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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. pdm

    pdm Newbie Established Member

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    ANY play in a cv or u-joint is too much. You, my friend, need new cv axles.
     
  2. ludbg

    ludbg New Member Established Member

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    ye but shouldnt my car be making clunking noises when turning too? because it isnt ...
    also i was told that my irs is a 2001 which would mean 31 splines but the guy said he wasnt sure it might be a 99 with 28 splines
    how can i tell??
     
  3. pdm

    pdm Newbie Established Member

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    Sorry to muddy up the OP's thread with this discussion, but hopefully it will add some useful information.

    No. Like I said, driveline slack in and of itself is not going to create a clunk. Also, any clunk is caused when two objects collide. Once the vehicle is in motion, everything is in full contact. The only time that changes is when you go from acceleration to deceleration. How do you figure that turning would cause any change in the cv shaft? A clunk when you turn is a good indicator of something wrong in the knuckle or hub.

    The cobra IRS is new to me, so I don't know any visual nuances that would set the two shafts apart. If you can, compare it with a verified 28 spline and 31 spline. Otherwise, just count the splines.
     
  4. CarolinaCobra

    CarolinaCobra New Member Established Member

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    Mine seems to be a pretty heavy sounding thud and I definitely feel the car shaking. I can make it "clunk" when shifting gears, when letting off the gas or getting back on it, and from a standing start slipping the clutch. I can handle the clunk when shifting because it's possible to "drive around it" so it's not really noticeable. My real complaints come from the other two situations.

    While driving, if I take my foot off the throttle and then get back on it, it will clunk. This is most apparent in low RPM situations (parking lots in 1st or 2nd, or cruising in 5th or 6th), or taking off in first if I don't rev it enough and slip the clutch a bunch. There just feels like a ton of slack. This is why I initially didn't think it was the bushings at all. But it does make sense now how they might not be the exact problem but they really just compound the issue.

    I'm going to tighten everything up and take a good, long look at the rear diff bushing and report back.

    No worries about clogging up the thread. This is all good info.
     
  5. ludbg

    ludbg New Member Established Member

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    mine is exactly the same and it is as PDM described the sound as "softer like something hit the floor in the back of the car"
    try to see if there is movement in the dif mounts using a crowbar or something. i would try it if i had jack-stands i dont trust the jack alone
     
  6. Jimmysidecarr

    Jimmysidecarr Semi user friendly Established Member

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    I do not believe the "Cobra Clunk" can be completely eliminated.
    It can however, without a doubt be greatly reduced.


    You can do that, I would like to see you post back up though because I have been running Royal Purple Max gear 75W140 since 07 and my clunk is NO LOUDER than the first day I drove the car with the TrueTrac in it. Did you drill and tap a drain plug in it yet? I did. Without it fluid changes are a royal PITA!
    Ford speced FULL syth lube because the diff only holds about a quart and a half and it runs hotter than HELL. The FULL Synth lube is to keep your ring and pinion from burning up with only that tiny bit of lube. TrueTracs can run Full synth if the original app speced it. The bias ratio I believe is slightly reduced when running Synthetic over Organic, which makes sense if you think about it, less friction = less bias, but also longer gear life.
    I won't be running organic in mine.


    It is normal.

    It's not TrueTrac wear..... my 4 year old TrueTrac has the exact same clunk it did when new.
    It's not the TrueTrac.


    The loose, soft, cooked, worn out, made of low NVH silly putty, OE bushings make it worse, they also contribute to wheel hop.
    When brand new without as much play, they dampened the clunk a little, but they never did completely eliminate it
    My 04 had the clunk brand new off the lot.


    CVs that clunk on turns are front wheel drive, it's OK whoever told you that just thought they were helping.
    When you are driving axles that have to steer the CV joints will turn with the spindle while rotating, making the balls in them roll in a non-worn area of the joint, when they transition through, they click... repeatedly.


    You need to post more often!:rockon:
    Thank you for your contribution today.:beer:

    I have the complete FTBR bushing kit. I installed it myself. When I did I took my diff chunk(center housing) to work and had a tech friend install my True Trac and re-set my ring and pinion. I asked him to set it up as tight as he felt would still be OK.(The very end of the tight side of the spec)

    Cars will be a little different but mostly driver perception is what will be different and in the case of the "COBRA CLUNK, it can be by a HUGE AMOUNT!

