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Thread: Driveline Vibes - Please Explain

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    Question Driveline Vibes - Please Explain

    So some of you may have seen me asking questions about getting out the stud from my TC crossmember, however I was wondering if anyone could clarify driveline vibes for me.

    I have minimal vibes on acceleration, and then everything is smooth after 80kph.

    At ANY speed, if I hit the brakes even at a "normal" pressure, I get a very bad vibration that I can feel through the floor. It almost sounds like something is binding. It goes away only when you stop or accelerate away again. The harder you brake, the worse the sound/vibes are. If you coast to a stop or brake very lightly the XJ can be stopped without this excessive noise/vibe.

    Second, when travelling at a constant speed, I can hear a slight "bffft" vibration when I lift my foot off the gas, and then the same slight sound when gas is reapplied. The noise is only for an instant, however if you 'feather' the gas pedal just right you can keep the "bffft" sound going.

    From what I have read, the vibe on deceleration is fairly common. Just wondering what exactly is the cause of the excessive noise when stopping... I can live with the other vibes, but this deceleration noise has got to go!
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    I have the deceleration noise as well. I also have no idea what it is though. I have learned to live with it, as mine isn't that bad.

    I would check your hubs, and axle shaft u-joints for your speed wobble.

    I also have the "bfft" noise when taking foot off gas or when first applying gas. The only thing that I can think of for this is, maybe the rear pinion yoke, or driveshaft u-joints.
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    Most of the lift kits tell you to tweak the rear pinion angle one way if you get vibes on acceleration, the other way on decelleration.

    My only concern is that your DS might be binding just a bit (yokes touching) during decelleration when your rear end is lifted up... that would be bad.

    Tweaking the pinion angle will only help if it's the rear joint binding, and I think the normal problem is at the front. Did you end up dropping your tcase or are you still fighting that broken stud ?

    Disclaimer -- I have no idea how to set the rear pinion angle on an XJ

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    I haven't dropped the tcase yet.. hopefully on Saturday.

    Someone else mentioned that it might be the front driveshaft U-joints, and I've noticed that I can get the sound worse if I engage 4WD. It does sound like it is coming from the front.

    The bfft I can live with, the normal vibes I think will be solved by lowering the TC. I can only hope that the front goes away as well.

    Maybe some already worn front u-joints are being made worse by the lift?

    What do you mean by "your DS might be binding just a bit (yokes touching) during decelleration"? Do you mean the yokes contacting inside the TC? How would a lift do that, since doesn't lifting actually pull them farther apart from the TC?

    EDIT - just re-read.. you mean driveshaft binding? I looked earlier and didn't see any wear, but where exactly should I be looking? Its hard to check the noise when travelling at 80kph!
    Last edited by TopherTJ; 04-23-2004 at 02:08 AM.

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    is it at all possible its in the brakes?

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    Sorry.. forgot to update.

    Got the TC dropped an inch and no more vibrations. It was definitly the front of the rear driveshaft contacting yokes. The drop sits everything nicely now and I can hammer on the brakes without any vibrations.

    Sure, I lose an inch of clearance byt $10 at Home Depot is still cheaper than a Slip Yoke (for now!)

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    >>It was definitly the front of the rear driveshaft contacting yokes.

    That's the same problem my Rubi has -- yokes touch at the tcase end of the rear driveshaft unless I drop the tcase.

    Glad it's all working for you. Just curious, do you have a 5 speed or automatic tranny ?

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    Auto... thing is it was difficult to figure out. It made a difference on how you parked. Mostly the yokes were far apart and looked normal, but once I guess the rear didn't settle as much and I could see that they were touching.

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