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Driveline Vibration Problem

This is a discussion on Driveline Vibration Problem within the Manual Transmission forums, part of the Drivetrain category; Ok I need help. I've been upgrading the suspenssion on my TA. Here's what's done so far. 35mm (front) 25mm ...

  1. #1
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    Driveline Vibration Problem

    Ok I need help. I've been upgrading the suspenssion on my TA. Here's what's done so far.

    35mm (front) 25mm (rear) swaybars
    Eibach pro kit springs
    KYB shocks and struts
    tubular lower control arms
    adj panhard bar
    subframe connectors
    strut tower brace
    Spohn torque arm

    With that I've also swapped the 10 bolt for a Strange S60 about a year ago. Everything was working fine till I put the new torque arm on. Now I have a god awefull vibration. I adjusted the pinion the way the instructions said to do it initially, but it felt like the drive shaft was going to fly out in 4th gear. I then proceeded to do the proper way of setting the pinion angle. Took the DS out and read the angle on the tail shaft and adj. the pinion to reflect the opposite -1. It now doesn't start vibrating till around 5,000 in 4th and about 3,000 in 5th, and 5th has the worst of the vibration. 1st, 2nd, 3rd, and 6th are ok, no vibration. I tried -2, -3, and 0, but all got worse when doing so. I know with that type of torque arm there are going to be more noise and vibrations, but not like car's about jettison the drive shaft. Does anyone have an idea how correct this problem?
    Last edited by AborTivE; 12-08-2008 at 11:09 AM.

  2. #2
    The Bandit Wesman's Avatar
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    The issue you are describing doesn't really make much sense.

    Any driveline vibration rearward of the transmission is entirely dependent on speed. Meaning generally the faster you go, the worse the vibration gets. The gear you are in will not affect it.

    Since you say its only in certain gears, it would almost have to be an internal transmission problem. However, that is very unlikely, because if there was internal transmission damage, you would be having shifting and engagement problems, which you didn't mention.

    The first thing I would check it the driveshaft. Remember, any sort of vibration at speed must be caused by a rotating assembly. So if you adjusted the pinion angle and it got worse, you have narrowed it down to the driveshaft.

    What was your measurement for your driveshaft angle on the trailshaft?? First thing I'd do it inspect the u-joints for wear and check the straightness of the driveshaft. I had a bad vibration at higher speeds in my car, turned out my driveshaft was bent.
    1998 Trans Am WS6 SGM
    Lid, Pro 5.0, WS6 Short Stick, LS7 Clutch, TB Bypass, Detroit TrueTrac, Poly Mounts, Bilstein Shocks, LS6 Intake, SFCs, CTS-V Brake Upgrade, STB, Nitto 555's. SS Longtube Headers and True Duals w/ H pipe and Magnaflows. Tuned by Harris Speed Works. 341.4WHP/346.1 lb/ft.

  3. #3
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    It starts around 70mph and gets worse from there... until you put it into 6th. I really don't know why it smooths up in 6th, but it does. When I was changing pinion angles the vibration would move to other gears. At one angle it would start vibrating in 3rd, and another it moved to 5th and 6th (yeah 6th wasn't smooth that time, lol).

    The only shifting problem I have is the normal 2-3 at high RPMs. I know what's causing that, and will be the next thing I work on after i figure this thing out.

    I know the torque arm/pinion angle has to be the problem, because everything was working right, but it magically went to hell after I put the torque arm on, and I'm sure if I put the old one back on it'll heal it. There's gotta be something I'm missing though. I'll probably go in and replace the U Joints anyway, just because the car don't seem right, and I'm sure that with it not, it is probably messing them up.

    The tailshaft measured +3... weird to me, most cars are neg on the tailshaft aren't they? So I went -4 on the pinion. This is the first time I've ever set a pinion. What is the factory tailshaft angle supposed to be? Maybe I messed up somewhere. The car was at ride height and level when I took the measurement. It was pretty hard to see up to the top of the tunel to read it. Thanks for the help BTW
    Last edited by AborTivE; 12-02-2008 at 07:40 AM.

  4. #4
    The Bandit Wesman's Avatar
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    Quote Originally Posted by AborTivE View Post
    It starts around 70mph and gets worse from there... until you put it into 6th. I really don't know why it smooths up in 6th, but it does. When I was changing pinion angles the vibration would move to other gears. At one angle it would start vibrating in 3rd, and another it moved to 5th and 6th (yeah 6th wasn't smooth that time, lol).

    The only shifting problem I have is the normal 2-3 at high RPMs. I know what's causing that, and will be the next thing I work on after i figure this thing out.

