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Excessive driveline play/ is this the "cobra clunk" (videos inside)

Discussion in 'Driveline' started by CarolinaCobra, Mar 8, 2011.

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  1. Fast GTO

    Fast GTO Member Established Member

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    That causes the play? The noise I am aware of and not bothered by. Is this something that would cause damage?
     
  2. keith89

    keith89 Well-Known Member Established Member

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    I believe so. I did some searching on truetrac clunk and it seems to be hit and miss. Some mustangs with truetracs are quiet others clunk. The same goes for other cars with truetracs installed. I don't know if my shop put in synthetic(which should not be used with the truetrac) but I'm going to drain it out and put in fresh redline heavy duty shock proof oil. I've heard this absorbs some of the shock and reduces noise.
     
  3. Fast GTO

    Fast GTO Member Established Member

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    Eaton says to use stock gear oil....and I've been told synth is fine. Not sure how that would cause the play in the driveshaft. Noise sure, but play, not convinced.
     
  4. Fast GTO

    Fast GTO Member Established Member

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    Well, Bob Kurgan took a look at the vid and said it was normal driveline play.
     
  5. keith89

    keith89 Well-Known Member Established Member

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    the gear oil doesn't solve the play it dampens it. I have to find the instructions to my truetrac. I'm pretty sure it says not to use synthetic. I've also read multiple instances where synthetic cause the truetrac to increase noise when the worm gears are winding out.
     
  6. TRQJUNKIE

    TRQJUNKIE Justa Slobra Established Member

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    I always told myself that noise was all those big horsies trying to get to the ground.
     
  7. CarolinaCobra

    CarolinaCobra New Member Established Member

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    I don't know how I feel about this. I mean, I trust the guy and I certainly believe him but I really was hoping there was something wrong. I would gladly pay to get this fixed.
     
  8. Fast GTO

    Fast GTO Member Established Member

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    I dunno, just reporting what I was told.
     
  9. ludbg

    ludbg New Member Established Member

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    i got just as much play but my differential also whines when cruising. when i let off the gas it stops and when im in neutral it stops.
    but the play cant be normal when im shifting fast there is a big BANG every time...

    wouldnt an lsd fix that?
    http://www.americanmuscle.com/ford-racing-88-lsd-28spline.html
     
    Last edited: Mar 17, 2011
  10. 06cobradreamer

    06cobradreamer New Member Established Member

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    I'm willing to guess your problem might be like the SRA guyz experience.....
    C clip slack/wear.
    and Truetak wear (collection of things)

    There are many reasons to use c clip eliminator on SRA (I have them as well) slack/slop is one, axle breakage, axle coming out completely while drive etc.

    not the same reasons for the IRS stuff but the slack would be an issue like the video is showing, not sure about a clip eliminator for the IRS though, ,,,, more homework is needed
     
    Last edited: Mar 17, 2011
  11. Fast GTO

    Fast GTO Member Established Member

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  12. BIGV

    BIGV GO BIG OR GO HOME!!! Established Member

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    Op mine has the exact same amount of slack my clunk was so bad I stopped driving my car. I searched on here for a fix but like most was told to go sra or there was no fix. I have diff bushing and 14mm bolts also. I brought my car to a buddy's shop we put it up on the lift. My hope was he could tell me if the clunk was from the trans or diff. He had me put on the parking break then let the clutch in/out quick to make it clunk. What he found was my diff was moving the rear diff mount bolt had backed out almost completely. We tightned it back up and guess what I have ZERO clunk. I would check to make sure everything is tight do what I did and have someone under the car to see if there is movement.
     
  13. CarolinaCobra

    CarolinaCobra New Member Established Member

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    Thanks for the reply! I need to go try this asap. I had the car up on jacks and was doing some work when I made the video and I did check most of the bushings but it's very possible that I missed this. I need to get under there and tighten everything to spec just to see if it changes. If it does, then I know its an IRS/ bushings problem not the driveline slack.
     
  14. keith89

    keith89 Well-Known Member Established Member

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    some of us are running aluminum diff mounts. Also, the diff case is not moving at all in the video. Just the driveshaft is moving.
     
