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Thread: Help please with a chassis question

  1. #1

    Help please with a chassis question

    Ok at the track this past weekend I had what seemed to be tire shake but it didn't spin. It just vibrated on the launch and then cleared up. This has had me puzzled and can't figure it out. First I thought it may be the pinion angle but others on another site don't think that is the problem that most of the time improper pinion angle will cause problems on the upper end of the track. Right now I have +3 on the rearend and -4 on the transmission so this would make my pinion angle -1. What are your opinions on this? Just picture the first 100' feeling a vibration like a tire shake or something and then just clear up after the 100'.

    This is a 1984 Chevy S10 stock suspension with Slide-A-Links, Calvert Racing Mono Leafs, Rancho 6000 rear adjustable shocks with 12 settings, front is QA1 "R" Series coil overs. BBC615 Big Chief engine with 3 stages of nitrous. This weekend was first pass out and was on motor only and NO spray.

    All help will be greatly appreciated.

  2. #2
    Senior Member DYNO OPERATOR
    Join Date
    Aug 2005
    Location
    Rifle Colorado
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    585
    How bad was the vibration? The only time I've experienced tire shake was in my old FED. It rarely shook, but when it did, it wasn't at the hit. It was usually when the front end touched down and it hurt!! I'm talking about teeth rattling, vision blurring shake. It didn't last long (thankfully) but it wasn't just a vibration. Tire shake isn't spinning. It's the tires wadding up and trying to run over themselves. A little spin would be much better.


    I'd think with that much torque and a leaf spring suspension, you really need more down angle on the pinion. Probably to the tune of 4-7 degrees down from the driveshaft at rest to be straight under power....

  3. #3

    Vibration

    The vibration wasn't teeth chattering but noticable enough that I could feel it good but approx. 100' out it went away everytime at about the same point and the truck would be smooth except for a steering issue that I had. It was a feeling I have never felt before and just didn't feel right. I may jus be overreacting to this whole new big block build but it just didn't feel safe on take off but after approx. the 100' out it felt real good.

  4. #4

    Pinion angle

    What is your theory as to what pinion angle will do whether it be too much or not enough? I am in a new ball game with this build so trying to learn everything I can. Thanks for the help.
    Thanks
    Travis
    www.s10dragracer.com

  5. #5
    Senior Member DYNO OPERATOR
    Join Date
    Aug 2005
    Location
    Rifle Colorado
    Posts
    585
    Without enough down angle, the pinion may be rotating far enough to cause the ujoint to bind, causing the vibration. Most leaf spring suspensions rotate a bunch. With a big tire/really good traction, and a bunch of torque, it'll be even worse...

  6. #6
    Don't forget to check the easy stuff, too. If your tires aren't spinning, maybe your clutch assemblies in the trans are chattering. Is the fluid burnt? May not be this, but it couldn't hurt to check.

  7. #7
    Senior Member MASTER BUILDER
    Join Date
    May 2003
    Location
    Owingsville, Ky
    Posts
    157
    I would also make sure of the driveshaft length to verifyol that it isn't bottoming out when the truck squats. As stated earlier, with leaf springs you will want the pinion angle to be 4* or more especially with the mono leafs, since they will allow the rear end to twist more.

    Bill M

  8. #8
    Member MASTER JOURNEYMAN
    Join Date
    Mar 2003
    Location
    Leavenworth, Kansas
    Posts
    35
    Could it be tire pressure? You Might want to put a little more in and give it another shot.


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