Should I replace missing front drive shaft?

[koda2000]

your front diff is mounted solidly to the truck's frame. since it can't move and the wheels have to be able to turn and move up and down, the cv joint allows for this "misalignment" without changing axle speed the way a u-joint would. i suspect (as i suspected all along) that the previous owner removed the front drive shaft because there is a problem with the transfer case.

 

[delexploder]

That sucks , have you tried to drive it again without the front driveshaft?

 

[delexploder]

If you need the t-case come on down $75.

 

[SoNic67]

i suspect (as i suspected all along) that the previous owner removed the front drive shaft because there is a problem with the transfer case.

Some people also hope that by removing that shaft they will suddenly get 40mpg

 

[imp]

In the awd full time case it acts more like a backwards limited slip, its locked until it gets in a bind then slips instead of letting the bind break something

The viscous clutch is never "locked" mechanically, in any way. It allows for a difference in speed between front and rear axles by "connecting" them together with a "slush" of oil in between, like a mini-torque converter. imp

 

[imp]

Looks like the problem isn't solved after all! AAA just had to give me a tow back home. I was driving down the highway when the truck started shaking violently. I pulled over to the shoulder to see that there was smoke coming out of the CV.

Now I guess the question is was it a problem with the remanufactured driveshaft or could it have to do with the transfer case? One thing I did notice that seemed strange but could be normal is that the CV was at a slight angle to the shaft. Is that whole assembly supposed to be perfectly straight under there?

Not perfectly straight, but the amount of angle ought not to be easily "seeable". Transfer case trouble would not likely cause the truck to vibrate or shake violently, as you describe; a badly wobbling driveshaft (i.e., bad CV joint) could. imp

 

[Flash]

Coming late to the party here.
`
I disconnected the front shaft on my Ltd because the transfer case wouldn't disengage 4wd and caused really bad binding in the front axle.
I suspect your cars previous owner did something similar.

i suspect further that something in the transfer case is causing problems with the CVs.

 

[sulaco83]

I'm going to have to take the shaft off when I get some free time and cross my fingers that I didn't do any further damage.

I think $75 for a t-case would probably be worth the trip down to southern Delaware.

 

[SoNic67]

The viscous clutch is never "locked" mechanically, in any way. It allows for a difference in speed between front and rear axles by "connecting" them together with a "slush" of oil in between, like a mini-torque converter. imp

Wrong. When a NORMAL differential has one end 'open' - like when is missing the shaft - it will tend to spin that side faster and direct all the torque that side. Lift a tire off the front differential (that's not limited slip) and you will see that.
The Viscous Clutch won't engage at all in NORMAL driving. The differential rotation speed on its ends is small (to zero). That's why normal driving will keep the VC liquid cool - front and back axles will turn with same speed (as long as tires have the same size).
When you remove the front shaft, at first it will start spinning very fast, and no power will go to back shaft. Liquid inside VC will heat up and solidify, rigidly locking the front and rear axle (like when front end tire would loose traction). This lock up allows the AWD to move even when the front shaft is missing.
Problem is that this 'lock up' was not supposed to last for long periods of time. Driving years with the VC inside TC heating it will eventually permanently damage the fluid inside (silicon based), and will harden more that is supposed to be.
Adding the shaft now adds back the requirement for differential functionality, and locked-up VC opposes that. Is not a solid lock, so some friction will happen inside VC.
Hence the heat, the noises...

 

[delexploder]

Sulaco83 I left you a visitor msg in your profile area

 

[imp]

Ford's viscous clutch

Wrong. When a NORMAL differential has one end 'open' - like when is missing the shaft - it will tend to spin that side faster and direct all the torque that side. Lift a tire off the front differential (that's not limited slip) and you will see that.
The Viscous Clutch won't engage at all in NORMAL driving. The differential rotation speed on its ends is small (to zero). That's why normal driving will keep the VC liquid cool - front and back axles will turn with same speed (as long as tires have the same size).
When you remove the front shaft, at first it will start spinning very fast, and no power will go to back shaft. Liquid inside VC will heat up and solidify, rigidly locking the front and rear axle (like when front end tire would loose traction). This lock up allows the AWD to move even when the front shaft is missing.
Problem is that this 'lock up' was not supposed to last for long periods of time. Driving years with the VC inside TC heating it will eventually permanently damage the fluid inside (silicon based), and will harden more that is supposed to be.
Adding the shaft now adds back the requirement for differential functionality, and locked-up VC opposes that. Is not a solid lock, so some friction will happen inside VC.
Hence the heat, the noises...

