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vibration sensation?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by foxman, May 15, 2002.

  1. foxman

    foxman 1/2 ton status

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    what is axle wrap? does this cause you to eat up u joints. this is the third one I've had to install. how much does it cost to have my (1 piece) drive shaft ballanced? Is it common for them to become out of ballance? Especially when your u-joint falls appart and your axle develops a lot of slop in the rear joint as a result? This is the rear driveshaft I'm talking about.
    about every 2 months it (the rear u-joint) starts chirping and vibrating like crazy untill I replace it. When I pull the old one out it feels like it's bound up some how, almost impossible to move.
     
  2. foxman

    foxman 1/2 ton status

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    anybody help me with this one?
     
  3. Goober

    Goober 1/2 ton status

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    Axle wrap is the twisting of your axle housing under heavy acceleration. To help visualize it, think about what happens to the rear axle when you stomp on the gas at a stoplight. The pinion gear (connected to your drive shaft) cranks on the ring gear which makes your axle shafts (connected to your wheels) turn forward.

    If you have ever taken a physics class, one of the more interesting characters you will study is Sir Isaac Newton. He did lots of cool stuff related to objects in motion and even wrote some guides (laws) describing how things move. Newton’s third law of motion is the one that applies to axle wrap.

    Newton's third law of motion says:
    "For every action, there is an equal but opposite reaction"

    As your axle shaft spins the wheels in one direction, it has to push against the axle housing in the opposite direction. That force tries to twist (or WRAP) the axle housing in the opposite direction. Have you have ever seen a hot rod with those funny looking bars under the front part of their rear springs? Those are traction bars designed to control axle wrap.

    A well designed 4X4 suspension will hold the axle housing in place with the spring pack and prevent it from twisting. But if somebody decides that they want to put 8" lift blocks on their rear axle with 600hp under the hood they will get a rude introduction to severe axle wrap.

    With your rear U-joint right next to the end of your pinion gear, excessive axle wrap will tend to make the u-joint work at extreme angles which will reduce its life significantly. Bent and out-of-balance driveshafts will also burn through u-joints.

    OK, Class over. /forums/images/icons/smile.gif



    If this was my truck, here is what I would do:

    First , I would check my driveline angles. A driveshaft with 2 u-joints (1 in front and 1 in the rear) will need to have a 2 - 6 degree angle at each joint. Both of the ends should be within 1 degee of each other.

    Next, I would verify that my drive shaft was straight and balanced. If you don't have the equipment then take the shaft to a reputable driveline shop and have them check it out for you. They will probably put in new u-joints and put it on their balancer. It will cost a few $$ but it's worth it.

    Finally, I would check my pinion bearings before putting the driveshaft back on. It may also be a good idea to change the differential oil and check out all of the gears for signs of excessive wear or breakage.

    After going through all that, you shouldn't have any more u-joint problems.

    Have fun! /forums/images/icons/cool.gif
     
  4. COLLISION

    COLLISION 1/2 ton status

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    EVALUATING DRIVELINE VIBRATION
    (DIAGNOSIS FAULT TREE) #89-T-73

    MODEL: 1980-89 LIGHT DUTY TRUCKS

    The purpose of this bulletin is to provide a logical approach to evaluating vehicles tor driveline generated vibrations and
    imbalance occurring between 5O-62mph. The following diagnosis tree is designed to be used as a guide, and when utilized
    properly can help isolate and identify causes of driveline disturbances.

    PROCEDURE

    Prior to road test, determine if disturbance is engine related by following the procedure below:

    1. With engine at operating temperature and vehicle parked, set parking brake and place transmission shift lever in neutral.

    2. Slowly accelerate engine from idle to 4000 RPM (diesels 3200 RPM), noting RPM at which vibration is felt (if any).

    3. If vibration is felt, disregard use of this bulletin and isolate and repair responsible engine component (transmission,
    clutch/flywheel, torque converter, engine accessory, etc.).

