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BAD VIBRATION

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by HAMMERDOWN, Aug 12, 2002.

  1. HAMMERDOWN

    HAMMERDOWN Registered Member

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    Yep-newbie here. Just put in a 14bff in the truck, and I've got a pretty serious vibration. Yes, I've read a ton of stuff here on vibrations, but there is so much, I figured I'd be better off to throw out a post. This vibe feels like its coming from the rear, and it starts shakin between 35 and 45 mph, when under load. Also seems like it wants to start shaking right after switching gears (after shifting into 3rd and 4th in particular). I let off the gas and it stops. Note-this same vibration was happening with my old 12 bolt rear, and it started about a month ago, just outta the blue (drove fine vibe free since 96)-the 14bff is the same shake, but more intense, and more frequent. I replaced both u-joints on rear DS, tires are balanced, TC to tranny is tight, and my cross member is tight. I'm thinking my driveshaft needs balanced (but why would it start shaking out of nowhere with the old 12 bolt & same DS?). Could also be my driveline angle, but I've only got 4" susp. lift, and the angle is not extreme (not much more than the 12b was). Again why did the 12b start vibin out of nowhere? My motor mounts look pretty rough, but if they were the culprit, wouldn't I feel it at idle and rev in neutral? I havn't got a visual on the tranny mounts yet, but I suspect they are in bad shape. Can somebody thro me a bone? Preciate

    JP
     
  2. txbluethunder

    txbluethunder 1/2 ton status

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    try taking the driveshaft and turning it 180 degrees and then bolting it back onto the back axle. sometimes that can make a difference.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    I know this wasn't the original cause, since the problem started before you even touched the driveshaft, but the front and rear yolks are phased, right? (if you've had the shaft halves apart) The front and rear yokes on the driveshaft *have* to be aligned the same way or you can have problems.

    I only mention it in case it ISN'T that way now, but it will help you by eliminating one problem now, if they ARE wrong.
     
  4. BigBluOx

    BigBluOx 1/2 ton status

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    Just to clarify, do you mean the yokes should match front to back when you install the driveline?

    Thanks,
    Jon
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I'm not sure how to describe it...if you picked one cap on one end's u-joint, and drew a line all the way to the other end of the driveshaft, the line should pass through the ear on that u-joint.

    Basically, you can only "mis-phase" a two piece splined driveshaft, and only if the two halves have been apart obviously.
     
  6. BigBluOx

    BigBluOx 1/2 ton status

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    Ok, that makes sense. I think I had some 'brain fade' and was thinking it was possible to have the yoke 'ears' out of phase on a single piece driveshaft... My bad.

    Thanks,
    Jon
     
  7. HAMMERDOWN

    HAMMERDOWN Registered Member

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    My DS is the single shaft slip yoke type, so I believe everything is good to go there (maybe needs balancing, but I don't think so). Crawled under it at lunch to try to find something obvious, and I did find a problem. My transfer case skid plate was rubbing against my TC. Pulled the skid plate and damn if that thing has just about rubbed a hole in the bottom of the TC. It's rubbed all the way through to the bolt located at the bottom rear of the case-I'm sure thats gonna be expensive. Anyway, took it for a drive, and the vibration is not near as bad-still there, but minimal, and nothing like it was. Gonna try rotating the DS 180 degrees and see if that does anything. Might the direction of the zerc fitting on the rear ujoint have anything to do with it? Mine is pointed toward the rear. Any thoughts?

    JP
     

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