Driveline angle issue?

Discussion in 'Transmission & Driveline Topics' started by ULTM8Z, Dec 1, 2019.

  1. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

    Messages:
    8,883
    Likes Received:
    21
    Joined:
    Dec 8, 2000
    Location:
    Republic of Texas
    I wouldn't cut that brace out on a frame car, much less a unibody. They already twist and give a ton as it is.
     
    hubedobeedo and G72Zed like this.
  2. G72Zed

    G72Zed Veteran Member

    Messages:
    1,245
    Likes Received:
    295
    Joined:
    Sep 8, 2015
    Location:
    Canada
    For all the work and expense of the GV unit you have committed too thus far, and in order to correct & improve your current drive line geometry issues, I would suggest you have the floor properly clearance'd and reinforced/boxed by a professional (that's if your not comfortable in doing this yourself or lack the tools & skill set)

    I think the effort is worth it at this point.
     
    Last edited: Dec 6, 2019
    hubedobeedo likes this.
  3. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

    Messages:
    8,883
    Likes Received:
    21
    Joined:
    Dec 8, 2000
    Location:
    Republic of Texas
  4. ULTM8Z

    ULTM8Z Veteran Member

    Messages:
    9,209
    Likes Received:
    365
    Joined:
    May 19, 2000
    Location:
    Los Angeles
    I don't know... the guy is running 700 hp and slicks... not sure what's going on with his car. Sounds like he was beating on it pretty hard. I'm not really beating on mine with drag racing and stuff. Just a street car having a little fun with 8 speeds. But so far it's running great.

    But back to my driveline angle thing...

    So I put in the 4° shims and it *seems* like it got a little better. But I still have the vibration. Using the Tremec app, it's saying my driveline angles are just right in the static condition. Wondering if I need to go to 6° shims to get a little "head start" on the axle wind up? Maybe the shorter driveshaft is more sensitive to this stuff?

    It definitely feels like it's coming from the rear of the car though. But it only does it in first gear and under hard throttle. With every other gear I don't get any vibration.

    Only thing is, as I'm thinking about it though the frequency of the vibration almost seems like it's too high for the speed I'm at coming off the line. But the problem is I dont know what else could generate a vibration only in first gear under hard throttle.

    If the 6° pinion shims don't solve it, what else should I be looking at?
     
    Last edited: Dec 15, 2019
    hubedobeedo likes this.
  5. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

    Messages:
    14,956
    Likes Received:
    1,423
    Joined:
    Nov 2, 2002
    Location:
    Waddell AZ
    Except for smoking the trany, right?
     
  6. ULTM8Z

    ULTM8Z Veteran Member

    Messages:
    9,209
    Likes Received:
    365
    Joined:
    May 19, 2000
    Location:
    Los Angeles
    Dave, What would be in the transmission that could generate a vibration like that only in first gear and only under hard throttle? But work perfectly everywhere else?
     
  7. biker

    biker Veteran Member

    Messages:
    975
    Likes Received:
    111
    Joined:
    Dec 7, 2014
    Location:
    New Liskeard Ontario Canada
    So if you slowly sneak up on the top end of first gear, no vibration right? Can u hold 5000rpm in first gear for 15 seconds or so and no vibration?
    If so, and acceleration is the only condition that causes it, its gotta be drive shaft angle altered by axle windup. Any way to temporarily clamp/lock your diff in place just to diagnose? Cheap traction bars maybe? I don't like them either, but just an experiment to see what happens.
     
    xten likes this.
  8. ULTM8Z

    ULTM8Z Veteran Member

    Messages:
    9,209
    Likes Received:
    365
    Joined:
    May 19, 2000
    Location:
    Los Angeles
    So I took it out for another test drive...

    Yeah, anything below roughly ~1/2-3/4 throttle, no vibration whatsoever. Launches perfectly. I can do anything I want within that range and not get any vibration, noises, etc. Transmission has absolutely no problem putting power to the ground.

    If I floor it, what *seems* like it's happening is when the tires break loose the vibration intensity goes down... then as it gets into a little wheel hop (with the tires grabbing intermittently) the vibration starts coming in and out. Almost like when the tires lose grip, the reaction forces between the tire and the ground give out and the axle wrap relieves itself, thereby allowing the pinion angle to momentarily go back to normal.

    I don't know... maybe my hopefulness is causing me to imagine it. It's happening so fast it's hard to pinpoint.

    I'll I know is I don't get hint of vibration or noise anywhere else and the transmission performs flawlessly everywhere.

    I can get the 6° shims pretty cheap from Summit, so I may just try them. Maybe the shorter driveshaft is just less forgiving of adverse driveshaft angles and needs more "help".
     
  9. biker

    biker Veteran Member

    Messages:
    975
    Likes Received:
    111
    Joined:
    Dec 7, 2014
    Location:
    New Liskeard Ontario Canada
    All that points towards controlling your axle windup. A good set of leafs that resist windup and either let the tires spin or hook without rotating the axle would likely solve things. If your driveshaft is set up perfect for angles now, I wouldn't mess with it to fix a condition that is 10% of your driving and potentially negatively impacts the other 90%.

    Caltracs or good leafs should fix the acceleration issue. Considering what u have into the car and how much you enjoy it, I'd be all over that solution.

    Again though, a quick test with something to stabilize your axle would make the decision easy. Although, you have pretty much done that by narrowing it down to a condition that can really only be axle wrap.
     
  10. ULTM8Z

    ULTM8Z Veteran Member

    Messages:
    9,209
    Likes Received:
    365
    Joined:
    May 19, 2000
    Location:
    Los Angeles
    You may be right... though I'm not to keen on stiffer springs as I like the current ride quality. Also not to keen on the look of a lot of these traction devices hanging off the bottom of the springs...

    What's the lowest profile traction device that's out there?
     
    hubedobeedo likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.