is the clunk drivetrain backlash?
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  • 2 Post By Robert Newman
2004-2007 Cadillac CTS-V General Discussion Discussion, is the clunk drivetrain backlash? in Cadillac CTS-V Series Forum - 2004 - 2007; Guys, On my V when I am in first and moving (at about 5-10 mph) and I put in the ...
  1. #1
    ctsvett's Avatar
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    is the clunk drivetrain backlash?

    Guys,
    On my V when I am in first and moving (at about 5-10 mph) and I put in the clutch, I get a clunk from the drivetrain. Is this backlash or do I need to take the car in?
    I know others have reported a clunk, is this the same?

    Other than this annoinace, the car is AWESOME...

    Thanks,

    Reed

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  3. #2
    MotorMouth is offline Cadillac Owners Member
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    Re: is the clunk drivetrain backlash?

    I get that as well........... If I am faster than that no backlash. I had a 94 camaro with a 6 speed that did that too. No other drivetrain or gearing issues, noises, etc.

  4. #3
    Robert Newman is offline Cadillac Owners Member
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    Exclamation Re: is the clunk drivetrain backlash?

    I have done quite a bit of work on the clunk issue since I have the problem on my CTS-V. The problem comes from the soft rubber torque coupling and the drive shaft center bearing mount. Both of these parts are made with rubber that is very soft to reduce road and gear noise inside the car. The clunk occurs when the clutch is suddenly released when there is torque on the drive shaft. The large amount of torque created on the dirve shaft in low, second, and reverse twists these rubber components like a rubber band. When you push in the clutch quickly this torque is suddenly released and the rubber parts quickly unwind. GM calls this torque reversal, but it is not actually a reversal. The clunk noise actually is not made by the drive shaft. The clunk comes from the ring and pinion gear in the differential box. When the drive shaft unwinds suddenly the pinion teeth impact the ring gear teeth and you hear the noise. The noise is loudest if you stand outside near the rear wheels. The noise is comming through the axles and into the wheels, but it is all caused by the soft rubber in the drive shaft. Some of this sudden unwinding is caused by the drive shaft itself since it appears to made from aluminum. Aluminum has one third the stiffness of steel so this causes some of the problem, but I think 90% of the problem is from the rubber. I have had emails on this subject going through the Southeastern Cadillac service rep to power train engineers at GM. Here is their response:

    "The CTS-V driveline has a few "normal" operating characteristics that some customers may find objectionable. Obviously this is because the driveline was designed with high speed performance and durability as the primary criteria, pleasability issues that normally rank as high Cadillac priorities were relegated lower because this car is not like other Cadillac's. We know torque reversal in the driveline will cause an audible clunk and this can occur under various common driving/clutching conditions."

    "Torque reversal is a result of normal axle backlash, the driveshaft rubber isolation flanges, the center support and the dual-mass flywheel working together. This phenomenon has been thoroughly evaluated by engineering and has been validated as not detrimental to durability or high performance usage. It is normal and no repairs should be attempted."

    They will not give me the e mail address or the phone number of the engineer. Please send an e mail to: (email address removed at Robert Newman's request) and complain about this problem. Mike is the service manager for the Southeast and he will forward your comments.

    You can create the clunk without moving the car. Put the parking brake on. Shift to first gear. With the engine at idle (about 1000 RPM) slowly let the clutch out until the engine bogs down to about 600 RPM. The very suddenly push in the clutch and you will hear about three clunks. Do not give the engine any gas when you are doing this. Just idle speed is good enough.

    I actually blocked the car up very safely and got under the car. I trained my wife to go through this procedure while I was under the car, and I could see the drive shaft clunking back and forth.

    In my younger days I was a power train engineer for off highway equipment so I know something about this issue. To me it is an unacceptable defect in the design of the CTS-V. So far Cadillac will not try to correct the problem. If you complain it will help. They tell me I am the only one complaining. The solution is to make these rubber parts from higher durometer (stiffer) rubber.

    Please give me a call and I can tell you even more about trying to relsove this issue. My daytime phone numbers are 803-822-7400 or 803-429-7000.
    flyhi152 and flyhi152 like this.

  5. #4
    Rob Ketcham is offline Cadillac Owners Member
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    Re: is the clunk drivetrain backlash?

    Your explaination of the driveline noise is knowledgable and seems accurate, and I agree that a Cadillac shouldn't have this design flaw. My 98 LS1 SS Camero with a 6 speed did not have it. I thought for a while it was me. I have always driven "do it yourselfers" but even my old FJ60 doesn't have what feels like this much slack in the differential.
    I have found that when I depress the clutch, slowly, and do not back off the throttle, and indeed do not take the clutch all the way to the floor (perhaps it is a dual plate?) I can minimize the clunking. But even with all my efforts, sometime it is just wound up enough that the energy does release itself as a "clunk".
    Are you thinking that substituting poly for the rubber would eliminate the problem, I'd be interested in your thoughts.
    I am on the Eastern Shore of MD. Would you still suggest contacting the southeastern service rep, or should the pain get spread around a bit?
    Rob Ketcham

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    ctsvett's Avatar
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    Re: is the clunk drivetrain backlash?