    You can GREATLY reduce the cobra clunk but I would not advise spending any money at all if you think you are going to completely eliminate it.

    Is the FULL bushing kit worth doing? ABSOLUTELY!!! Every IRS Cobra should have this done!

    Just know going in that there are many factors combining together to create this clunk, and by doing the bushings you will also be correcting many other IRS issues that are significant and EXTREMELY detrimental.
     
  7. pdm

    pdm Newbie Established Member

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    A pry bar of some sort on a suspected area works well as a testing tool, but, yes, be careful not to pull the car down on yourself.

    You got that backwards, If you had enough driveline play to make that kind of noise, you would have serious issues. What you describe sounds just like a mount moving around somewhere, and it doesn't necessarily have to be in the rearend. Sounds almost like a tranny mount to me.

    The reason your clutch/throttle work has so much effect on the sound is this: The engine induces torque into the driveline and the clutch/throttle obviously control how much. The internal components (gears, driveshaft, etc.) transfer the torque through the drivetrain and, ultimately, to the wheel/tire. All the mounts, from the motor to the subframe, work together to contain this torque and hold the drivetrain and unibody together as one solid unit. Now, the cobra clunk occurs when a component in the drivetrain (that is supposed to be stationary) moves and makes contact with another component or the unibody. This can be at any defective mount or bushing, but will not be caused by normal (or even excessive) operating movement in the driveline. Think of it like this. If someone crawls under you car and smacks the diff or tranny with a hammer, you can hear it but but there's not much to it. That would be similar to the driveline taking up slack. Now, if someone hits the floor pan with a hammer, it sounds like something came apart. That's pretty much the same as a mount flopping around. Internal components in the drivetrain will not transfer a significant sound (other than NVH) through the unibody unless something in broken.

    Case in point: On one of my Jeeps, I had an isolator go bad on a cross member, and under high torque, the transfer case would smack the tunnel. I watched while a friend loaded the drivetrain by powerbraking. I saw the isolator separate and the engine/tranny/tcase torque up enough for the output side of the tcase touch the bottom of the body. It was a quick diagnosis, but all the visual inspection in the world would not have shown anything like that. I've also seen similar situations when rubber motor mounts fail. It sounds like the whole front end is going to fall out from under the car.

    I know this is lengthy, and pretty much obvious, but there are pages and pages of comments on this site where people are speculating about what causes the cobra clunk. Maybe this painted a clearer picture to analyze what is actually happening.

    BTW, I've got the clunk bad! I have a theory, and I'll post pictures of the culprit after I rebuild the diff and IRS. There will be a build thread coming up in a couple of weeks.

    EDIT: Jimmy, you're welcome, and my rebuild will include the full FTBR set. I agree about eliminating the clunk entirely. I've seen a similar problem before with a truck. It's not an inherent problem with the drivetrain internals. I believe it just happens to be the resonant characteristics of the subframe and, mostly, unibody. I am going to try something on my car that will eliminate the resonance in the sheet metal, and I have a feeling that it will kill the clunk. Think of it as pressing your hand on a drum. When you strike it, there is no resonance. I have a feeling that the clunk is a similar phenomenon.
     
    Last edited: Mar 18, 2011
  8. Blueline

    Blueline Active Member Established Member

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    This thread is def. interesting. Pdm great posts you covered alot of very key points. I just finished rebuilding my rear, new diff. new ring pinion, bearings etc.... I set the backlash at .007" carrier preload, pinion pre-load etc. was all perfect in tight end of spec. I went over the entire rear of the car. Before I took it apart due to my blown rear this thing would clunk and sound like it was gonna fall out of the car. Now 350 miles later... not one sound! I get zero clunk, zero play in the rear etc. The car feels like a brand new car. You feel nothing when I shift and let the clutch out or engage the clutch etc. I think theres def. a solution to the mysterious clunk, at least to minimize it as Jimmy stated.
     
    Last edited: Mar 18, 2011
  9. CarolinaCobra

    CarolinaCobra New Member Established Member

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    pdm and Jimmy thank you very much for the replies! All the knowledge in this thread has been very helpful. I'm hoping to do some work this weekend so I'll update as I go.
     