Look, I don't care to get into a pissing match to prove one or another right or wrong. I have scanned the description of the viscous clutch right out of the FORD SHOP MANUAL; it's below. Read it. The clutch contains no variable-viscosity fluid. It does not act based on heat at all. Where do you draw the information from which you presented above in such great detail? SOME of what you say is undoubtedly true; excess heat build-up WILL damage these damned clutches, I'm sure.

Some folks here may want or need to know what's really going on with these "complicated" devils. That's why I presented it in a simple form in my post-- simple description, but adequate for the novice to see what's happening. imp

 

[masospaghetti]

When you remove the front shaft, at first it will start spinning very fast, and no power will go to back shaft. Liquid inside VC will heat up and solidify, rigidly locking the front and rear axle (like when front end tire would loose traction). ...will eventually permanently damage the fluid inside (silicon based), and will harden more that is supposed to be.

How can this be? The specified fluid is standard Mercon ATF, and I know ATF doesn't solidify with heat.

 

[koda2000]

How can this be? The specified fluid is standard Mercon ATF, and I know ATF doesn't solidify with heat.

the 2 qts of Mercon ATF lubricates the moving parts in the transfer case. there is some sort of viscous coupling (none serviceable) which allows the necessary slippage for the AWD. if you've ever tried to drive a true 4x4 on dry roads in 4WD, you'll notice it doesn't want to turn. this is because all 4 wheels are turning at the same speed. i'm no expert on the viscous coupling, but from what i've read on this forum, when they go bad they seem to lock up.

 

[imp]

Re-GROUP!

How can this be? The specified fluid is standard Mercon ATF, and I know ATF doesn't solidify with heat.

See my post #31. Now, I gotta back off a bit. First, you're right in that ATF is like any other type of petroleum-based oil; it gets THINNER as it gets hotter, and the transfer cases use ATF as their lubricant. BUT, the viscous clutch is a SEALED UNIT, which operates within the transfer case itself, so it could be filled with almost anything, the two fluids only mix if the seal on the clutch FAILS.

Since I posted the Ford blurb about them, I found several articles indicating that the clutch IS filled with a negative-viscosity coefficient fluid which thickens as it gets hotter. These articles may or may not be accurate, like anything else submitted to the internet by "experts".

So, I concede that the clutch COULD be filled with heat-sensitive fluid. It's even possible that Ford has used them both ways, but that seems rather doubtful as the chances for mix-up would be great. At this point, unless someone can get verification from Ford Engineering, I'll just say this: If the torque-delivery "split" between front/rear wheels is 35%/65%, the difference is explainable as HEAT generated within the clutch. My belief that it functions similarly to a small torque converter, more accurately, a non-torque-multiplying fluid-coupling, stands, at this time. Just as in a torque converter, where the input speed (engine) is greater than the output speed, of the fluid-coupling, (transmission input speed) so goes it in the viscous clutch. imp

 

[imp]

the 2 qts of Mercon ATF lubricates the moving parts in the transfer case. there is some sort of viscous coupling (none serviceable) which allows the necessary slippage for the AWD. if you've ever tried to drive a true 4x4 on dry roads in 4WD, you'll notice it doesn't want to turn. this is because all 4 wheels are turning at the same speed. i'm no expert on the viscous coupling, but from what i've read on this forum, when they go bad they seem to lock up.

This is true. They can also have seal failure, in which their fluid leaks out, and mixes with the transfer case fluid. When that happens, the viscous clutch no longer transmits any power. imp

 

[delexploder]

Like I said it works like a limited slip

 

[koda2000]

This is true. They can also have seal failure, in which their fluid leaks out, and mixes with the transfer case fluid. When that happens, the viscous clutch no longer transmits any power. imp

well if mine ever fails i hope in fails in this way...lol. i never wanted the AWD feature anyway. the truck was advertised as RWD (which is what i prefer) and while i checked the truck over pretty well, i trusted my so-in-law's answer when i asked if he saw any front axles while he was looking at the ball joint boots (which were of course torn). oh well, 7 months and no problems with the AWD yet. AAA will be towing the truck to my house tomorrow, as my daughter ran over something in the road ruining a tire and maybe taking out a transmission line (at lease i hope that's all i find).

