IntakeRacing

so were sitting around having a couple drinks and we were talking about a truck that came into the shop that had the t-case exploded from the tow truck driving dragging it from the front even though it was in 2wd.


we were talking about this.. how come the front driveshaft always spins even when its in 2wd? but it dosen't put power through...

lol late night beer arguments

OOPS

Because there is no way to unlock the hubs.

vzdude

Even on the trucks that have a disconnect on the passenger side of the axle, the driveshaft still spins because it is connected to the pinion and ring gear, which is connected to the left axle shaft. The transfer case is where the actual power is connected/ disconnected. The third gens without the axle disconnect are the same. It is just easier for it to turn. You could actually hold it still, but then the side gears and spider gears in the differential would be turning wayyy too much and at twice the ratio of road speed.. U-joints are cheaper/ easier to replace.

IntakeRacing

ok i was half right! thanks a lot.

bigdav160

I'm pretty sure that statement is wrong. The axles are connected to the side gears, not the ring and pinion. With CAD, ( '01 and earlier) If the right axle is disconnected then the left axle just spins the other side gear in the opposite direction. There's nothing to drive the ring carrier.

I guess they towed it with the front wheels on the ground? Not good. The transfer case oil pump is driven from the rear drive shaft. Why did Dodge get rid of CAD? Cheaper and less warranty cost would be my guess.

vzdude

O.k. you're right on the side gears. The side gear is still hooked to the spider gears and thus ,the carrier, which is connected to the ring gear, which is connected to the pinion, which is connected to the driveshaft. I was just paraphrasing, but the driveshaft still spins. Like I said...you could hold it and keep it from spinning, but they tend to want to spin. There is less resistance for the driveshaft to spin vs. holding the driveshaft stationary and making the carrier spin .The front carrier is still spinning because there is no way to disconnect the left side axle from it.

Deezel Nate

No your still wrong, it doesn't spin. It might move a tad from time to time, but it's not spinning constantly.

wreedCTD

i believe it does spin.

vzdude

Why do I argue? As long as I know I'm right!
Whatever guys.

BlackSunShyne

Yes, the front drive shaft does spin.

bigdav160

I think we are talking about two different vehicles.

'02 and newer without a Central Axle Disconnect spins the front driveshaft continously.

'01 and older should not spin the front shaft. That is the purpose of the CAD. They might spin "some" only due to friction of the side gears to the carrier case.

vzdude

Get a mirror and look under while you are driving. 2nd or 3rd gen - It spins.

G1625S

Roger that, otherwise you wouldn't have shift-on-the-fly capability. The CAD system is old school and goes back to the high parasitic losses of early t-cases. Dodge should have done away with it far sooner. In any event, you could theoretically stop the driveshaft on a CAD equipped vehicle, but it would put the spiders turning much faster speed. In practice, friction takes over and the path of least resistance is the d-shaft.

bigdav160

Not quite.

When you pull the lever back on the transfer it spins the front drive shaft then the carrier case which causes the right side gear and stub axle to spin the same direction as the left side. Then the vacuum signal from the transfer case actuates the CAD.

vzdude

Not quite! When you engage the transfer case, the driveshaft is already spinning. Also the stub shaft is already spinning as well as the right side axle shaft. Engaging the transfer case engages the gears inside to put torque to the front driveshaft. That is the point that I think most are missing. The driveshaft is spinning, but it has no torque to it. You are right on the fact that the transfercase has a switch that gives the CAD vacuum to engage.