    Thanks for the awesome explanation. I will bring my car in and complain as well as call the number you posted.

    Reed

  7. #6
    Cal
    Cal is offline Cadillac Owners Enthusiast
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    Re: is the clunk drivetrain backlash?

    I understand you don't like hearing the noise, but is there a risk to the car itself from this, or is it just sloppy engineering?

  8. #7
    globed70 is offline Cadillac Owners Enthusiast
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    Re: is the clunk drivetrain backlash?

    I got used to it for 18k miles in my (former) 97 Viper GTS, that it doesn't really bother me. At first, I thought it was related to the T56 (since this is shared between the cars)... but it sounds like you've identified another cause (that must be common between the cars). Although I won't complain, I wish you luck and look forward to understanding why the V (and the Viper) were designed with this "feature."

  9. #8
    urbanski is offline Cadillac Owners 10000+ Posts
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    Re: is the clunk drivetrain backlash?

    Quote Originally Posted by Robert Newman
    I actually blocked the car up very safely and got under the car. I trained my wife to go through this procedure while I was under the car, and I could see the drive shaft clunking back and forth.
    .
    holy crap, i cannot believe anyone would do that

  10. #9
    lasstss's Avatar
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    Re: is the clunk drivetrain backlash?

    Different things to different people on this one. Its a very minor annoyance. The description is correct. If you are giving the V a blip up to a light and 'unload' you get some chatter. I dont know if its the diff, my impression is its gear chatter in the trans from the unwind. Same problem the Vetts had at idle until they went to the dual mass flywheel that we have in the V. This was due to pulse loading caused by the engine.
    Just keep im mind that Caddy wants keep the V somewhat sedate. I have converted quite a few of my cars to urethane all around. It tightens everything up alright. Also keeps the dentist in business putting your fillings back in. Also increases road noise substantially. IMO....

  11. #10
    Robert Newman is offline Cadillac Owners Member
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    Re: is the clunk drivetrain backlash?

    To Rob Ketchem from Robert Newman:

    I think using urethane to replace the rubber may solve the problem, but this is not a change that would be easy to make. This would be a change that GM would have to make, and it would probably be easier to simply use a higher durometer rubber. In my judgement most of the wind up is a result of the very soft rubber that mounts the drive shaft center bearing to the car uni-body. This is really not wind up at this point. The drive shaft probably compresses this rubber to one direction or the other and when the clutch is released quickly it releases its stored up energy. The rubber is so soft at this mount that you can put your hand on the drive shaft at this bearing and push or pull and then you can see and feel the drive shaft deflect. It is just too soft.

    The noise comes from the pinion hitting the ring gear, and this impact load is probably not large enough to cause damage to the gear teeth surfaces, but I am not sure about this. The gear tooth contact loads are probably much higher when you open up the throttle in low gear.

    I have a WS6 Firebird with the old 350 and six speed. It has a steel drive shaft with old style universal joints. This drive shaft design is very stiff and I cannot make it create the clunk.

    Give me a call tomorrow at 803-822-7400 or 803-429-7000, and I will tell you some more.

    Best regards,

    Robert Newman

  12. #11
    6104696 is offline Cadillac Owners Connoisseur
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    Re: is the clunk drivetrain backlash?

    I have driven 5 CTS-V's; they ALL had the clunk.....(inluding the one I finally bought)....

    I have driven one Z06; it did not have the clunk.

    Doug

  13. #12
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    Re: is the clunk drivetrain backlash?

    Quote Originally Posted by 6104696
    I have driven 5 CTS-V's; they ALL had the clunk.....(inluding the one I finally bought)....

    I have driven one Z06; it did not have the clunk.

    Doug
    The Z06 doesn't have any driveline per say - so it can't have driveline backlash. The gearbox (trans) is mounted in the rear and so the conventional driveline doesn't exist.

  14. #13
    ssmith100 is offline Cadillac Owners Connoisseur
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    Re: is the clunk drivetrain backlash?

    Damn Benjet, you beat me to it. (ZO6 drivetrain) I had a 2000 Ram Air Trans Am (LS1 6-speed) that clunked just like my V does. I think a lot of people who have these cars are going to have to decide whether they want a luxury sport car or a not so luxury race car. I personally think the wheel hop problem is a bigger issue than the backlash problem. But with a 50,000 mile powertrain warranty, they (cadillac) can just keep replacing parts when and if I break them.


    Shane

  15. #14
    6104696 is offline Cadillac Owners Connoisseur
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    Re: is the clunk drivetrain backlash?

    unless there is some sort of magnetic (or magic?) coupling between the front-mounted engine and the rear mounted transaxle, then there is a driveline. However, my point was that there IS a difference between the two, and in the difference lies the clunk.....So I believe that Robert's analysis is a correct one.

    cheers.....

    dhg

  16. #15
    Rich H's Avatar
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    Re: is the clunk drivetrain backlash?

    Seems like a quick fix would be to eliminate the rubber components and install a solid driveshaft as suggested by BMR. They also say it helps eliminate wheel hop. See attached link:
    http://www.ls1tech.com/forums/showth...07#post1420107

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