will AWD Driveshaft d/c roll away?

Glen4X4 · January 13, 2008

Ok there is this guy thats having problems with his explorer and its a 5.0 awd and he wanted to know if it's ok to just disconnect the front driveshaft from the t-case, and people are saying that if he does so, that his truck will roll away in park and cause damage to the t-case I never heard of something like this, so wanted some input from people that actually own one or know the mechanics of it.

storlied · January 13, 2008

The AWD parks through the front, no damage should be done unless it hits something while rolling away.

Glen4X4 · January 13, 2008

K thats what I was looking for, he wanted to disconnect the front driveshaft and drive it that way.

storlied · January 13, 2008

Why though? Gas? Performance? It sure isn't for better traction.

Glen4X4 · January 13, 2008

No he said a noise was going on in the front end when towing and even sometimes when not towing. So he wanted to see if disconnecting would make noise go away and to further diagnose the problem

storlied · January 13, 2008

Tell him to be careful.

Glen4X4 · January 13, 2008

alright thanks for the input.

MountaineerGreen · January 13, 2008

For diagnostic purposes only- its been debated back and forth, but since the tcase splits power front to rear, your are using power to spin the front output for nothing. It will roll in park and could possibly damage the viscous coupling in the transfer case. I personally wouldn't risk it.

Glen4X4 · January 13, 2008

2 other people had told him that it would roll away and one said that something in the t-case could burn up, I knew it wasn't exactly like a 4X4 t-case since it splits power but also didn't know if it actually hurt disconnecting it so before I said anything I wanted to ask here so I wouldn't be the reason for any further damage being done to his truck.

storlied · January 13, 2008

If he's only driving it for a very short time at a low speed to diagnose a problem, it shouldn't cause any damage.

Dan Whitaker · January 14, 2008

He wouldn't happen to be a member on Ford Truck Enthusiast would he? I answered a question there today exactly like this one.

reserved50 · January 14, 2008

I've had mine roll way at least twice, once I forgot and rolled into a parked car, the other time I did I have e-brake on (I guess the park shoes were toast) and it blocked traffic because I was hoping the cranked wheel would stop it, yea it only works if its close to the curb haha

. Guy at Ford said an engineer told him not to drive it with no front shaft, I put on 1000kms with no shaft obviously not listening to advice and it seems to have cleared up my front end binding on turns problem after I reinstalled it

.

95Blitz · January 15, 2008

The AWD doesn't park through the front drive shaft. If it did there would be a linkage from the shifter to the transfer case. Plus my front drive shaft is out and when I put it in park it doesn't roll away. Its locked in park. The trans locks the output shaft in park and that locks the transfer case and both drive shafts or in my case the rear drive shaft.

sparkyXplorer · January 15, 2008

Well yes it does park the Trans but since the Awd case is the "searching for design style in my head, but can't think" but without the front drivshaft it will not park securely...it will park on flat ground but I could not park mine on my drive way prior to doing my 4406 swap when the shaft was out. and one time in my garage I was working on bolting down my sub box and I was pushing hard against the box to get it as close to the back seat as possible and when I went to open the garge it hit the bumper.

IZwack · January 15, 2008

95Blitz said:
The trans locks the output shaft in park and that locks the transfer case and both drive shafts or in my case the rear drive shaft.

Nay .. even with the transmission in Park, the vehicle can still roll away because of the viscous coupling which is the core of the AWD transfer case. Plenty of people on the forum have had their AWD 5.0L vehicle roll away in Park.

So a word to the wise for all the 5.0 AWD users, if you must remove a driveshaft, set the parking brake and block off the wheels (in case the parking brake is worn and can not stop the weight of the vehicle).

Dan Whitaker · January 15, 2008

95Blitz said:
The AWD doesn't park through the front drive shaft. If it did there would be a linkage from the shifter to the transfer case. Plus my front drive shaft is out and when I put it in park it doesn't roll away. Its locked in park. The trans locks the output shaft in park and that locks the transfer case and both drive shafts or in my case the rear drive shaft.

Then it's on completely flat ground. If you remove the front drive shaft IT WILL ROLL. When I replaced the front drive shaft on my '97 Mountaineer in Nov '06 I had it up on ramps. As soon as I unbolted the front drive shaft it started rolling down the ramps.

Read the post in this thread by others that have removed the front drive shaft and stated it rolled.

sparkyXplorer · January 15, 2008

"viscous coupling" thats what I was looking in my head for...thanks

gijoecam · January 15, 2008

Indeed, it can and will roll away if the viscous coupling is working as it should. The transmission is locked in park, but the transfer case allows the slippage without the resistance of teh front driveshaft/drivetrain.

AWD owners should also note that the danger jacking one tire off the ground presents the same hazard when changing a tire.

-Joe

justin146 · January 15, 2008

Ok, explain this to me...

I was under the impression that there was a solid connection from the input of the transfer case to the output for the rear driveshaft; and a chain off of this goes over to the viscous coupler unit on the front driveshaft. IF this is so, even if there was no driveshaft, there is still a solid connection from the output of the tranny to the rear axle. The only slip point is on the front axle output.

can someone post an exploded diagram of the transfer case?

gijoecam · January 15, 2008

The pictures don't copy and paste here, but here's the text from the service manual:

The constantly activated, automatic, all-wheel drive transfer case has no external controls. A two-piece aluminum case houses the assembly. The unit is chain driven. A non-repairable viscous coupling provides torque distribution to the front and rear transfer case outputs. The viscous coupling contains slotted alternating plates through which a high viscosity fluid flows. The resistance of the fluid shear causes the plates to transmit torque at the approximate ratio of 35 percent to the front output and 65 percent to the rear output.

Operation

Torque flows through the input shaft to the front planetary gear assembly outward to the ring gear to the upper output shaft. Torque also flows through the front planetary gear assembly to the overdrive sun gear outward to the upper drive sprocket. The torque flow continues from the upper drive sprocket through the drive chain to the lower drive sprocket to the front output shaft. The viscous coupling provides the connection between the ring gear and the overdrive sun gear.

From the pictures, I can tell you that there does not appear to be any direct mechanical link between the rear output and the input. The input drives the VC which drives both outputs proportionally.

The experience of those owners on this board confirms that. I have not personally had one apart to see what makes it tick, although I've been wanting to tear into one for years. My rudimentary understanding is that it works similar to a limited slip differential of sorts... it drives an intermediate assembly (in the case of a diff, it would be the carrier) which then distributes the torque to the two potential outputs. It does not drive the rear wheels directly.

will AWD Driveshaft d/c roll away?

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