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Bad vibrations

Discussion in '40- & 55-Series Tech' started by bad_religion_au, Aug 19, 2003.

  1. bad_religion_au

    bad_religion_au

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    my 1976 Fj40 gets a bad vibration while driving under power (not occuring while rolling or on trailing throttle) and usually over 50KM per hour (so thats around 30Miles per hour or something)

    i have a suspision it could be drive shaft related... just a hunch.

    how do i tell if my universal joints on my rear drive shaft are in phase with one another? how would i line them up if i separated the two piece shaft?

    is it possible that the uni joints could have become out of phase???

    it may have something to do with last nights antics

    last night i was clowning around, playing with the fj, it was running sweet and i decided to climb a small concrete step up in 2wd, just to see if it would do it.

    the rear wheels spun for a second before hooking up and climbing the thing. it hooked up rather violently.
     
  2. roscoFJ73

    roscoFJ73

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    Check and see if you lost some of the balance weights off your drive shaft.Sometimes those antics you were doin last night can twist or bend a drive shaft also.There are drive shaft repair shops who will bench test (cheep) and repair if necessary . It could be in your uni joints take them off and see if there is any stiffness .
     
  3. bad_religion_au

    bad_religion_au

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    i didn't want to hear those "twist" or "bend" words too much :'(

    it looks like my universal joints are out of phase, and with the new vibration (i don't know if it was in phase to start with :-[
    ) so it could be that. a quick check showed that the shaft doesn't look bent, and couldn't see seams or cracks...

    lastly if i put up with the vibes, how long till i have a major problem.
     
  4. FJAfrica

    FJAfrica

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    Could just be the uni joint, usually the bottom goes, also gives a vibration at speed. Check for play in the joint.
     
  5. bad_religion_au

    bad_religion_au

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    would a bad uni joint cause the driveshaft to be out of phase?
     
  6. s79bj40

    s79bj40

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    yes and no. Not true out of phase, but out enough that it wouldn't be right. Its pretty easy to tell if the joints are bust when the driveshaft is out, difficult if it is still in. Fortunatly u-joints are easy to replace, if a bit too expensive

    it does sound like you twisted something though. I cant imagine that the u-joints would twist, they usually break. So def check the weights etc.

    sounds like your a bit of a trouble maker. Driving on the pavement ehh?

    sam
     
  7. s79bj40

    s79bj40

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    actually i cant see how it could be a bent driveshaft on reading it again, it would create the vibration during decelleration as well. When i first got my car the front driveshaft had the roller pins missing from one of the sides of one of the cups on the forward u-joint. I dont know how, they must have just fallen out at some time. I never noticed the vibration cause it was never used at speed, but there was heaps of driveshaft play, and i could see how that could cause a vibration on power but not neutral or decelleration. So it may be something like that. That or a bad bearing somewhere.

    Sam
     
  8. dinkleberry

    dinkleberry

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    If the vibe is only under power it's probably a bearing or a U.

    A bent or out of balance shaft would vibrate all the time.
     
  9. bad_religion_au

    bad_religion_au

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    more a friends front porch

    a different friend climbed the front steps of the melbourne exibition center (heaps of steps) ages ago, and i was talking to this friend about that, and i said that he recons it was one of the hardest climbs he's ever done, and i wasn't going to do it, but felt i needed to test this theory that stair crawling was hardcore, so i tried it on the steps out the front of this other friends house/garage shed thing.

    at the top of the stairs if you go straight there's a small drop off, so i drove off it. seeing there was no drama doing that, i tried to drive back up it (also because i forgot that behind the little concrete block is all fenced off with no gate.) so i had to drive it back over, where it left a fair rubber mark up his concrete, and then it kind of took off. didn't notice the vibe on the short drive back to university, but i didn't get over 50km/h

    sounds silly here, but at the time it was just like ramping up onto a rock. it's hard to explain the full setup he's got there
     
  10. bad_religion_au

    bad_religion_au

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    [quote author=dinkleberry link=board=1;threadid=4433;start=msg33137#msg33137 date=1061294085]
    If the vibe is only under power it's probably a bearing or a U.

    A bent or out of balance shaft would vibrate all the time.
    [/quote]

    bearing on the shaft? like in the U or more a bearing on the transfer case output shaft or something...


    should really change my sig line now eh? this is about the most stupid thing i'v ever done to my truck.

    on a side note, if i needed to drive it for parts, if i pull the rear shaft off, could i just unhook the rear shaft put it in 4wd hi, and lock the hubs and drive in under the front wheels? only about a 4 mile round trip.
     