  15. CarolinaCobra

    CarolinaCobra New Member Established Member

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    I realize and I'm not convinced the bushings are the problem, but if he says he has the same amount of slack and yet he doesn't have a clunk at all (or it's minimal) than the driveline slack may not be what is causing the issue.

    I personally think the "cobra clunk" is a number of different issues that owners are all calling the same thing. There's all sorts of owners that have all sorts of different mods that still have the problem and there's owners who don't have any mods and yet don't have the problem.

    At this point I'll try anything. Even just reducing the problem would be wonderful.
     
  16. ludbg

    ludbg New Member Established Member

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    but did it move like on the video or u just felt it while driving? cuz on the video hes moving it by hand and the differential isnt moving at all just the driveshaft
     
    Last edited: Mar 17, 2011
  17. BIGV

    BIGV GO BIG OR GO HOME!!! Established Member

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    Mine moved just like his by hand. Since the diff is so heavy I doubt it would move by hand. You could not tell mine was moving until under load. I am not saying this is your problem it could be something else of course. I can tell you that when mine clunked i could not only hear it but feel it. Hope this helps and I hope you figure it out I know it is annoying and ruins the driving experience in these cars.
     
  18. Fast GTO

    Fast GTO Member Established Member

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    I think the driveline play is normal and the clunk is caused by something else. I need to check my diff again when I put in the kmember. Unfortunately I don't think aluminum diff mounts will fit with my LPW cover.
     
  19. ludbg

    ludbg New Member Established Member

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    video of mine

    well today i got under my car to make a video and it does seem like to do exactly the same thing but I noticed that there isnt any PLAY in mine since if i turn the driveshaft even a little my half shafts turn! even if i do it slowly. but they move too much at the cv boot joint connection when it shouldnt it means the ujoint in there is bad??
    here are some quick videos that i made

    the wheels are locked and the halfshaft is moving where the joint is inside the cv boot
    that seems like too much play to me

    [nomedia="http://www.youtube.com/watch?v=YNJrHuR9GDY"]YouTube - 2[/nomedia]
    [nomedia="http://www.youtube.com/watch?v=PU3hKViQlYQ"]YouTube - halfshaft 1[/nomedia]
     
    Last edited: Mar 18, 2011
  20. pdm

    pdm Newbie Established Member

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    First of all, can you further explain the sound/feel of your "clunk"? Is it a rigid sound like two hammers hitting or is it softer like something hit the floor in the back of the car? For now, I'm going to assume it's the softer sound because I don't see enough slack in those videos to believe otherwise. I agree with Bob Kurgan (I have no idea who that is) I've worked on too many 4x4's with some seriously sloppy diffs and trannys that had no clunks but did make some nasty sounds at speed. If your R&P setup is way off or worn, you symptoms would be similar to what ludbg is experiencing.

    The clunk sound is not going to be caused by driveline slack alone, however, it is directly magnified by whatever slack (no matter how little) you do have. I'm not saying that it's not possible to have enough slack to cause a clunk, but that is certainly not you. If you have the stock diff mounts, that is where I would put my money.

    The cobra IRS is new to me, but it's not rocket science. From my experience diagnosing drivetrain and chassis pops and clunks, you have to have a serious problem before you can detect it with just using your hands. Like BIGV said, only way to tell is to get in the car and watch from below.

    Try this:
    1. Do some homework. Read the IRS tech article that's already been referenced and read over the info on fulltiltboogieracing.com.
    2. Make double sure EVERYTHING is tight.
    3. Set up your video camera under the car to record different areas (I would start with the rear diff mount, because I think that is your culprit.)
    4. Get in your car and do whatever it is that causes the clunk.
    5. Closely review the footage and try to detect any movement (you won't always be able to see it, but with as little driveline slack as you have, I'd say that you'll be able to.)
    6. Repeat with shots of different areas until you see something move.
    7. Post up the videos so you can have more eyes on it.

    Good Luck :thumbsup:
     
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