    I know the torque arm/pinion angle has to be the problem, because everything was working right, but it magically went to hell after I put the torque arm on, and I'm sure if I put the old one back on it'll heal it. There's gotta be something I'm missing though. I'll probably go in and replace the U Joints anyway, just because the car don't seem right, and I'm sure that with it not, it is probably messing them up.

    The tailshaft measured +3... weird to me, most cars are neg on the tailshaft aren't they? So I went -4 on the pinion. This is the first time I've ever set a pinion. What is the factory tailshaft angle supposed to be? Maybe I messed up somewhere. The car was at ride height and level when I took the measurement. It was pretty hard to see up to the top of the tunel to read it. Thanks for the help BTW
    Thats very strange how the vibration changes depending on gear selection.

    Sounds to me like you are going about setting the pinion angle incorrectly. You are right about using opposite angles, meaning if your trans has a negative 2 degree angle, you want the pinion on the diff to have a positive 2 degree angle. In this way, they become cancelling angles, which offset each other. As one u-joint accelerates the other is decelerating (due to the fact that u-joints travel in an ellipse as they make one complete revolution), so the vibration is minimized.

    Your problem is that you have a positive angle (for some reason?) on the tailshaft. So instead of having cancelling angles, which effectively subtract the difference of one from the other (2-2=0) you are adding the angles, since the tailshaft is angled up and you are angling the pinion downward. So instead of having a difference of 1 degree (4-3=1) you have a difference of 7 degrees (+3-[-4)= 7). And thats where you are inducing the vibrations. Try setting the pinion at 0 and work your way upwards from there, in a positive direction. I can't promise it will help, but its worth a try, because going in the the direction is just making matters worse. I think you may need to figure out why the trans is angled upward instead of being level or angled slightly downward, thats where your issue originates.

    Good luck, I believe we've found your problem

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    Roger that. I'll get to work to see what I can do. I'll keep you posted. Thanks again.

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    Ok, so I started messing with it again. Spent a day trying to figure it out. I tried one more thing as it set.... no avail. So I took the DS back out and checked the tailshaft angle again. Yeah... so I realized I read the angle wrong in the first place, lol. It was -3 instead of +3. So I 0'ed out the pinion angle and took it for a test drive. It seemed to help, but encountered a new problem. This I believe is important for anyone running a S60 and the spohn torque arm on a lowered car. After I raised the pinion and test drove it the DS was rubbing on the E brake splitter mount. Yeah, let me tell you there's alot of things I can handle and fingernails accross a chalk board is not one of them, and that's pretty much what it sounded like. I got it back into the garage and shimmed up the tailshaft and lowered the pinion. It's better but I need to get back under there and yank the DS and see what the real tailshaft angle is and reset the pinion again. I'll let you know how it goes.

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    This is an old thread and you may have already solved the problem, however this may help in the future.
    Both the transmission tail shaft & the pinion shaft, under ideal conditions*, should be set parallel to one another.
    The distance between the two parallel lines should not result in the drive shaft angle to connect the two being grater than -15 at the tail shaft & +15 at the pinion shaft for a drive shaft with 2 U joints.
    *however because the rear end is sprung it tends to rotate the pinion shaft upward under acceleration. To counter this rotation the pinion shaft should be set at -1/2 to -1 degree from being parallel with the transmission tail shaft. (even with a solid torque arm the differential is still going to rotate up)

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    Boy I hate when I don't get to hear how a problem worked. This one seems very interesting.

    Night Move made a good addition for offset it would seem.

    But I think Wesman knocked it out of the park.

    Note: I think the gear differences in the vibration was due a little to engine load and xmission load (translating more through the box to the front end). But mostly due to frequency alignments, that being harmonic modualtion with the engine rotation and natural vibration at certain rpms.

  9. #9
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    Well I got it as close as I can. I had to space the tailshaft up so I could lower the pinion down more to keep the drive shaft from rubbing on the E brake splitter mount. Set the pinion -2, and now it's better. Under hard excelleration you don't feel it as bad as it was, or as soon as it was. I talked to Strange Engineering, and the tech said that he had a crap load of calls about that. He said that it just seems to be the nature of the beast with those. He also said that a lot of the people that put that kind of tourqe arm on usually take them back off because of the vibration. The car is smooth durring normal driving, and don't notice the vibration until it's under heavy excelleration. I still don't like feeling everything through the drive line, but now that I know that it's just the way it's going to be makes it not bother me as much as it did when I thought that something was really wrong.

    The arm is good, but if you get one, you better be able to handle the vibration that comes with it... oh and the frustration of getting it set right (if the car is lowered) too, lol.

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