  11. s79bj40

    s79bj40

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    all depends on how bad the vibrations are. Bearings in the line somewhere. Transfercase maybe, but i dont know, and those types of problems would only accumulate over time, not just appear. And i cant imagine they would cause a big vibration.

    Can you tell whether the vibration is bad, workes up to bad, or just appears at a certain speed. And can you feel it in the steering wheel or your arse?

    that should be a good indication.

    sam
     
  12. bad_religion_au

    bad_religion_au

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    how bad does a vibration get. it's felt more in the ass than the steering wheel, although there is some vibration through the steering wheel. like i said, coasting or under trailing throttle, it is normal, under acceleration there is a slight seat felt vibe, building to a little rattle in the steering wheel

    ohh and it doesn't occur untill i accelerate over about 50 km/h
     
  13. s79bj40

    s79bj40

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    def check the driveshaft, but also mounts for all things movable, body, g/box, t/case, exhaust, etc. Torque from accell could cause any of them to move enough on a bent/broken mount to tap the body/frame without being audible. Other than that, it cant really be anything that remains constant over velocity change. like the wheels gearing. But its so difficult to tell without having a closer look.

    sam
     
  14. bad_religion_au

    bad_religion_au

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    thanks, i guess i'll have to have a poke around after the sun comes up. it vibrates real quick. the driveshaft did look out of phase...

    the 2 piece shaft, where it pulls apart, does that have gears/ teeth that could have jumped out or moved around while rotating and settled into a different place, puting the shaft out of phase?

    check for play by rattling it around, up and down, left and right?

    if i have play, i should drop it out, order new joints, or whatever is busted? or is there a repair?

    interesting side note, when i got under there today and had a poke around, my driveshaft doesn't angle down, like most 4x4 shafts, the amount of sag in the rear of my fj means the shaft has to travel upwards from the trans case to the diff. that's how low my rear springs have sagged.
     
  15. s79bj40

    s79bj40

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    it does have teeth from what i can remember, but it is extremely unlikely that it pulled apart and pushed back together again without the two bits droping on the ground. How does it look out of phase? The two u-joints look aligned on my car - like with the ends of the u-joint cups lining up with each other.

    when you are driving at faster speeds with no hands, can you see the steering wheel move much?

    anyway I dunno damnit. One of the yanks is sure to know when they get on though.

    sam
     
  16. bad_religion_au

    bad_religion_au

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    thanks heaps man, i'll test drive it later,

    it looks out of phase because it looks like the two u joints are out of alignment, like one points at the ground, the other about 20 degrees out...
     
  17. theo

    theo

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    [quote author=bad_religion_au link=board=1;threadid=4433;start=msg33161#msg33161 date=1061298459]
    thanks heaps man, i'll test drive it later,

    it looks out of phase because it looks like the two u joints are out of alignment, like one points at the ground, the other about 20 degrees out...
    [/quote]

    Yep, that's out of phase. Unbolt one end, pull the slip yoke apart, and put it back together with the u-joints aligned. But it could not have happened while driving.
    ::) :)
     
  18. bad_religion_au

    bad_religion_au

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    well the vibe occured after the mentioned incident, and i haven't had my driveshaft off, let alone appart in the year i've owned it, so i guess that it's not the new source of te vibration then :-[
     
  19. theo

    theo

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    These are your own words. You were speculating that the u-joints somehow magically went out of phase because you climbed some stairs. I never assumed or implied you took the shaft apart. I'm just saying it isn't likely they went out of phase while driving. How can slip yoke splines do that? A twisted shaft is much more plausible.

    The vibration that just started is from something else. But if your u-joints are 20 degrees different, they're out of phase. Maybe if you fixed that, you would find some other problem while you're under there.
     
  20. bad_religion_au

    bad_religion_au

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    ok, so i checked my uni joints in the light. no slop what so ever, the uni's are out of phase, and i didn't think they could go like that without pulling them apart, so i'll assume they been like that since the PO. i havn't got a chance to tear into the prob, just check for slop in the uni's.

    i still cannot see any evidence of a cracked or twisted shaft, but i am no expert.

    when testing the uni's i also wiggled the trans and transfer case, which seemed solid, although the first time i tried to move them there was a slight bump, but was silent after that.

    i'm stumped and have no time for this at the moment. thanks for the suggestions though.