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Thread: bad vibration,I have no clue,HELP!!

  1. #1
    Senior Member RACING JUNKIE
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    bad vibration,I have no clue,HELP!!

    Hey guys,I need help again.My car has just rcently developed a vibration.This is how it happened last time I went to the track:

    1st round qualifying: Burnout and pass were fine.No vibrations at all

    2nd round qualifying:Burnout:1st gear ,fine shifted into 2nd,fine,shifted into third,still fine.Just when I was about to let go of the linelock and stab the throttle to roll out I felt the vibration.It felt like severe wheelhop!!

    Car has ladders and coilovers and does not wheelhop.

    Made the 2nd round pass and everything was fine,no vibrations.

    BTW.when I do my burnout,I hold each gear at 4-4500 rpm,until I go to roll out ,which usually hits 55-6000.Going down track I shift at 6600 rpm and cross the line at 66-6800.

    1st round eliminations: Felt the exact same vibrations,at the exact same places as before during the burnout.We went over the car real good betweens round and could find nothing,that is the only reason I wasn't scared to go ahead and drive it,plus it did fine at speed.But,on this pass right before I shifted in to 3rd the vibration started and it was BAD!My car has 4" side pipes that dump right at my door and it is loud,I have seen people in the stands plug their ears when I'm doing a burnout.I wear earpluge just to drive it in the 'hood when I don't wear a helmet.But the
    vibration was bad enough that I could hear seemd like every body panel on the car chattering.It was so severe and steadily getting worse,as I stayed in it,that I just lifted for fear that something would explode.

    But what is it??!!I have checked everything Ican think of.Everything concerning the ladder bars and coilovers is tight and fine.Nothing bent or whatever.Drive shaft and ujoints appear to be un-hurt.Motor and tranny mounts are fine.Wheels are fine and tight.Didn't lose any rimscrews or wheel weights.I even checked to see if maybe an innertube speprated on me :shock: I CANNOT find a thing.The ONLY thing that seems suspect to me is the tranny yoke,it seems to have a little play where goes into the tranny.Just a very little bit,but everyone else that has looked at it says it is the normal amount of play.I figured there would be none????Any suggestions??This one is really working my brain,and I wanna go racing.But,I can't go like this 'cause I'm afraid it gonna shake all my Bondo out :shock: ops: :lol: Thanks for ANY ideas at all Eric
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  2. #2
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Eric,
    You might check the ring and pinion in the rear end? Just a thought. Did it lose a balance weight off of the drive shaft? Did you check the converter bolts? You might have the balance of the slicks double checked for peace of mind, and look for separation.

  3. #3
    Senior Member MASTER BUILDER
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    Eric,

    After checking the things mentioned and rear wheel bearings, another possibility could be that the converter is coming apart on the inside causing it to go out of balance.

    Bill

  4. #4
    Senior Member DYNO OPERATOR
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    First, let me make sure of when this vibration occurs. Just in the burnout, correct? Not down track at all?
    It's entirely possible, that at the fairly low rpm you burout, that it's trying to hookup, and is in fact wheelhop. The times it didn't vibrate, there may have been more water in the box.
    How quick do you run? Any car under 12.00 should have enough power to do a high gear only burnout. Try starting in high and wind it up, say 6000 rpm or so for about 1.5-2 seconds then roll out......
    JMO,
    Johnny

  5. #5
    Senior Member RACING JUNKIE
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    My friend Jimmy Smith had exactly the same problem a couple weeks ago, when running the 7.0 class, it scared him so bad he put it back in the trailer and didn't run. Ladder bar Camero coil over. He checked everything when he got home, ring and pinion, drive shaft, wheels etc. found nothing wrong. It turns out he was rolling to far out of the water box before starting his burnout and the tires were alternately trying to hook and unhook/aka/not enough water for the small motor (355 flattops), i agree you need more wheel speed in the burnout.

    JMO

    Zip.

  6. #6
    Senior Member RACING JUNKIE
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    Thanks guys.Everything in the rearend is new.Gears have less then 5 passes and the whole rest of it has less than20-25 passes.I grabbed the pinion and tried to shake it,thought maybe I wasted a bearing,seems tight.Haven't had the center out but the tires roll freely and I don't hear any unusual noises,or have any extra slack,so I believe the rear is okay.Driveshaft has one weight on it,and it is still there.Marked around it with a paint pen for future reference,she'd still hanging on!Tires and tubes SEEM to be okay,if ya'll know how to check for seperation or anything else to look for,let me know,please.Wasted the tranny and had converter gone thru about 15 passes ago,new bearings and all.Not to say it's okay,but I don't think it would have failed that quick.Balance of tires checks out.I don't believe ot's connected with the balance of the engine,cause it doesn't do it at high rpms.It does it at high wheel speeds.And,YES,it does happen down track.Top of 2nd gear.Car runs [email protected] in the 1/8,3125lb+my fat 240lb butt=slow ops: . Just a thought,my driveshaft is out of a 75 Nova with a 250 6cyl.Was the perfect length!BUT,it is only 2 1/2" diameter AND is a little over 57" long :shock: I wonder if the shaft is just not keeping up?How much weight/power does it take to make a d-shaft "jumprope"?Thanks for the help and keep the ideas coming,I gotta get my hotrod goin'!!
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  7. #7
    Senior Member DYNO OPERATOR
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    Eric, thats a stock driveshaft in the OLDS ,man be careful there not made for what your doing to that car!!!!!May be a problem , inside arent stockers made with an inside tube in em??!! twisty to say the least!! Good luck,Id change that to a cm style driveshaft.KILL 2 birds with 1 stone maybe!!! David,

  8. #8
    Senior Member RACING JUNKIE
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    Yeah,I'm kinda in the process of making the change from street car to race car,it's taking longer($$$$$$$$) than I woulda liked but you know how it goes.Puny driveshaft is why I been holding off on a good converter,too.Just ain't had $400 to lay out for a d-shaft.Not that I mind,that's what I want,just ain't been able to.Oh well,poor me I just wonder if that could be what is causing the problem.I have almost 100 passes on that driveshaft and it's been okay so far,knock on wood.Can't see it doing it all at once.But then again....????
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  9. #9
    Senior Member RACING JUNKIE
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    Oldsy, I got a driveshaft, I had made at Inland for a 54 chevy that might just work for ya. If it will I'll send it to ya, get me the measurements, even if its too long it wont cost too much to have shortened. It's set for a 9 inch and a 400 turbo.
    Earl
    No matter where you go, there you are.
    **IN GOD WE TRUST**

  10. #10
    Senior Member RACING JUNKIE
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    I still have a stock driveshaft in mine too. :?


    Is that internaly balanced or external? I know it's a big chevy but I was thinking it was 496...anyway If it external balance maybe the balancer spun or the weight came of the flexplate? iduno


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