Viscous Coupling 101

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The VC or center diff controll coupling assembly as Toyota calles it, is what I think went bad on the old t-case. I did some tests with the VC. I put the VC on the out put shaft and it turns with some effort. I bolted a 3ft bar to it and truned it as fast as I could. I couldn't turn it very fast as there is a lot of resistance but not more than an exercise bike on a very hard setting. I couldn't get it to lock up ( it made me lock up turning it as I am not in shape ). I then got the torch and heated it up as I turned it, when it got hot to the touch, it locked up. When it cooled, it unlocked.The VC is on the rear output shaft. I removed the VC fron the t-case. I could turn the input shaft and both output shafts would turn just like a open diff would. So removing the VC and driving should be a problem unless it us also used as a shim. It didn't look like it is when I looked at it.

I don't know for sure how the VC is suppose to work but this is my theroy:
When driving and all wheels as going about the same speed ( do to turning) the power can go to either the front or rear axle as the t-case is just like a open diff.
When one axle starts to spin, the VC will heat up and lock ( remember there is resistance/friction in the VC and friction = heat). When the VC locks, the diff part of the t-case is bypassed and both output shafts will turn ( like when the center diff is locked).

The other theroy is that only a certin amount of resistance that the VC can spin. Any thing more than that, it semi locks and turns both output shafts.

When I remove the t-case I will first remove the front drive shaft and do some more tests.
kurt
 
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I took off front drive shaft and drove. There is a delay when you accelerate then the vc must kick in and then I move. It must be the second theroy that the vc must spin and grab at a certain rpm. I will check tomorow to if the front output shaft is spinning as I accelerate with then brake on. When I floor the gas in gear there is a delay and then the rear wheels spin (on gravel). I still would like to know if the vc should lock up at a certain temp/ rpm? Should the vc lock up at all?
kurt
 

landtank

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Kurt,
How hot would you guess it was when it locked up? Do you think that was at or around normal operating temps? I still can't imagine any time you would what that to lock up with the ABS active.
 
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When I heated up the vc it was less than a hot potato. So that would be less than normal operating temp. The only time the vc would lock is after driving at 70+ mph. At 60 mph or less it would not lock.
The tires were the same size but worn on the outer tread. They had close to the same tread depth.
kurt
 
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THere is one strange thing with the front drive shaft off. When I put it in drive with the brake on, the suspension will rise up and in R it lowers. It must be all the torgue going to the rear end. The front end must counteract the torque in the suspension.
I feel like one of those wide wheel low riders.
kurt
 
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With the front drive shaft off, the slight viberation niose at about 70mph is gone,
I drove at 70 mph and then went to a gravel parking lot and drove with the t-case locked and unlocked. Unlocked, When I accelerate the motor would rev up and the t-case would slip and then send power to rear wheels and I could spin the wheels. The VC must work like a centrifugal clutch.
kurt
 

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