetrain, even if the other was disconnected. Since the front and rear axle ratios in most 4wd vehicles are SLIGHTLY different (with the front being a slightly longer ratio) the left front wheel would still want to turn faster than the rears, causing binding and generally bad stuff in the drivetrain. This is why most 4wd's don't even like going in a straight line with the drivetrain locked up.

I'll ask an easier question that we've been trying to solve: Are the axle ratios in our trucks EXACTLY the same? For a fact? I mean FACT. I know we call a 4.10 a 4.10, but I'm not sure that means they are exactly the same in the front and rear.

BTW: I'm not lecturing. I'm actually looking for someone to confirm or correct the above!

 

[JRutzen]

What is CAD?

 

[grabinov]

Sorry. It's the Central Axle Disconnect. Thats' the name that Dodge/RAM gave to the system which locks the front axle when in 4wd. It's an alternative to the old manual hub system, and an alternative to the automatic locking hubs which some manufacturers use. Dodge has always contended that locking and unlocking with a robust central system in one place is stronger than using separate automatic systems with one in each hub. It's been on the trucks since at least 94 (the first time I encountered it) and was originally driven by vacuum with a hose which ran to the axle (and sometimes fell off, disabling 4wd, usually when the axle was already buried in the sand). It was replaced at some point by an electrical system which is present on my '14, but may be in all of the 4th gen trucks.

 

[AH64ID]

CAD isn't just a Dodge thing, several other companies use it and call it CAD as well.

Dodge used CAD from 94-01.5, the there was nothing just a solid shaft to the passenger side until 13 on 3500's and 14 on 2500's. So on my 05 with manual hubs it's a true old school system.

Yes the ratio is the same, look at the drag racers running well up over 100mph in 4wd.

But it doesn't matter, all the front wheel power will go to the tire with the least amount of traction and that is the going to be the half shaft running to the pass side. There will be zero traction to the drivers side.

 

[grabinov]

But it doesn't matter, all the front wheel power will go to the tire with the least amount of traction and that is the going to be the half shaft running to the pass side. There will be zero traction to the drivers side.

Good point. So that means that if I can keep the front axle from engaging, I should be able to use Low gear to tow my trailer from a stop in front of my house up the steep hill to leave, particularly in a straight line. And this is where I started. i just want to know how bad it will be if I disconnect the connector. I respect the complexity of all the computerized systems and don't want to break anything. Just looking for answers...

 

[kthaxton]

Just an FYI, Dodge started using CAD in '85, at least in 1/2 tons and RamChargers. I don't recall for certain, but it was likely 94 for 3/4 and 1 tons.

I do not know what the CAD solenoid will do if it is just disconnected, but I suspect that it won't default to the disconnected position. With the older vacuum system, there was a switch that sent vacuum from one side of the vacuum motor or the other, to engage and disengage the system. The CAD collar would need some type of force to move it each way, I suspect unplugging it may just leave it in whatever position it is in at the time.

As mentioned, if you find a way to control the CAD separately, you would be able to have 2 low without a problem as the inner axle (inboard of the disconnect) will just be spinning backwards. Think of it as just the same as one wheel being off the ground.

I used to live in the mountains with a very steep grade to get to my house. With my tired, 2000 1/2 ton, it had a hard time getting my camp trailer up the grade. I used to just crawl under and reverse the vacuum lines so it would disengage in 4-low, giving me 2-low.

As for gearing, I honestly don't recall how close the ratios are, in reality, it doesn't matter as it is close enough assuming it's stock (example: 4.09 and 4.11 would be close enough).....the main reason it doesn't matter is that 4wd shouldn't be used on high traction surfaces anyway. Even with the perfect ratio, once you turn the steering wheel and move, you'll get binding.


Here's an excellent tutorial:
http://ramchargercentral.com/drivetrain/how-does-cad-work/msg363602/#msg363602

 

[cerberusiam]

In order to fool the electric CAD on the new trucks it will take knowing the range of ohms and volts monitored to insert a control. You cannot just disconnect components or it will go into limp mode and eventually shut down or limit speed. Need an FSM to get the specs on that circuit then a switch, resistor, and power source should be easy to make up to leave it disengaged when 4x4 is engaged.

 

[Bob4x4]

The front axle disconect is actually a module. I haven't had any need yet to diag but it does comunicate with the dtcm.Just guessing it will take a bit of engineering to keep everybody happy.we have tons of rationaliy codes and implausable signal dtc's,i can see the transfer case defaulting to 2wd for self preservation

 

[Bob4x4]

A quick glance I see about a dozen and a half dtc possibilities

 

[grabinov]

A quick glance I see about a dozen and a half dtc possibilities

LOL. Thanks for taking the time to look Bob. That gets us back to where we started. A switch and a resistor aren't going to do it on these smart-trucks. I'm going to need a software engineer who has the capability to interact with the DTCM in order to not only control the CAD but also keep the computer from seeing the change as a failure. I wouldn't be surprised at all if, as Bob says, the DTCM is actually smart enough to lock out 4wd (which BTW is also controlled by an electrical signal, and hence a computer) if it sees what it perceives as a failure of the CAD system. Given that there are numerous companies which have the capability to interact with the DTCM without (mostly) setting codes, it's just a matter of whether any of them is willing to take this on as a programming challenge - i.e., whether enough people would pay for it to make it worth while...