Does 3 in lbs matter?

Discussion in 'Transmission & Driveline Topics' started by LT1 WS6, Aug 12, 2016.

  1. LT1 WS6

    LT1 WS6 Veteran Member

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    I'm fighting a vibration issue that comes in right about 60 mph. Without going into all the troubleshooting I've been through, let's just say it's in the driveshaft and pinion gear area. I've adjusted pinion angles repeatedly with no change in the vibration and changing the rear u joint hasn't helped either. Driveshaft is balanced properly, too. It's nothing obvious unless I've missed something but I'm confident I haven't.

    What I'm wondering about is a noise I hear and feel in the pinion. When I have the car in first gear, at idle, and with the rear wheels off the ground, the rear end is quiet. Do the same thing in 4th and I start to hear a noise and can feel some vibrations coming from the front snout of the diff. Vibrations may be a poor choice of words but I can feel that there's obviously something rotating in there. Which of course there is. I'm curious to know if this is normal? I've never been under a car paying attention to the rear end like this before.

    When I built the rear end, everything set up properly but I over torqued the nut and crushed the sleeve a tad too much. By my readings, I had about 3-4 in lbs too much drag on the pinion bearing. Could this be what's causing the vibration issue I'm feeling at 60mph? It's definitely speed related and the car runs smoothly until 60.

    I've put a few hundred miles on the rear and it's dead quite. Drained the gear oil recently and there are no metal shavings or anything abnormal in the oil. There's absolutely no incorrect play in the pinion. Unfortunately, I did other work at the same time as I did the rear end so I can't say for certain this is the culprit. I'm just not sure if the over tightening matters that much.

    Thoughts?

    Thanks
     
  2. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    Sounds more like a drive shaft issue. Have you tried flipping the drive shaft 180* and checking?
     
  3. big gear head

    big gear head Veteran Member

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    What gear ratio did you put in it? Sometimes when you go to something like a 4.10 the drive shaft speed is too much for the stock drive shaft. No matter how many times you balance it the shaft will start to bow at highway speed and cause a vibration. The only fix is to get a new heavy duty drive shaft.

    If you had a pinion bearing problem I think you would be able to feel it when you turned the pinion with the drive shaft out.
     
  4. LT1 WS6

    LT1 WS6 Veteran Member

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    3.90 gear ratio. I didn't think about terminal speed. It is a factory shaft that I had shortened when I did the engine and transmission swap.

    You're also correct I had forgot to mention that the pinion rotates smoothly when turned by hand.

    I have not swapped the driveshaft around, Corky.

    Thanks guys!
     
  5. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Is it more obvious when you are cruising at a steady speed?
    (Little to no torque against the u-joints)

    A yoke slightly off center (or the ears splayed) will vibrate like that even though everything else is perfectly balanced and true.

    Make sure there is no side-to-side play in both u-joints. (Not rotational "slop" ... End play in the caps.)
     
  6. LT1 WS6

    LT1 WS6 Veteran Member

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    It does change a little between accel, cruise, and coast. It doesn't get worse as I go faster just changes a little. I've gone through 6* of sweep changing the pinion angle of the rear. No change at all changing 2* degrees each step.

    When I put the new rear u-joint in, it didn't go smoothly. I used a c clamp and had to crank hard. The joint was stiff but rotated smoothly once in place. I thought for sure this would show some change even if to the worse side, but that would at least tell me I'm in the correct area. It didn't change anything one iota. Old u-joint came out easily and rotated easily.

    If I did my math correctly, with 26 inch tall tires, driveshaft speed is 3000 rpm at 60 mph. Too much?
     
  7. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    I doubt it's a pinion angle problem.

    Forcing a U-joint home is how I splayed a yoke.
    (I had a needle bearing tipped over in the cap.) :mad:

    Your math is probably good with a 1:1 drive gear and 3.73 rear.
     
  8. jthomas

    jthomas Veteran Member Lifetime Gold Member

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    I had a similar vibration recently from 72-80 mph. 3:73 gears, 26.8" rear tires. Started getting worse after I got new tires and balanced. Turns out shop did a static balance on them. Tried the simply stuff first and took them to a new shop in town with a nice new dynamic balancer. Guess what? WAY OUT OF BALANCE. they fixed me up and vibration is gone. The old balance had a few weights in middle of rim. New shop had some at inside hub and some on inside edge of rim. That made the difference.

    Another possibility. When ujoints go in hard, depending on how you forced them in, you may have bent the driveshaft ears slightly. Check the runout on the driveshaft. I bet you will find its beyond spec. If you have a dial indicator it's an easy check. That can cause a harmonic vibration at certain speeds, usually higher speeds.
     
  9. bigdav160

    bigdav160 Veteran Member

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    60mph is more likely tire related than driveshaft related. Driveshaft vibration is lower (25-35mph) or higher (80+)
     
  10. LT1 WS6

    LT1 WS6 Veteran Member

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    Rear tires are brand new and balanced using road force machine. Even with the tires swapped front to back the vibration is the same. The vibration is present even when the axles are removed from the car.

    I hate throwing money at a problem because I don't necessarily learn anything. That being said, I'm tempted to just get a new driveshaft anyway. Mine's a touch shorter than I'd like it to be. When I first did the engine and transmission swap, the rear suspension was stock and worn out. Since that time, I've put the new suspension in and it actually raised the rear just a small amount. No idea if this could be the problem though.

    Thank you for the replies.
     

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