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Viscous Coupling 101

Discussion in '80-Series Tech' started by landtoy80, May 27, 2003.

  1. landtoy80

    landtoy80

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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
     
  2. landtoy80

    landtoy80

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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
     
  3. landtank

    landtank SILVER Star

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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.
     
  4. landtoy80

    landtoy80

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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
     
  5. landtoy80

    landtoy80

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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
     
  6. landtoy80

    landtoy80

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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