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Pinion Angel?

Discussion in 'The Hokey Ass Message Board' started by miller, Mar 15, 2013.

  1. miller
    Joined: Aug 5, 2006
    Posts: 501

    miller
    Member
    from New Jersey

    As it appears...when the trans is higher then the rear...the trans points down and the rear points up...if that is correct and I know it is...how does it change when the trans is LOWER then the rear?...would it be trans up and rear down and still staying with in the allowed safe degrees?....I was at a car show and I seen a car where the trans was lower then the rear......Miller
     
  2. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    I build cars with the pinion yoke above the transmission output shaft, all of the time. The parallelism theory still applies, just the same. You want equal, opposing angles, to cancel out velocity changes inherent in the design.

    U-joints do not rotate at a constant velocity when at an angle. Because there are 2-planes of movement, there are two distinct accelerations and decelerations in the operational velocity, per rotation. Keeping the angles equal and opposing, on a 2-joint shaft, nearly completely cancels out the the changes in velocity, making for a smooth, or smooth enough operation.

    Get those angles too extreme, or unequal, and the velocity changes will not be cancelled out well at all, and you will have vibration. Some vibration is inherent in the design, but that is minimal, and mostly dampened out by the suspension bushings, engine and transmission mounts.

    I hear all of the time from people that they are running extreme, or unconventional setups, and that they are "totally fine". My equipment shows otherwise. Just because the vibration is not making it all the way into your butt, does not mean that it is good for the shaft, the u-joints, or anything else attached, therein.
     
    Last edited: Mar 17, 2013
  3. Gimpyshotrods, your explaination on this subject is the best i've seen so far. I'm experencing what i think is a problem with the pinion angle on my '55 right now. The pinion angle looks to be 7 to 8 degrees "up" and the transmission appears to be 3 to 4 degrees "down". I am experencing a recurring vibration at 60-70 mph. The u-joints are in excellent condition so i am going to try shimming the pinion angle down to try to match the transmission in hopes it will eliminate most if not all of my problem.
     
  4. blown496
    Joined: Nov 16, 2011
    Posts: 2

    blown496
    Member

    This is the best document on drive line angles. http://www.iedls.com/asp/admin/getFile.asp?RID=10&TID=28&FN=PDF I fought mine with a 60-65 vibration until I finally had the tires load balanced on a Hunter machine. I worked with a fellow engineer who could deliver a presentation on electronic and computer theory and build stuff that blew our minds. I had to spell check and write all his papers because his spelling was horrible. Spell check helped but he still had me proof read it. So a genius can be lurking behind those words and I try to look at what the person is saying rather than how it look what they are saying. End of speech.:)
     
  5. BillyM
    Joined: Feb 9, 2010
    Posts: 144

    BillyM
    Member

    Just my humble opinion, but I think you can distinquish tire vibration from driveshaft vibration by the frequency. I fought with a 65+ mph high frequency vibe in my (OT) Swinger - balanced everything I could think of, finally (in hindsight - dummy) checked the pinion angle and found it to be about 6-7 degrees up (up toward the tranny). The previous builder had installed a DC offset spring kit and must have welded the relocated spring perches at a bad angle. I shimmed the perch/spring connection and virtually eliminated the vibe. One of these days, when I get ambitious, I'll cut them off and reweld them properly. In my case, I'm convinced that it was further aggravated by my small tires (14") and fairly high (3.91) rear gear ratio - which results in a fast spinning drive shaft.

    Moral of the story? Yes, it's important for the two center lines to be parrallel!
     
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  7. Russco
    Joined: Nov 27, 2005
    Posts: 4,327

    Russco
    Member
    from Central IL

    I had a thread a few days ago about setting my leaf spring car up 2* down from paralell to compensate for the pinion climbing under acceleration (its going to see some strip action on weekends too) and it wasnt very well received. Now a 4 link or ladder bar car with good bushings isnt going to move much at all and for a street car I would agree that just keeping them parallel is right if they start of angled up from parallel its only going to get worse.

