I've got some Issues... well not me, but my car!

General Discussion

  1. 74.Dodge.Dart.S

    74.Dodge.Dart.S Well-Known Member

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    Alright so I'm having some troubles with my 74 Dart Sport. The noise is from either the drive shaft, or the 7 1/4 rear end. I'm not sure exactly what it is yet, but I did record a 24 Second video of what is happening. Around the 15 second mark you will hear the clunking/slapping sound. This usually happens when turning or accelerating from a stop and goes away around 30-40mpg. I plan on opening up the diff, but I also tried shaking the front and rear of the drive shaft. The rear drive shaft feels solid, but there is a tiny amount of movement in the front u-joint. (I'm not sure what's acceptable) What am I missing here? Is my differential toast or do I have a bad u-joint?

     
  2. opus65

    opus65 Well-Known Member

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    Pull the rear cover.
     
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    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      I think you have multiple problems;
      A noisy pinion bearing, and maybe a loose pinion yoke
      a bent driveshaft,
      possibly out of balance wheels,
      and you engine idles like it is getting too much EGR,lol.
      IDK about the slapping,
      unless you don't have a SureGrip, then it could be that there is something wrong inside with the spiders and crosspin.
       
      Last edited: Oct 1, 2020
    • 69FBCuda

      69FBCuda Life in the Fast Lane FABO Gold Member

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      Should be able to isolate the noise
       
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      • 74.Dodge.Dart.S

        74.Dodge.Dart.S Well-Known Member

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        Thanks for the reply!
        Honest questions here, How would a drive shaft get bent? And also how do you adjust the EGR? Not sure If it matters, but this was from a cold start, no choke and I had to feather the gas so it wouldn't die until I put it in 3rd gear to let the clutch out. This noise started out of blue one day. I do think the axle bearings could be bad... I can also check to see if any weights came off from the tire too when I under there next...
         
      • SpeedThrills

        SpeedThrills FABO Gold Member FABO Gold Member

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        Before I listened , I was gonna say start with the easy stuff and check lug nuts. But that doesn't sound like loose lug nuts. Use a stethoscope. If you don't have one, hold one end of a wooden broom handle to different areas, the other end to your ear.
        You'll have to pull the driveshaft to inspect u joints. You'll feel "crunchiness" if one is bad. Replace both if one is needed. U joints should have no slop.
        I would thnk the only way to bend a driveshaft on a low powered, no slicks, street car would be to run over something.
         
        Last edited: Oct 1, 2020
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        • TrailBeast

          TrailBeast AKA Mopars4us on Youtube

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          I’d bet you the rear U joint is dry and eating itself.
          Note how the shaft goes off center and then straightens up when spun faster.
          Not feeling play in that U joint doesn’t mean it’s good.
          They can be tight because the grease is all gone and it’s binding.
           
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          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            Hyup, I'll go with @TrailBeast on the driveshaft thing, instead of bent. It helps explain the hop when it first starts to spin, which I wondered about, but it didn't connect inside my brain.
            The EGR remark was just a poke at the sound of the idle. which is a normal function of a performance cam at low rpm.
            But I'm sticking with a noisy pinion bearing.
            As to the flapping, I wouldn't want to place any bets on that; but I would hold off on the diff inspection until after the U-joint is looked at.
             
          • 74.Dodge.Dart.S

            74.Dodge.Dart.S Well-Known Member

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            Thanks for the helpful insight! I will pull the drive shaft and take a look! I know I didn't hit or run over anything. And from what I know its never had slicks. Its just the ol' 318 7 1/4 setup. I hope its just the u joints. Wouldn't be a bad fix if so!
             
          • 74.Dodge.Dart.S

            74.Dodge.Dart.S Well-Known Member

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            I do notice that! Out of the two, the rear u joint was tight but most dirty. almost like caked on grease.
             
          • 74.Dodge.Dart.S

            74.Dodge.Dart.S Well-Known Member

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            It does have a cam in it... I really wish I knew what was done to it. When I bought the car 6 years ago the guy said it had a cam and was .30 over. But he didn't have papers and couldn't remember anything else on it. It's due for another rebuild or upgraded to a 360 since its smokes a little and is leaking out of the main seal.
             
          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            YUP!!!

            !!!READ THIS CAREFULLY!!!! You can NOT "check" U joints by looking, by shaking, or by guessing. There is ONLY ONE WAY. That is to REMOVE the shaft. You remove the two rear caps and inspect, and you move the rear joint through it's movement, feeling for "dryness" and roughness in the needles

            You take the yoke in hand and move both sets of caps the same way. You will feel looseness, "over" tightness" caused by dry needles, and so on.............
             
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            • harrisonm

              harrisonm Well-Known Member

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              As usual, someone else beat me to it. I had almost the exact same thing several years ago. After throwing money at several other things, It wound up being the rear U-Joint. The U-Joints were fairly new, so it couldn't be that, right?
               
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              • oldkimmer

                oldkimmer FABO Gold Member FABO Gold Member

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                Put a mark on the shaft and pinion yoke so u can assemble it the same way it was. Kim
                 
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                • Mopar Tim

                  Mopar Tim FABO Gold Member FABO Gold Member

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                  And be very careful running the driveshaft while jacked up. Can be very dangerous......
                   
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                  • TrailBeast

                    TrailBeast AKA Mopars4us on Youtube

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                    Absolutely.
                    The yoke being reinstalled 180 from where it was can cause balance issues.
                     
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                    • 74.Dodge.Dart.S

                      74.Dodge.Dart.S Well-Known Member

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                      Ok so I pulled the drive shaft tonight and was able to inspect the U Joints. The caps fell off the rear U joint as I pulled it out. There is noticeable difference in the front and back. The front is a lot smoother with maybe some movement. (Hard to really feel any play in that one.) The back is "dry/tight" when moving it around. I mean its not hard to move around, but it doesn't move freely. I put the caps back on that fell off and made sure all the needles were still in place in them. Spinning the cap around it does sound rough! like a bad bearing. My next question is how do I know what to replace them with? On the drive shaft itself there's two different numbers on each end 2660724 and 2560724. On one U joint its has USA 108, and the other USA 300. Any help on how to look up replacement U Joints?
                       
                    • pt70

                      pt70 Well-Known Member

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                      Both u-joints should be the same. There are 2 sizes of u-joints. 2 1/8'' and 2 5/8''. Measure the inside dimension of the rear end yoke flanges. Yours should be the smaller one.
                       
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