Front driveshaft rotating in 2WD

[gmcman]

I had my wife powerbrake while I was looking at the motor mounts and noticed the shaft rotated slightly... I then had her move it forward and back 4-5 feet and sure enough the front driveshaft was turning proportionate to the speed.

There is no noise or binding while turning, what would be the culprit here, AFAIK, only the CV shafts should turn.

TC fluid changed 50K intervals.

 

[gmcman]

I know this will come up so I went out and checked the actuators.... 2HI to A4WD there is a 2 seond whine in TC, A4WD to 4HI there is an actuation in the front..clearly distinguishable. I did this back and forth a number of times and the front driveshaft is still rotating.

 

[KaRo]

You can diagnose your 4WD System following these steps:
Offroadtb.com Diagnosing the 4WD System

 

[seanpooh]

Well... if I'm understanding what you're saying which is, when the vehicle is moving the front CV shafts that are connected to the two front tires are rotating.

If my interpretation is correct, then the CV shafts rotating is completely normal in 2WD. The CV shafts are splined and held on with a nut on your wheel hub. The inside of the differential is always moving but the ring an gear aren't engaged unless the transfer case puts power into it.

A more conclusive test to ease your mind is to keep the vehicle in 2WD, lift the back end and put it on jack stands. Then give it gas but prepare to brake if you think the front end is engaged. Better yet, lift the whole vehicle. Then you can test out the 4WD while you're there. It'll be safer too...

This will show if your front end has some moving power.

 

[gmcman]

Well... if I'm understanding what you're saying which is, when the vehicle is moving the front CV shafts that are connected to the two front tires are rotating.

If my interpretation is correct, then the CV shafts rotating is completely normal in 2WD. The CV shafts are splined and held on with a nut on your wheel hub. The inside of the differential is always moving but the ring an gear aren't engaged unless the transfer case puts power into it.

Correct, the CV shafts are rotating however this is normal. My problem is the front driveshaft from the transfer case to the front diff is rotating also and not just from the fluidic friction. When I engage D or R there is a quick movement each way just like the rear shaft. The front wheels aren't under torque since the front splined disconnect is not engaged, providing I understand the disconnect correctly.

The front driveshaft should not move when in 2WD.

 

[ByCo]

I doubt that there is anything wrong. The bearings in the transfer case are very good but there is still some small amount of friction that makes the front output shaft want to turn if there isn't any force applied to stop it from turning, plus the lubricating oil in the Tcase also adds a little rotational force through viscous coupling. If you could safely apply clamping force to the front shaft I think you would find the it takes very little to stop it from turning.

 

[gmcman]

I didn't have time to check when I was leaving last night but I climbed under this morning and I could rotate the front shaft by hand.

I guess this is a good thing, I was under the impression the front shaft was completely removed from the circuit in 2WD where even the fluid wouldn't turn it. Perhaps to keep the seals lubricated, not sure but I'm feeling better about it now.

 

[seanpooh]

Yeah, I think the front drive shaft some type of frictional movement but there isn't any power being applied. It might not be an indication to clutch wear since our transfer cases adapt to clutch wear.

I'm not sure I can move mine by hand but... I would have to get back to you if I can or not.

 

[BRomanJr]

I didn't have time to check when I was leaving last night but I climbed under this morning and I could rotate the front shaft by hand.

I guess this is a good thing, I was under the impression the front shaft was completely removed from the circuit in 2WD where even the fluid wouldn't turn it. Perhaps to keep the seals lubricated, not sure but I'm feeling better about it now.

The TC contains a multiple disc wet clutch similar to an Automatic Transmission to engage the front drive shaft. This is one reason fluid changes are so important. The clutch has a residual friction because of the multiple friction plates and steels surrounded by fluid. Unlike an Automatic Transmission, the TC clutch is engaged mechanically by the Encoder, not by fluid pressure on a piston. This all adds up to a previously quoted "around 5%" engagement. In most cases, when truck is shut off in 2WD the front drive shaft can be turned by hand or hands depending on temperature and other factors.

This design allows the "On the Fly" engagement/disengagement to be smooth and quiet since parts are already turning at the proper speed when engagement occurs.

 

[RayVoy]

gmc, after reading all of the posts, I think you are fine.

Normally, the front driveshaft can be turned by hand when the t-case is in 2WD; normally, on occasion, the front driver's side wheel can turn the driveshaft, giving the impression the t-case is turning the wheel.

We have "open" diffs in the front (meaning, one one wheel will receive power when the traction, for both wheels, is not equal. Normally, the disconnect on the passenger side provides an axle with little traction, thus the axle that receives all of the torque. However, when the vehicle is stopped, it is possible for the driver's side to be the axle engaging the driveshaft, shortly after moving, the passenger side will become the axle engaging the driveshaft

BTW, the 5% forward torque is there when the selector is in the AWD (Auto4X4) position.

 

[KaRo]

Good explanation RayVoy! Yes he is fine, i have checked this on mine during the last weekend and it does the same.
Karsten

 

[gmcman]

Good to hear ....the way it was quickly engaging I though it was trying to provide the full amount of torque.