    Here is an example of what happens on leaf springs. To me that looks like a good 5* or more
     
  8. suedestude
    Joined: Feb 15, 2004
    Posts: 106

    suedestude
    Member

    Gimpyshotrod, Thanks man you just helped me out.Ive been in hot rods for years and I could listen to you for hours.
     
  9. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    I get boring, after a while.
     
  10. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    If your pinion is climbing a full 5º on acceleration, you ought to be searching for a way to limit spring wrap, rather than simply jacking the pinion down to compensate. Simply adjusting the pinion down leaves it in the wrong, or less than ideal position, almost all of the time, during normal operation. This is fine in a vehicle that sees the world 1320 feet at-a-time, but very hard on drivetrain that has to make its way in the real world.
     
  11. TerrytheK
    Joined: Sep 12, 2004
    Posts: 1,273

    TerrytheK
    ALLIANCE MEMBER

    ARRGGGHH! My head hurts!!

    Seriously, thanks for your insight. This is a timely subject for me. I'm in the middle of a project that may involve re-setting a pinion "angle" and this confirms what I've been doing all these years. Nice to know that for once I ain't totally wrong... :)
     
  12. Ralphies54
    Joined: Dec 18, 2009
    Posts: 772

    Ralphies54
    Member

    Gimpyshotrods,you the man. My pickup has a C4 rear solidly mounted at 3 degrees up and the engine mounted at 3 degrees down, in other words pointed straight at each other with out any offset. Im chasing a slight vibration but can't tell yet if it's engine, wheel or angle problem. Is my driveline OK without anyoffset? Thanks, Ralphie
     
  13. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    As long as the u-joints are in good shape, and the shaft is balanced, and not bent, your setup should be just fine.

    Check your transmission mount. I can't tell you how many "driveshaft issues" were actually a worn/loose/broken transmission mount. Inspect all bushings and mounts. Look for shiny/bare spots on any metal parts that are within about 1/8" of each other.

    When, exactly, does the the vibration occur, and where does it feel like it is manifesting? Accelerating? Decelerating? Certain speed range? All of the time, when in motion?
     
  14. Ralphies54
    Joined: Dec 18, 2009
    Posts: 772

    Ralphies54
    Member

    thanks for the reply. It seems to be about 1800 RPM or 60-65 MPH. Ralphie
     
  15. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    Ahh, the dreaded 60-65 MPH vibration. This is a common range for sympathetic vibration from a number of possible causes. Rotate the front tires to the rear, and vice versa, if you can. Have the rears, or better, all of them, road-force balanced. Ask for that, by name. There should be plenty of shops in the 413 that can do that.
     
  16. Ralphies54
    Joined: Dec 18, 2009
    Posts: 772

    Ralphies54
    Member

    It was suggested that maybe the halfshaft u joints might have a problem? But how would I check that? Thanks again
     
  17. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    Your truck should have just the two conventional u-joints. Only front wheel drive, all wheel drive, 4x4 vehicles, and vehicles with independent rear suspension have half-shafts.
     
    Last edited: Mar 17, 2013
  18. Russco
    Joined: Nov 27, 2005
    Posts: 4,327

    Russco
    Member
    from Central IL

    I set mine up only about 1.7* down from parallel. I kind of split the difference. I dont know how much mine will change my car isnt finished yet and I do plan on running some Caltrac bars on it. They recommend 4-5 degrees down(for street/strip cars) and more for all out drag cars, he said he has some cars running close to 10* down to compensate for movement. I figured at 2* or less, when it moves alot I'll be closer and under easy driving conditions it wont be off by enough to matter much. Im kind of suprised though you said you have never seen one change more than 2.5* though, that video I posted is just a stock Ford Lightning pickup truck although its kind of fast for a pick up its no where near 600 ft pounds of torque. They come from the factory with a little down angle ( .6) to compensate for the wrap too. The reasearch I've done just checking around and talking to Calverts on the phone it seems its a pretty common practice to set them up this way. I thought Id try this and see how it works having a little bit of a racing background. I cant just leave well enough alone I guess.
     