 

[imp]

well if mine ever fails i hope in fails in this way...lol. i never wanted the AWD feature anyway. the truck was advertised as RWD (which is what i prefer) and while i checked the truck over pretty well, i trusted my so-in-law's answer when i asked if he saw any front axles while he was looking at the ball joint boots (which were of course torn). oh well, 7 months and no problems with the AWD yet. AAA will be towing the truck to my house tomorrow, as my daughter ran over something in the road ruining a tire and maybe taking out a transmission line (at lease i hope that's all i find).

So thus far, the AWD has been satisfactory for you! If you read the Ford blurb I posted, it says (I think!) the viscous clutch INPUT, in other words, driven by the engine, connects to a "front planetary gear assembly outward to the ring gear to the upper output shaft". I'm reading that the clutch input side turns the "upper output shaft" (this must go to the rear wheels, I think). Now, going on, "torque also flows through the front planetary gear assembly to the overdrive sun gear outward to the upper drive sprocket". The upper drive sprocket obviously drives the chain, which then drives the front wheels through the front driveshaft. So, between the "upper output shaft" and the upper drive sprocket, we have the fluid in the clutch driving the upper drive sprocket (front wheels). Are you with me? If I'm barking up the wrong tree, let me know it! There is a planetary gearset involved here which would seem redundant. There can be NO gear reduction between the front and rear wheels, as they are always trying to turn together in a four-wheel drive.

I disputed from day one, that the AWD could allow the vehicle to "creep" when the transmission is in "Park". Those more knowledgeable than I insisted that they do creep. I THINK, this occurs because of the presence of the planetary gearset. Maybe it's time I sit down with the entire transfer case break-down in front of me, and try to figure all this **** out!

Anyhow, what you said at first: it looks like if the fluid leaks out of the viscous clutch, you will not be driving like a RWD, actually the vehicle won't move (I think!). Anyone know the answer to the leak-out puzzle? imp

 

[koda2000]

So thus far, the AWD has been satisfactory for you! If you read the Ford blurb I posted, it says (I think!) the viscous clutch INPUT, in other words, driven by the engine, connects to a "front planetary gear assembly outward to the ring gear to the upper output shaft". I'm reading that the clutch input side turns the "upper output shaft" (this must go to the rear wheels, I think). Now, going on, "torque also flows through the front planetary gear assembly to the overdrive sun gear outward to the upper drive sprocket". The upper drive sprocket obviously drives the chain, which then drives the front wheels through the front driveshaft. So, between the "upper output shaft" and the upper drive sprocket, we have the fluid in the clutch driving the upper drive sprocket (front wheels). Are you with me? If I'm barking up the wrong tree, let me know it! There is a planetary gearset involved here which would seem redundant. There can be NO gear reduction between the front and rear wheels, as they are always trying to turn together in a four-wheel drive.


I disputed from day one, that the AWD could allow the vehicle to "creep" when the transmission is in "Park". Those more knowledgeable than I insisted that they do creep. I THINK, this occurs because of the presence of the planetary gearset. Maybe it's time I sit down with the entire transfer case break-down in front of me, and try to figure all this **** out!

Anyhow, what you said at first: it looks like if the fluid leaks out of the viscous clutch, you will not be driving like a RWD, actually the vehicle won't move (I think!). Anyone know the answer to the leak-out puzzle? imp

from what i understand, they can creep/drift in PARK with the front drive shaft removed because of the PARK works with the AWD. from what i understand PARK is split like the torque, that is to say 35% to the front wheels and 65% to the rear. i'd love to take one of these transfer cases apart and study it (but if i never have to that's okay too). i really like knowing how things work, especially things that don't make sense to me. in the meantime, i've repaired the parking brake on my AWD just in case it *****-to-bed and i have to remove the front drive shaft.

 

[imp]

Creepers!

Koda, I just gotta know, too, just the same as you! My lurking through all these AWD posts indicates the AWDs creep in Park even with the front shaft installed! That's what made this all so hard for me to swallow. There were Technical Service Bulletins (TSBs) shown from Ford, indicating creeping was normal.

I felt, if Park doesn't work, why leave the unsuspecting driver to find his vehicle slid down a hill in Park, because he did not engage the parking brake.

I had a '99 Explorer which had been wrecked, bought it reasonable, 5.0L w/AWD, fixed it up & sold it, but never tried the creep thing, didn't know about that at all back then. imp