BW4404 viscous coupling

[masospaghetti]

Does the transfer case fluid go through the viscious coupler, or is it sealed?

After a fresh rebuild of the transfer case (chain and bearings), I am finding a lot of small metallic particles in the oil, feels like fine grains of sand. This is after driving it about 2 miles. I refilled it again, drove, and drained it with the same result.

Was wondering if there could be debris inside the VC that is being released? Or any other ideas? This was the first time it had been driven with a front driveshaft in years. No abnormal sounds and drove perfect.

96 Explorer 5.0, AWD. Thanks all.

 

[SoNic67]

VC is sealed, it has a silicon-based fluid inside.
http://www.explorerforum.com/forums/showthread.php?t=225515

 

[imp]

Does the transfer case fluid go through the viscious coupler, or is it sealed?

After a fresh rebuild of the transfer case (chain and bearings), I am finding a lot of small metallic particles in the oil, feels like fine grains of sand. This is after driving it about 2 miles. I refilled it again, drove, and drained it with the same result.

Was wondering if there could be debris inside the VC that is being released? Or any other ideas? This was the first time it had been driven with a front driveshaft in years. No abnormal sounds and drove perfect.

96 Explorer 5.0, AWD. Thanks all.

My guess would be that debris is present following some sort of part breakage/failure. It very doubtfully could have come from the VC. imp

 

[masospaghetti]

That's what I was worried about...

 

[SoNic67]

This was the first time it had been driven with a front driveshaft in years.

Now I saw that. Probably your VC is toast because of that. Right now you probably grinding it in pieces.

 

[masospaghetti]

I know this has been discussed before but I don't see why driving w/o a front shaft would do any harm.

There would be a tiny bit of slippage (at most) during acceleration, but the front output would be spinning at the same speed as the rear output and therefore there would not be any further slipping.

Even if the VC was toast, if it was sealed, how would it create metal particles? remember, it drove fine, no binding or anything during turns. I feel like if the VC was toast, I would feel it while driving.

 

[masospaghetti]

OK so after studying that other discussion thread about the viscous coupling, I understand what's going on and how it works.

In the case of running w/o a front shaft, I agree in theory, if the VC provided no initial resistance (if the silicon fluid inside behaved like water, for example) than every time the truck accelerated, there would be a speed differential and the VC would be forced to work and solidify.

BUT it seems like the VC has some initial resistance, even in its liquid state. I say this because when the truck is up on jacks, if you spin the rear driveshaft, the front one also spins. The VC couples them together to some extent, all the time. I think without a front shaft, there's so little load on the front output that the VC doesn't have to do any work at all to get it to spin. The coupling effect of the VC even in its liquid state is enough to spin the front shaft.

That would explain why a bunch of folks who have been running w/o front shafts haven't toasted their VCs.

But back to my original post...a professional shop opened up the case this week to diagnose it for me (I am out of town, so let the pros take care of it). They said nothing looked grossly wrong and that the assembly was correct. The front bearing on the rear output shaft apparently was questionable so they replaced it but they didn't sound 100% sure that would cause the debris. The VC appeared normal, no indication of failure (or self-grinding).

They did say that some debris is normal when new components are installed, esp. a new chain.

 

[SoNic67]

BUT it seems like the VC has some initial resistance, even in its liquid state. I say this because when the truck is up on jacks, if you spin the rear driveshaft, the front one also spins. The VC couples them together to some extent, all the time.

You need to couple almost solidly the front to back in order to FULLY transmit the torque from transmission to rear wheels. Otherwise the torque will be wasted spinning the front stubby in air.
Just that little resistance that can spin the wheels in air is not enough to move a 2 ton vehicle..

For edification, lift the front of a 2WD vehicle (without limited slip, like 99% of them). Start the engine and both wheels will spin. You can stop one of them by hand and you will feel the small torque generated by the slight friction inside the differential. But that is not enough to move the car when the other wheel spins freely (like no CV axle installed there).

 

[masospaghetti]

You need to couple almost solidly the front to back in order to FULLY transmit the torque from transmission to rear wheels. Otherwise the torque will be wasted spinning the front stubby in air.
Just that little resistance that can spin the wheels in air is not enough to move a 2 ton vehicle..

Right, but the VC provides a little bit of resistance even when it's not locked. I'm saying that little bit of resistance seems like enough to keep the front and rear outputs moving together, since the front has no load on it and will essentially follow with little effort.

I understand that if the VC wasn't there, or if it had no resistance when unlocked, it would behave like an open diff.