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argument about the purpose of CV driveshafts

Discussion in 'The Garage' started by four_by_ken, Dec 2, 2004.

  1. four_by_ken

    four_by_ken 1/2 ton status

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    The argument was that the only real purpose for a CV shaft is to eliminate vibrations. They dont relaly gain much more angle if any.

    If the vehciel is rarely driven on the street, a CV isnt really needed.

    Whats the truth to this? /forums/images/graemlins/confused.gif
     
  2. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    The reason a CV removes vibrations is soley because it CAN handle more angle than a standard u-joint. People will tell you you need one and some won't. I have about 6.5" of suspension lift in the rear and when I had my rear shaft built I wanted a CV but the driveline guy said I didn't have enough angle to require one. I just went with a 1350 slip yoke and complete 1350 4" shaft. I couldn't be happier.
    [​IMG]
     
  3. four_by_ken

    four_by_ken 1/2 ton status

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    It handles more... or it handles the angle better. There is a differance. If my truck ever sees over say 55mph... I am shocked.

    I think for cost reasons, I am going to go without the CVs with 8 inches of lift.
    /forums/images/graemlins/eek.gif

    I keep seeing guys at the bogs in shortbeds with no CV and more lift than I have. I will try it and see what happens I think.
     
  4. K5MONSTERCHEV

    K5MONSTERCHEV 1/2 ton status

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    [ QUOTE ]
    The reason a CV removes vibrations is soley because it CAN handle more angle than a standard u-joint.

    [/ QUOTE ]

    Yeah, they let you run at more of an angle. I don't think my truck world wokr without a CV.

    As to handles more. Handles more what?
     
  5. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    if you're cheap, get a junkyard shaft that has a big CV joint on it and have a shop incorporate it into your existing shaft. I think a lot of people set up a non-CV shaft and look at it in the driveway and think "that angle doesn't look to bad" and go with it. What they aren't thinking about is what happens down the road when their suspension gets a LOT more flex to it and they're out wheelin and their suspension is really drooping. Lot more angle than when sitting in the driveway... they get in a tough spot, hammer the gas and their u-joint is operating at or above its maximum normal working angle. pop, boom, bang! there goes a u joint. There are definitely applications where a CV aren't needed, Im just saying that when you decide to go without one, consider where your rig is going and what your suspension will be doing under hard use... then you'll know if you need one or not.

    j
     
  6. R72K5

    R72K5 Banned

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    sounds like yopure safer to have CV joint rather than not ot have it

    good luck
     
  7. four_by_ken

    four_by_ken 1/2 ton status

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    No, I am not cheap. /forums/images/graemlins/rolleyes.gif

    In fact everything I use is new. I just am not going to spend the money on CV shafts if it doesnt warrent them.

    I will test my droop and angles before I take it out and hammer on it. /forums/images/graemlins/rolleyes.gif

    I am just going my previous personal friends experience and also looking at my angles.

    The rear is plenty long and at good angles(I think 20 right now) as to not need a CV. The double lengthened the front enough that I think I am fine.

    We'll see.
     
  8. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I run one , just because it was easier and I wouldn't need shims . My pinion points straight at my case with shackle flip . It does make a big difference on freeways , it actually cruises pretty quiet for a fullsize 21 year old truck with larger than stock tires . With it the right working length I have yet to have a problem flexing or anything . It prolongs the life of all u-joints , but you can still break one or have one go bad due to torque etc , just like with any shaft /forums/images/graemlins/k5.gif /forums/images/graemlins/k5.gif
     
  9. four_by_ken

    four_by_ken 1/2 ton status

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    [ QUOTE ]
    sounds like yopure safer to have CV joint rather than not ot have it

    good luck

    [/ QUOTE ]

    For arguments sake... why do you say that?
     
  10. muddog

    muddog 1/2 ton status

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    straight from the ole book "The constant velocity joint on the drive shaft is used to eliminate all harmonic vibrations that are associated with a traditional u-joint that is required to speed up and slow down in a complete revolution."
     
  11. rcurrier44

    rcurrier44 1/2 ton status

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    [ QUOTE ]
    straight from the ole book "The constant velocity joint on the drive shaft is used to eliminate all harmonic vibrations that are associated with a traditional u-joint that is required to speed up and slow down in a complete revolution."

    [/ QUOTE ]

    2 u-joints (one on each end of the shaft) running 180 degrees out of phase do exactly the same thing....Infact this is all that one of the CV's you all are thinking about are. Many CV's (like some toyota d-shaft CVs) have a lower operating angle than the u-joints on the other end of the shaft.

    I think the big advantage of a CV is that it allows you to tilt the pinion up (witch needs to be done for it to work properly). In tilting the pinion up you can easly gain 2-3 inches of height at the pinion...therefor making the drive shaft angle less and keeping the u-joint/pinion farther away from the rocks.
     
  12. four_by_ken

    four_by_ken 1/2 ton status

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    Hehe... more conflicting opinions. /forums/images/graemlins/rotfl.gif

    I still think you dont get anymore angle with a CV, no one has proven this.

    Having the pinion rotated up requires a CV shaft? Anohter disagreement I have heard answered both ways.

