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  1. #1
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    May 2018
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    Steering Scrub At Full Lock Either Left or Right

    X4 Sport Kit built by me around 5 months ago. No problems during the build or to date.

    Problem: When turning the wheels full lock either left or right on an otherwise stock X4 there is a bit of what some people call steering scrub. At full lock and while moving, it feels like there is some binding and then releasing taking place in the front axle. It's worse as speed increases. Otherwise no problems with the drivetrain, servo, esc, tires, wheels, hubs, axles, shocks, etc.

    I've heard others complain about the same issue. The steering endpoints are no where near maxed out and there is no binding that can be found anywhere in the drivetrain. At full lock there is clearance between the portal cover and the steering yoke. CV's are good. Lubrication is good and assembly has been verified over and over. I'm pretty skilled mechanically so I'd like to think that if it's a noticable problem that I would have found it by now after several hundred hours of crawling with my X4. Also, it has done this since the very start after I built it.

    Is this perhaps a portal axle geometry thing, a portal axle CV joint geometry thing, or something particular to the X4?

    BTW: Searched back to 2017 and found nothing.

  2. #2
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    This is completely normal on a vehicle with locked differentials. When turning, the wheels travel different distances, and without open differentials to compensate for this the inner and outer wheels (and also front/rear) "fight" each other resulting in tire scrub.
    The TRX-4 versions with lockable front and rear diffs also have this "feature" due to the lack of a center diff. But on these versions it's not as severe when the front and rear diffs are open.
    Last edited by Viking; 08-07-2019 at 12:38 AM.

  3. #3
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    May 2018
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    So, on the X4 Sport, without the locking diffs (and the single speed transmission), I wouldn't think that this would be so much of a problem. I've got the stock gears in the front diff and underdrive gears in the rear diff.

  4. #4
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    The Sport models have spools instead of working diffs. This is the same as locked diffs - hence the tire scrubbing.
    The underdrive on the rear will probably reduce the push from the rear a little when turning.

  5. #5
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    May 2018
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    Ah, I'm learning. Thanks for the details. This explains why my friends X4 does not suffer as much from the scrub steer. He has both over and under drive on his.

  6. #6
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    Yep, that sounds like a likely explanation. Glad to be able to help!

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