Clunkin Sound
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HT4100 4.1, 4.5, 4.9 Discussion, Clunkin Sound in Cadillac Engine Technical Discussion; I got a problem... When coming from a stop (Red Light). I hear a Metallic Clunk on acceleration, And it ...
  1. #1
    hcaddy95's Avatar
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    Clunkin Sound

    I got a problem... When coming from a stop (Red Light). I hear a Metallic Clunk on acceleration, And it gets louder depending on how hard you get on the gas.

    I did look at things and didnt see anything out the ordinary except a motor mount on the front side of the motor by the radiator that was full of what looked like grease tighten all body to sub-frame mounts and all other mounts look good. kinda stumped

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    HUF
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    Re: Clunkin Sound

    Quote Originally Posted by hcaddy95 View Post
    I got a problem... When coming from a stop (Red Light). I hear a Metallic Clunk on acceleration, And it gets louder depending on how hard you get on the gas.

    I did look at things and didnt see anything out the ordinary except a motor mount on the front side of the motor by the radiator that was full of what looked like grease tighten all body to sub-frame mounts and all other mounts look good. kinda stumped
    That dog bone (torque mount) is easy and cheap to replace. Open the hood, powerbrake and watch from the driver seat the movement of the engine.

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    Re: Clunkin Sound

    Make sure ignition timing, engine temperature, and fuel octane are in spec. 10 deg BTDC, 190-210degrees, 91+octane respectively.

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    Re: Clunkin Sound

    No its not a driveability problem and the Dog bone motor mount is fine, Im thinking its the mount thats on the front of the motor down by the radiator any pointers on getting to the top of that mount . It almost sounds like the exhaust is poping like the motor is moving to much. And the 4.9 gets super premium and the timing is set at 12 BTC, the engine runs very quite i mean very quite surprised how quite it runs for a pushrod motor/w 107k

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    Re: Clunkin Sound

    I would try backing the timing off to 8 deg (or even 6) to rule out an engine knock/spark knock problem. Engine knock can have a very convincing metal rattling sound. If it's not a knock issue, diagnosing it over the internet can be next to impossible. Maybe have a friend brake-torque it while the hood is up and see where the sound is coming from...

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    Re: Clunkin Sound

    Just seeing if any deville owners had similar problems in the past, Ill fix it soon

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    Re: Clunkin Sound

    It could be the CV joints.

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    Re: Clunkin Sound

    Quote Originally Posted by hcaddy95 View Post
    I got a problem... When coming from a stop (Red Light). I hear a Metallic Clunk on acceleration, And it gets louder depending on how hard you get on the gas.

    I did look at things and didnt see anything out the ordinary except a motor mount on the front side of the motor by the radiator that was full of what looked like grease tighten all body to sub-frame mounts and all other mounts look good. kinda stumped
    You are probably on the right track with the motor mount, unless that is you are confusing a clunk with pinging/knocking like suggested.

    In '94-'95 a hydraulic-type mount was used in the position you described. It's liquid filled. The greasy mount could be a mount that has leaked, which could very well be causing your clunk. First be sure the "grease" didn't come from elsewhere, above the mount dripping down. If you know the mount has leaked, replace it as you know it's bad anyway. Then move on if the clunk still exists.

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    Re: Clunkin Sound

    Well its clunkin more now repeatedly Clunk Clunk right after each other,and its gotten louder.

    But when I did look at things a few weeks ago I noticed it stoped for awhile then returned.

    All the literature Iv'e been reading is telling me to replace axles Im going to do them this weekend

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    Re: Clunkin Sound

    Axles are usually good for the life of the vehicle. They are a low maintenance item. Really the only thing that can go wrong is bad CV joints. Contrary to popular belief, these are actually quite reliable as they are in a sealed environment, always submerged in grease. Problems start when the grease is removed or contaminated with dirt and/or water.

    Are the rubber CV joint boots leaking? is there grease slung around in the wheelwell? Rotate the axle with your hands and see if you can feel slop in the joints. If not, the axles are good.

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    justin4yu is offline Cadillac Owners Member
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    Re: Clunkin Sound

    I have seen flexplates crack at the crankshaft bolt holes outward to the torque converter bolt holes, and cause a clunk that get louder over time.

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    Re: Clunkin Sound

    Yeah I put new drive axles on the car and didnt fix it I guess i should have listened to drew Ive noticed it does it to when the transmission shifting. I guess i should have replaced that leaking motor mount.

    But im seeing two differant kind of motor mounts at the part store. one's solid and one's liquid filled. which one would be better?

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    Re: Clunkin Sound

    Aftermarket manufacturers released a solid mount to address the common problem with the hydraulic mounts.

    If you want to keep it as Cadillac had it, you know what to do. If you want peace of mind that this won't happen again, the solid mount will increase your chances.

    I'm not sure of the solid mount's performance as I've never tried one. I'm going to assume that it doesn't isolate vibration as well as the hydraulic, but I doubt it would really be that noticeable.

    Usually when that forward mount fails, the torque strut (dog bone) soon follows since it's doing a lot more work with the decrease in support. (this is the case, at least, in my experience with GM W-bodies) They usually end up having to be replaced in pairs, especially when it's gotten to the point of a serious clunk. You might want to make sure that the torque strut looks good as well. If not, they are really cheap.

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    Re: Clunkin Sound

    Ugh, my 1992 is doing the same thing and its driving me crazy! I get a clunking sound everytime I go from a standstill at a red light. Its a very pronounced "clunk" that almost sounds like its coming from the rear. Ive thought it was related to the exhaust, but I had all of that done. So Im totALly baffled as to what is causing it. When you find out, please let me know. It may be the same issue, since we have the same motor.

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    Re: Clunkin Sound

    Quote Originally Posted by caddydave2001 View Post
    Ugh, my 1992 is doing the same thing and its driving me crazy! I get a clunking sound everytime I go from a standstill at a red light. Its a very pronounced "clunk" that almost sounds like its coming from the rear. Ive thought it was related to the exhaust, but I had all of that done. So Im totALly baffled as to what is causing it. When you find out, please let me know. It may be the same issue, since we have the same motor.
    Put it on lift and have someone powerbraking while you are watching for the source of the sound under the car. That's how I found what was driving me nuts for years in two seconds. It was a bracket running over exhaust pipe. It seemed to have enough clearance, but when the the engine and the exhaust system moved under acceleration, the whole thing moved back enough to touch that bracket. Pried it off a little bit and the clunk was gone for ever.

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