  10. ludbg

    ludbg New Member Established Member

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    ok, hijacking again... yesterday I replaced my differential bushings and found out i already had 14mm bolts installed and the Clunk (bang) is still there and my differential whine has gone louder... i had my friend turn the drive shaft from underneath the car while i was in the car and the noise is there when he moves it and im 100% sure its the differential so what now?
    could my pinion nut be loose? pinion gear is worn too much?
     
  11. CarolinaCobra

    CarolinaCobra New Member Established Member

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    Well that sucks. This is what's keeping me from doing the solid diff bushings right now. I want to be certain they are the problem. There are owners that have/have had this problem with solid bushings installed. My car is daily driven too and the diff noise would bother me.

    I've been under the car recently dealing with a cv joint boot tear and replacement of the half shaft, and I haven't seen anything out of the ordinary. The bushings all look good. I know I've read that some owners have had poly bushings that "looked" fine from the outside but really were trash once they pulled the subframe out. But I just can't seem to get any substantial deflection with a pry bar or anything. All the bolts are nice and tight too.

    ludbg, please update if you figure something else out.
     
  12. mmustangsrus

    mmustangsrus boost makes daddy happy Established Member

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    if you want to get rid of the "irs clunk"

    The Finest IRS Delrin Bushing Kit


    go here ^^^ & get you some 9/16" grade 8 front sub-frame bolts and grade 8 nyloc nuts
    & the m.m. low profile irs 14 mm bolts



    [​IMG]

    i did the complete FTBR kit & those bolts no more clunk !!! :banana:
     
  13. ludbg

    ludbg New Member Established Member

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    The noise my car makes is more than a clunk, i call it a bang. it sounds like someone took a rubber sludge hammer and hits my frame. its that loud. It even sounds that loud when my friend twists the drive-shaft with bare hands. i have the 14mm bolts and there is 0 movement in the bolts and diff. bushings.
     
  14. arc00ta

    arc00ta Member Established Member

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    Mine does the same thing. I installed the FTBR aluminum bushings and subframe bolts, no change. My transmission is built as well. Its really annoying, I can hear the slack "spool up" and let back out when I get on and off the gas or use the clutch. I can make it sound like someone is beating the bottom of the car with a rubber mallet just by tapping the gas lightly.

    As an experiment, I have tried different pinion angles and found the least slack is with +3 on the diff, where my driveshaft actually goes up from the transmission and it quieted down a lot. I wasn't sure how that would effect anything so I put it back though.
     
  15. ludbg

    ludbg New Member Established Member

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    here is a vid i found on youtube of some e46. the noise my car makes is identical loud bangs

    [nomedia="http://www.youtube.com/watch?v=OhsDaSA0ZFk"]YouTube - E46 excessive differential play.avi[/nomedia]
     
  16. unforgiven

    unforgiven Humble Established Member

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    Ok, I'm in. My Cobra has play in the driveshaft as shown in the OP's original video. I am the second owner of this Cobra so I ordered the FTBR differential bushings to help with the "clunk".

    Well, the previous owner did the entire bushing kit (I had no idea) but the car clunks as described by other owners. It is frustrating and I fear that I am harming the car. I am subscribing to this thread.
     
  17. TRQJUNKIE

    TRQJUNKIE Justa Slobra Established Member

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    Mine does not have even half that amount of play. My guess is ur rear has too much backlash. If you go to do the diff bushings take the diff housing to a mustang shop near you, or someone who knows wat they r doing, and let them check everything inside over. Can't hurt... That is way too much play I don't care who u r.

    It sounds like the pinion gains speed over the ring gear and when the pinion hits the ring gear it is making that "clunk" sound. That's my theory.
     
    Last edited: Apr 4, 2011
  18. ludbg

    ludbg New Member Established Member

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    Here is an update from me :)
    I really don't want to deal with differentials and shops want 350 just for labor for opening it up and rebuilding it so i just bought (25 mins ago) a complete rear-end of a 99 with 85k miles and it has 0 play just the minimal backlash. I'm so happy!!!!:banana::banana: will be putting it in next weekend. then ill disassemble my old one and see whats up in that mofo. :shrug:
     
  19. nooner

    nooner New Member Established Member

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    That shouldn't be a problem. I have FTBR aluminum diff bushings installed with the LPW diff cover on my car. I had a shop do the installs of both at the same time along with 3.73 gears.
     
  20. BIGV

    BIGV GO BIG OR GO HOME!!! Established Member

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    You do know the 99 is different from the 03/04 irs right.
     
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