Drive train vibration. Scratching my head.

Transmission and Drivetrain Tech

  1. JoePole1

    JoePole1 A dude in a B body FABO Gold Member

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    Hey Guys. Could use some help here. Drivetrain is LA 360/904/8.25. Combo has been in the car for over 10 years. About a year and a half ago I developed a vibration at about 55 and by 70 it is pretty heavy. It is only under power meaning if I take my foot off of the accelerator it stops. It is also not constant. It sounds like waaawaaawaaawaaa. This all seemed to begin with a gear and sure grip change from 2.76 to 3.55. I tried turning the driveshaft orientation even though I marked it. No change. Thinking it must be from the rebuild (new gears, bearings and crush sleeve eliminator) we went back in and checked the contact pattern again and it looked great. The only thing I noticed is that the pinion preload was at 14 inch pounds with a spec of around 30 but when we tried to adjust, we could not increase it and we were applying over 200 ft/lbs. After putting in fresh fluid with additive the vibration felt like it came in higher around 65mph. I can also feel the vibration seat of pants at 30+ but not pronounced.
    I then started using 2 hose clamps and moving around the back end of the driveshaft in 90 degree increments to see if maybe it was out of balance. Vibration maybe changed a little but hard to tell.
    At this point I am not convinced it is from the rear end but it was the only thing I changed.
    I am not a drivetrain expert. I did the rebuild with a mechanic buddy of mine who has done quite a few similar rebuilds on GM's. He has not felt anything like this before.
    Any help is appreciated.
     
  2. krazykuda

    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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    Maybe the outer ring on the vibration damper spun on you....
     
  3. JoePole1

    JoePole1 A dude in a B body FABO Gold Member

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    I never marked it. Any way to check in car? Timing off? Engine runs great.
     
  4. krazykuda

    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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    Use a piston dead stop tool and put the #1 cylinder at TDC, then check where the TDC mark on the outer ring of the damper is.....
     
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    • JoePole1

      JoePole1 A dude in a B body FABO Gold Member

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      Thanks KK. Gotta order one. SBM is 14mm....correct?
       
    • Dana67Dart

      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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      It could be that by changing the engine RPM at a particular speed (diff gear ratio) you are noticing things that have been there all along but you didn't get to that engine rpm often enough to notice it? ( At 55 it is only about a 600 rpm diff????)

      Dies it do it with trans in neutral coasting but keeping the engine at the same RPM that was needed to go 55?
       
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      • JoePole1

        JoePole1 A dude in a B body FABO Gold Member

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        I don't think so but will try that.
         
      • Dana67Dart

        Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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        My thinking...
        1. If the engine at the same RPM creates the same vibration sitting still in the driveway it is engine / trans.
        2. If it happens while coasting in neutral, engine ideling but still moving at 55 to 70 it is drive shaft, rear end related, or tires / wheels.
        3. Both could be trans to some extent.
        What I posted earlier was meant to be the above.
         
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        • Murray

          Murray FABO Gold Member FABO Gold Member

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          How old are the axle bearings? Cupped tires, try rotating them.
           
        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          Does it vibrate in park or neutral? If so, you just eliminated the drive train.
           
        • JoePole1

          JoePole1 A dude in a B body FABO Gold Member

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          It does not vibrate in park or neutral so yeah I do believe it's in the drivetrain. What about the new gear or new suregrip? Could they throw out of balance somehow?
           
        • JoePole1

          JoePole1 A dude in a B body FABO Gold Member

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          Tires are good. Wheel bearings are old and definitely not eliminated from suspect but no side play and rotate smoothly. On the list to check.
           
        • JoePole1

          JoePole1 A dude in a B body FABO Gold Member

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          I think a couple of big clues are the vibration occurs at different speeds although I may not be feeling it so much at lower but it definitely gets pretty extreme from 60+ mph. Other thing is the tone. It's not steady. Kind of oscillates if that makes sense. WaaaWaaaWaaaWaaaWaaa...........
           
        • jimjimjimmy

          jimjimjimmy lobsterman FABO Gold Member

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          i had the same problem and it took a few days to figure but it turned out to be a crack in the race of the rear wheel bearing . i put new races and bearings in both sides and it now runs nice .
           
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          • KosmicKuda

            KosmicKuda FABO Gold Member FABO Gold Member

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            I made one by gutting an old spark plug.
            Ran a 3/8-16 tap through the body.
            Rounded the end of a 3/8 bolt to contact the piston.

            You might try driving the car in 2nd gear and bringing it up to the same rpm you see in 3rd at 60 mph. If the vibe happens I'd suspect the engine/trans. If no vibe then something in drivetrain after the trans.
             
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            • oldkimmer

              oldkimmer FABO Gold Member FABO Gold Member

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              If ur feeling it the seat then it’s in the rear. Drive shaft, pumpkin, axles or bearings or a bent housing. If u only got the torque on the pinion nut to 200 lbs after the fact then u already were asking for a problem. Kim.
               
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              • Divenut

                Divenut Well-Known Member

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                Pinion nut loose?

                Edit: oops..just saw oldKim's comment. Lol
                 
              • JoePole1

                JoePole1 A dude in a B body FABO Gold Member

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                The pinion nut was not tightened more when checking after rebuild/vibration. The rotating torque was at 15 inch pounds so still under spec. Odd. Not sure if crush sleeve eliminator played into that.
                 
              • Dodge72

                Dodge72 Odd one out

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                Holy crap! I literally came on here to post about dang near the exact problem. Above 65 mph is when it starts to get that low frequency vibration and "whoomp, whoomp, whoomp". 65+mph the vibration starts is higher (the oscillation gets faster) and the vibration gets a bit worse. Happened with my slant six /904/8.25, now it happens with my 360/904/8.25. Common denominator is the 8.25. Before we go in with a dial indicator, we pulled the inspection cover off and found the spider gears with wear and they move in an up and down fashion. My ring and pinion look fine. No shards of metal. Do your spider gears do the same? I have a video of it below.




                Apologies I'm not trying to hijack your thread. I'm hoping I can provide anything you may not have looked at and vice versa.
                 
              • JoePole1

                JoePole1 A dude in a B body FABO Gold Member

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                I am going to dig a little deeper over the next 2 days using the recommendations I got from members here (thanks). I'll check spider gear play when I pull the cover as my sure grip unit is new. Can't comment if that is normal or not. Will report back here. No worries about the Hi-jack. Misery loves company.
                 
              • krazykuda

                krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                • 512Stroker

                  512Stroker We are all here because we are not all there.

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                  You did not say who's gear set you used.
                  After market gears are not like they used to be, some are noisier than others.
                  Point is good luck finding a current after market gear set that does not make some kind of weird noise. Even with a perfect pattern.
                   
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                  • RustyRatRod

                    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    I wouldn't think so.
                     
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                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                      Have you checked the transmission mount to make sure it hasn't collapsed?
                       
                    • JoePole1

                      JoePole1 A dude in a B body FABO Gold Member

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                      I believe it's Motive gear set. No gear noise. It's the vibration that is causing the noise and only at high speed/RPM. Very faint at low speed (35).
                       
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