    Last edited: Mar 17, 2013
  19. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    Most of the stuff I work on will break the tires loose way before the springs can wrap up more than 2.5º. Bias-ply Firestone repros are the norm 'round here. A pair of 6.70-15's won't hold back much torque before they start squealin'.
     
  20. Russco
    Joined: Nov 27, 2005
    Posts: 4,327

    Russco
    Member
    from Central IL

    Ive made a few passes down the 1/8 with some Coker L78/15 bias plys, they never did hook up the entire time I was on the gas. I bought a set of those Pie crust slicks but they are the heaviest automobile tire I think I've ever seen. Not good either.
     
  21. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,229

    EnragedHawk
    Member
    from Waco, TX

    This turned out to be a great read through; I learned a lot.
     
  22. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,229

    EnragedHawk
    Member
    from Waco, TX

    Probably a stupid question; what happens in the case of a two piece drive shaft? Are parallel centerlines still needed?
     
  23. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    On the rear section. The front section should be in-line with the output shaft, less 1º, to make sure that the needles move in the caps, and don't gall:

    [​IMG]
     
  24. EnragedHawk
    Joined: Jun 17, 2009
    Posts: 1,229

    EnragedHawk
    Member
    from Waco, TX

    Cool, thanks for the information!
     
  25. isky1843
    Joined: Feb 3, 2011
    Posts: 157

    isky1843
    Member

    gimpyshotrods- what would you say about a transmission that is 1-2* up and a diff that is 1* down? The engine has front mounts and then the bellhousing mounts on the crossmember. The engine can't come up in the front anymore without the distributor hitting the firewall. The pinion was down about 5* so I shimmed it up to only be 1* which is close to being parralel with the crank centerline. This got rid of a good bit of the vibration, but it now vibrates pretty good at 70mph plus. What are your thoughts?
     
  26. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    Please clarify. As written, your transmission yoke is pointed up toward the sky, and your pinion yoke is pointed down at the ground. Is this the case?
     
  27. isky1843
    Joined: Feb 3, 2011
    Posts: 157

    isky1843
    Member

    That is the situation. I have the front of the motor as far up as I can before the distributor hits the firewall. This puts the tailshaft at positive 1* mabey just a touch more. I shimmed the rear end to be equal but opposite which is negative 1*. The thinking behind this is that it should still function the same, it will just have more overall driveshaft angle. This rear end is going to be coming out in a few months to replace the leafsprings with a coil spring, truck arm suspension. At that time I will clearance the firewall so that I can get a proper neg 1* at the tailshaft, and then set up the new rearend accordingly. Untill then I am trying to figure out if this is the source of my vibration above 70. Driveshaft was built and balanced recently but I'm not completely ruling that out. U-joints are new, I am starting to think about having my pressure plate balanced.
     
  28. ANDEREGG TRIBUTE
    Joined: Jan 1, 2008
    Posts: 1,385

    ANDEREGG TRIBUTE
    Member
    from Bordertown

    thank you!!!!

    I will be setting mine up accordingly:D

    Maybe...gimpy....you should change your name to "pinion angel"....lol
     
  29. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,263

    gimpyshotrods
    ALLIANCE MEMBER

    Just keep in mind, if your angles are going to end up beyond acceptable limits on that setup, it will be necessary to depart from the convention 2-joint configuration, and move to a 3-joint shaft, with a double-cardan setup, at the transmission end. Mock it up, and figure out what your joint angles will be, and post them.

    Like this, just with the axle above that tail shaft:[​IMG]
     
  30. 29AVEE8
    Joined: Jun 28, 2008
    Posts: 1,384

    29AVEE8
    Member

    gimpy.

    In the double-cardan set up as depicted above, do you still need some working angle on the rear u-joint?
     

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