Testing Viscous Coupler with Automatic Transmission

Testing the viscous coupler with a standard transmission consists of raising all 4 wheels off the ground, then starting the engine, putting the car in gear, letting the clutch out with the engine idling and setting the e-brake. If the engine dies, the VC is good, if it slows but then recovers, the VC is bad.
With an AT, the engine won't die with the drive-train locked up. So, how does one test the VC with an AT?

After giving this some thought, I THINK I may have the answer. Performing the same test with an AT should cause the front wheels to stop rotating along with the rear if the VC is good. The engine will do exactly the same thing it does when you use the brakes to stop the car while in drive.

Has anybody performed the VC test with an auto? What were the results?

Comments

  • I put mine up on jacks and let it run and all 4 wheels turned. I think I could easily stop the front right and rear left though while it was in idle.

    I didn't try any e-brake tests. I can do that this weekend though.
  • I believe you are correct. If the VC is good it should transmit the braking power at the rear to the fronts and stop all wheel rotation.
    MrWhoopee wrote: »
    After giving this some thought, I THINK I may have the answer. Performing the same test with an AT should cause the front wheels to stop rotating along with the rear if the VC is good. The engine will do exactly the same thing it does when you use the brakes to stop the car while in drive.
  • This works because of the open diffs. A weak VC would behave the same way.
    superhatch wrote: »
    I put mine up on jacks and let it run and all 4 wheels turned. I think I could easily stop the front right and rear left though while it was in idle.
  • superhatch wrote: »
    I put mine up on jacks and let it run and all 4 wheels turned. I think I could easily stop the front right and rear left though while it was in idle.

    I didn't try any e-brake tests. I can do that this weekend though.

    Yes, when one wheel spins free, no power transmits to the other. It is when both wheels have grip that things start to move.
  • This all occurred to me because I just bought an '06 Toyota Matrix AWD with AT. It uses a VC drive-train which is similar to the RT. I asked the question here because no one in the Matrix/Vibe forums has a clue. I tested it today while having the snow tires installed. When I engaged the e-brake, the front wheels stopped spinning momentarily, then resumed spinning, but very slowly. That tells me that the VC is weak but functioning. I see a rebuild in my future.
  • HaydzHaydz Moderator
    https://www.civicwagon.com/showthread.php?7979-Viscous-Coupler-info

    This thread doesn't suggest a different test for AT and the info is taken from FSM. Perhaps we just confirm this by looking at the FSM again.
  • My 1991 FSM only has one section about testing the VC and it only for the MT.
  • Here is a quick photo of the FSM. This is Section 16 "Propeller Shafts" It is after the MT and AT section.

    186.jpg

    About the AT and setting the parking brake, it might not take much torque to overcome the torque converter. I would set the parking brake and see if all wheels stop and if they do I would give it a little throttle to load the VC harder. Should give you some idea of how tight the VC is.
  • Yup, that test is obviously for a standard trans. Odd that they made no mention of testing with an AT.
  • Follow-up real-world testing on the Matrix. With a fresh 4 in. of snow, I tried to climb my driveway (unpaved and way too steep for fwd when there's snow) and my neighbor's driveway (paved and even steeper than mine). It motored right up both without hesitation or tire spin (with studded snow tires). Perhaps the slippage I saw was by design, less than 50/50 power distribution.
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