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Drive shaft angle...how much is too much?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by jekbrown, May 30, 2001.

  1. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    I am still trying to track down that vibration noise on my '85 Jimmy...I ave 4" of suspension lift and an inch of body lift...was wondering how much drive-shaft angel a slightly-lengthened but factory driveshaft can handle. Isn't it only like 20 degrees?

    J
     
  2. HarryH3

    HarryH3 1 ton status Author

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    Driveline vibrations are caused by the difference between the operating angles of the u-joints on a driveshaft. Many lift kits tilt the rear pinion upwards, to lessen the operating angle on the rear u-joint. But this makes it different than the angle on the front u-joint, up at the transfer case. This difference makes the driveshaft get slightly longer and shorter with each revolution. It's just a small amount, but it's enough that you can feel the vibration. Match up the angles of the u-joints and the vibration will go away.

    Take a look and you'll probably find that the rear u-joint has a very small operating angle, while the front one has a much higher operating angle. The 2 angles need to be within 1-2 degrees to minimize any vibrations.

    BTW, Spicer recommends a maximum operating angle of 7 degrees for their standard u-joints. [​IMG] Beyond that, the life of the u-joint drops as the angle increases. Jesse, over at <A target="_blank" HREF=http://www.highangledriveline.com>http://www.highangledriveline.com</A> can make you a custom CV-style driveshaft that will operate at 80 degrees. [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
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  3. CaptCrunch

    CaptCrunch 1/2 ton status

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    Is this in 2wd or 4 wd drive.... what degree shims are you using in the front and rear? If it is a rear one (in 2wd) then have you dropped the t-case? Do you have rear springs 4", shakle flip? blocks? If it only happens in 4wd it is probably the frt shaft... first check for binding and you could possibnly have to grind on the CV joint a little.... otherwise what degree shims are in there?

    -Mikey
    1987 Chevy K5 Blazer- 350 TBI
    <A target="_blank" HREF=http://www.geocities.com/milnerlives_2000/blazer.htm>http://www.geocities.com/milnerlives_2000/blazer.htm</A>
     
  4. 1990K5

    1990K5 1/2 ton status

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    re:dr shaft angle issue

    dont mean to discourage, but w/a 4in lift or higher and a slip yoke most likely you will have angle issues no matter what you do, having both ends at the same angle will help but it won go away, i have done every thing under the moon to combat this problem on my k5, shimmed up/dn, lenghtened/shortened shaft, rebuilt rear end, rebuilt t- case, shacke flip, traction bars, you name it, ive done it! and still when i let off the gas at 40mph or above the damn thing sounds like its going to come apart. just went from 4in blocks to a 6-7in shackle flip (which i was sure would cure any axle wrap) did not change a thing, the only other option i have is too swap my 241's output shaft for a ford one
     
  5. yeild2me

    yeild2me 1/2 ton status

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    Re: re:dr shaft angle issue

    this is a sore subject here at my shop....i have a 4"shackle flip, 14 ff, dropped my t-case and currently have my pinion shimmed 4 degrees down, helped but still sounds like its going to come apart when i let off, now that my hard top is permantly off along with my rear gate, the rear is even higher now, so i am going to take one last stap with a 6degree shim and drop my t-case a little more,and if that doesnt fix it, i am going to get a CV shaft. w/o any shims or anything, my rear pinion points directly towards the t-case, so i am guessing a CV will be the ticket....


    one last note-it comes on at about 35 and gets really bad by 55, then sorta evens out or maybe even decreases above 65. this is like normal acceleration on the hi-way---does this sound the same as you guys??
    AIRBORNE!!<P ID="edit"><FONT SIZE=-1>Edited by yeild2me on 05/30/01 09:15 PM (server time).</FONT></P>
     
  6. drivelineman

    drivelineman 1/2 ton status

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    Re: re:dr shaft angle issue

    we are working on the part#'s for a fixed yoke 208 kit now- were close -this wold be nice for all you 208 case users-
     
  7. yeild2me

    yeild2me 1/2 ton status

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    Re: re:dr shaft angle issue

    hey jesse, i have a 241- same thing?? i will probably be getting one....these are not "good vibrations"

    AIRBORNE!!
     
  8. HarryH3

    HarryH3 1 ton status Author

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    Re: re:dr shaft angle issue

    yield2me, a worn or loose slip yoke will also cause that symptom. I had that problem on a brand new '79 F-150 many years ago. Back off the throttle on the highway and you could feel the whole truck shudder. They replaced the axle bearings, ring and pinion, and the posi-trac (under warranty!) before finally deciding to swap out the driveshaft itself. The problem was solved at last. [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
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  9. yeild2me

    yeild2me 1/2 ton status

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    Re: re:dr shaft angle issue

    hmmmmm, i should look into that....i have had the d-shaft replaced -so that aint (read- shouldnt) be it, and i do have a problem with the t-case seal, AND it does have 160000miles on it, AND it is the only piece i havent messed with.

    thanks H3, gives 1 more avenue of approach

    AIRBORNE!!
     
  10. MuleMaster

    MuleMaster 1/2 ton status

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    Re: re:dr shaft angle issue

    I experienced really bad vibrations at the very same speed too after my 4" lift. Last week I dropped my tranny (pic soon on my website) and the success was unbeliveable: The vibrations disappeared nearly complete, only minor ones left which I blame on the 23 years of age of the truck.

    <font color=blue>K5 Blazer...because size DOES matter
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