    /forums/images/graemlins/confused.gif
    /forums/images/graemlins/dunno.gif
    /forums/images/graemlins/screwy.gif
     
  13. drivelineman

    drivelineman 1/2 ton status

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    i can tell you our c/v gets better angle than 1310 non c/v and 1350 non c/v both 20 degree's max 1350 - 25 max 1310- and 1410 is close 28 degree's - but all the non c/v shafts are going to vibrate with angles more then 15 degree's operating - our 1350 c/v gets 32 degre's - there you go- hope this helps- Jesse
     
  14. rcurrier44

    rcurrier44 1/2 ton status

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    Its amazing how many people don't know how a u-joint/drive shaft works /forums/images/graemlins/deal.gif

    A u-joint velocity output constantly varries like a SIN wave. This is what creats the vibrations. The working angle of the joint determines the height of the "wave" and the "wave" repeats itself every revolution of the shaft. If you have another u-joint on the drive shaft rotated 180 degrees and working at the same angle in relation to the first joint it has the exact opposite changing velocity output...when plotted it looks exactly the opposite of the sin wave. Therefor when used like this as one u-joint is speeding up its output velocity the other is slowing down its output velocity. This results in smooth transfer of power to the rear wheels and low vibrations from your drive shaft.

    When using a cv that has 2 ujoints in it these 2 ujoints are placed 180 degrees out from eachother just like above (hence the name Constant Velocity). So now that your CVjoint has canceled out the changing velocitys at one end of the drive shaft you don't want any angle at the other end of the drive shaft causing vibrations. So you tilt your pinion up so it is inline with the drive shaft...graphicly this is like taking all the height out of the SIN wave. In reality since you will get some axle wrap/climb under load you should have the pinion pointed just below the shaft (in the rear - just above in the front) so as it comes up under power it is aligned with the drive shaft. On most trail-only rigs or on a front drive shaft its not a big deal because your only spinning the shafts at low RPMs. But on the road at higher speeds you can realy feel the difference.

    "Getting more angle" out of a CV is realy going to depend on witch CV you use. In theory since your CV uses 2 u-joints then you should have twice the working angle. The problem come in when you have the center ball that links the two u-joints together forcing them to always be at the same angle. This ball only allows a certain amount of angle so it now becomes the limitation of the joint. Ever see one of those 80 degree cv's??? The joint is much longer/wider/harder to manufacture...but they work slick.
     
  15. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Tom Wood's site has lot's of good tech info on this (www.4xshaft.com).

    Concerning the angle for CV (actually a "double-cardan" joint is the correct technical name) it states that a standard, non-modified, 1350 CV only allows 20 degrees and a 1310 only allows 30 degrees. I believe these numbers are comparable to a standard single u-joint setup if my memory is correct. Both CV's can be modified to allow more angle, but so can a regular u-joint yoke (grinding and clearancing).

    There is also a good write-up explaining why the pinion should point straight at the t-case output when using a double-cardan shaft.

    I'm kinda' of intrigued by the offset u-joint they now offer which allows about 10 degrees more angle in either the 1310 or 1350 series............
     
  16. four_by_ken

    four_by_ken 1/2 ton status

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    [ QUOTE ]
    Its amazing how many people don't know how a u-joint/drive shaft works /forums/images/graemlins/deal.gif


    [/ QUOTE ]

    EXCELLENT post. I am saving this information.
    /forums/images/graemlins/thumb.gif

    So, what about having normail u-joints at both ends... and having the pinion rotated up?
    I forgot the degrees, but mine is not directly at the output, slightly lower like you mentioned.
    Thanks again!
     
  17. four_by_ken

    four_by_ken 1/2 ton status

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    If I read correctly... having normal u-joints and having the pinion rotated... it will cause a vibration... since the lower joint will always have force...and the upper will only have force 1/2 the time when it is rotating?

    I think.
     
  18. four_by_ken

    four_by_ken 1/2 ton status

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    [ QUOTE ]
    I'm kinda' of intrigued by the offset u-joint they now offer which allows about 10 degrees more angle in either the 1310 or 1350 series............

    [/ QUOTE ]

    Who's the manufacturer?
     
  19. divorced

    divorced 3/4 ton status

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    [ QUOTE ]
    So, what about having normail u-joints at both ends... and having the pinion rotated up?
    I forgot the degrees, but mine is not directly at the output, slightly lower like you mentioned.

    [/ QUOTE ]

    The operating angles at both ends should be within a couple of degrees of each other.
     
  20. rcurrier44

    rcurrier44 1/2 ton status

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    The problem with that is if you have a normal u-joint at the upper end and a normal u-joint at the lower end; the first joint will have a changing velocity output because if its angle and the second joint will not have a changing velocity. Therefor the second joint will not be canceling out the first. In the wheeling world under slow RPMs this probubly would never cause a problem. But at highway speeds you will definatly feel a difference. You should -try- and keep the pinion shaft paralel with the output shaft of the tcase so the angles are the same at both the u-joints.

    In theory you could also tilt the pinion up far enough that the lower joint is at the same angle as the upper joint. Kinda like this /--\ ... creating a rainbow looking driveshaft falling from the tcase to the diff. This would put your pinion pointed above the centerline of the drive shaft but at the same angle as the upper joint...hope that made sence enough for people to understand. The problem with this would be getting enough oil to the pinion bearings because the pinion is pointed so high.

    EDIT: I have been thinking of adding a big oil slinger to my 14bolt and changing from a CV rear shaft to a regular shaft - setup in this mannor - when I change from a double t-case to a double transmission. You will also need an antiwrap bar because any axle wrap will put the pinion joint even farther out of alignment.

    Hey jess - how far would you say someone could tilt a pinion up before having oiling problems? I've seen some rear jeep driveshafts that looked realy high...
     

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