    Road test vehicle on a smooth level road to verify customer comment. It is usually beneficial to road test the vehicle with the
    customer present. Note the speeds and conditions at which the disturbance is most noticeable. Refer to Remark A in this
    bulletin for diagnosis information.

    TO USE DIAGNOSIS TREE:

    Locate symptom on the diagnosis tree which best describes the disturbance. Follow arrows and perform the required check
    or service action. Never bypass or skip an inspection or assume that a component is OK. All steps must be performed as
    called out.

    DEFINITION OF TERMS

    "Boom" - Continuous bass drum roll sound caused by body cavity resonance excited by drivetrain. Sometimes felt as
    pressure in ears.

    "Buffeting" -High pressure pulsation.

    "Droning" - A low heavy reverberating often muffled sound. Sounds like a bowling ball rolling down alley.

    "Drumming" - A drum roll similar to "Boom."

    "Howling" - A mid-range continuous sound usually associated with driveline gear noise.

    PROCEDURE

    1. Measure run out of companion flange, as described in Figure 2. Indicate high point with a mark.

    2. Remove companion flange as described in Section 4B of the Service Manual.

    3. Measure run out of pinion stem at radius between nut thread and spline. Mark low point.

    4. Reinstall pinion companion flange with marks aligned. Tighten pinion nut to specification torque. Refer to Section 4B of the
    Service Manual.

    5. Remeasure companion flange runout. If excessive runout still exists, do Step 6.

    6. Additional reindexing of the companion flange to the pinion stem splines by one or two teeth may further reduce runout.

    REMARKS

    A. Verify concern. Drive on smooth road up to 65 mph as speed limits permit. Note speeds and severity of disturbance.
    Assure that disturbance is not engine or transmission related. Refer to Section OC "Vibration Diagnosis Chart" in the 1989
    Service Manual. If disturbance is determined to be engine/transmission related, disregard use of this bulletin.

    B. Disturbance may peak within this speed range.

    C. Visually check components for damage, looseness, missing balance weights, etc.

    D. This may compensate for companion flange run out.

    E. Excessive companion flange runout may occur as high prop runout. Replace companion flange as required, see Figure 2.

    F. IMPORTANT: If runout is reduced to below 0.005-inch and the flange possesses a compensation weight, this part is out
    of spec. See Figure 2.

    G. Ensure the companion flange run out is still well within specifications.

    H. If this point has been crossed several times, it is recommended that the Technical Assistance Center be contacted.

    I had the same problem with mine, I fixed u-joint angles and it's much better, but still there at hwy speeds only under load
     
  5. foxman

    foxman 1/2 ton status

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    Thanks for all the insight I might have a little trouble finding the angles of the shaft at each joint but right now they look pretty different. can it be eyeballed? what might you suggest for an angle finder? thanks agian for all the help.
    Jeremy
     
  6. Goober

    Goober 1/2 ton status

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    Well ... the coolest angle finder I have ever seen was at a Dana driveline school. It had a digital readout and magnetic base. very cool and very $$$$$$$$.

    Just head down to your local hardware store (Ace, Lowes, Home Depot etc.). They should be able to help you out.
     
  7. dogman

    dogman 1/2 ton status

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    just a suggestion:
    make sure the caps of u-joints are inline with the u-joint caps on the other end of the drive shaft.
    also: if your driveshaft is bent, just enough to change the balance; you will dust your u-joints.<if your driveshaft came off and banged around, it maybe bent. <mine was.
    also: check your yokes, if the tabs that keep the u-joint centered and if they are worn or missing; you will need a yoke. <mine was
    if your thinking of a re-balance on it, put your money into a New drive shaft. <been there, re-balanced one and still lost U-Joints. When I replaced the driveshaft, I got rid of my vibration and u-joint dusting problem.

    77' K10 350, 4sp <I ordered it new.
    good luck.
    Thomas
     

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