OK, so I'm an idiot redux

Discussion in '80-Series Tech' started by IdahoDoug, Jun 14, 2005.

  1. IdahoDoug

    IdahoDoug

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    Last summer or fall, I pulled my rear driveshaft to lube the splines on the 93. Put new tires on a while later and have been unhappy at a freeway vibration the tire shop doesn't seem to be able to get rid of that I attributed to the tires.

    Yesterday, I repacked the wheel bearings on the other 80, and lubed both truck's shafts while I was into the grease. Whups, what's this? On the 93 the rear shaft grease fittings don't line up. Unbelievable - I put the rear shaft section on 90 degrees out of phase! Fixed it, and most of the vibration is now gone.

    So, to anyone who's got an unexplained freeway vibration, consider being sure that your rear drive shaft is properly installed IN phase (ears on the shaft portion in line with each other at each end), and that the front shaft is properly installed OUT of phase (ears at each end 90 degrees to each other). Your grease fittings should be very close to a perfect straight line.

    I'm such a bozo sometimes....

    DougM
     
  2. lowenbrau

    lowenbrau

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    This seems odd. Can anybody explain why the front shaft should be out of phase? That's gotta suck on a lifted truck.
     
  3. IdahoDoug

    IdahoDoug

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    Being in or out of phase is a decision the mfr makes based on the expected running angles, length of the shaft, shaft weight, and other variables that cause or cancel vibrations. During testing, Toyota must have found that this combination caused the most ideal level of smoothness for the 80's running gear. The out of phase shaft is indeed unique AFAIK, and why I'm suggesting anyone who's acquired their truck used check this out due to unknown previous maintenance.

    DougM
     
  4. elum

    elum

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    "Idiot?" Real idiots don't drive Cruisers!
     
  5. e9999

    e9999 You want to do what...? Moderator

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    well, errr...., OK..., and...? :D

    (NTTIAWWT :D )
     
  6. TX_TLC

    TX_TLC

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  7. T Y L E R

    T Y L E R

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    Well this is just great! I now have two choices ...


    1 ) Forget I ever read this thread ... or

    2 ) Begin cutting a few inches off the legs of the pedestal I've had you on. ;)



    :crybaby:



    TY
     
  8. IdahoDoug

    IdahoDoug

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    Not the PEDESTAL - NNNNNOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!
     
  9. T Y L E R

    T Y L E R

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    Ok , ok .... I'll just have to pretend that I never even viewed this thread TWICE :D


    Consider it done ..



    :beer:
     
  10. scottm

    scottm

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    U-joints don't transfer rotation smoothly, the out-going end speeds up and slows down twice every revolution. It's worse as the angle of the joint increases. If you have u-joints in your socket set you can try spinning them at different angles. A second u-joint after the first can make the problem worse, or cancel it out. When the first joint is speeding up it's output, the second joint (on that sped-up shaft) can slow it's output if it's out of phase. So the output of the second joint ends up the same speed as the input of the first joint. If they're in phase the output shaft is twice as fast/slow as the middle shaft. Got a headache yet?

    Normally to be approximately out of phase, the joints are at 90-degrees to each other, and the angles of each are about the same and in the same plane. The joints each have an input yoke and output yoke, looking at them you can see the input yokes are 90-degrees to each other.

    On the 80s front driveshaft, the two joint's angles aren't in the same plane. To get the joints to cancel each other they need to out of phase relative to their individual angle planes, which they are, roughly. Lifting the truck changes these angle planes, so the joints would have to be rotated to stay out of phase.
     
  11. IdahoDoug

    IdahoDoug

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    Thanks - forgot about the front shaft's two joints having different angles. Also, return of your rear bearing tool just got delayed a week as I got nervous about the 93, and Mark-Erik's untouched 280,000 mile rear bearings have also piqued my interest. We ordered two gasket sets today from Cdan to repack both of them. I've got it down to about 3 hours if the drums come off reasonably.

    DougM
     
  12. lowenbrau

    lowenbrau

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    scottm, thanks for the explaination. This makes more sence.
     
  13. scottm

    scottm

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    No hurry, Doug. The more practice you have, the faster it'll go when you come do mine!
     
  14. semlin

    semlin discouraged user

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    scott

    do you mean that the relative angle of the u-joint arms should vary from 90 degrees according to the height disparity between the t-case and diff output? If so, can the needed change in angle be calculated and the u-joints arms rotated on the drive shaft splines to suit? Could this reduce vibrations on lifted trucks?
     
  15. scottm

    scottm

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    Each u-joint has two yokes, linked by a spider and bearings. Looking at the u-joint, you should be able to eyeball the plane formed by the input and output shafts. If the first joint has it's input yoke straight across it's plane, the second should have it's input yoke flat to it's plane. That's perfectly (90-degrees) out of phase. If each u-joint is bent at the same angle, they will perfectly cancel each other's vibrations. If they're not at the same angles, they'll still cancel each other to some degree if they're out of phase.
     
  16. semlin

    semlin discouraged user

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    thanks scott. i think i might finally understand driveshaft lift/caster vibration issues thanks to that explanation. so if i understand you, because the angle of the axle output plate is different from the angle of the transfer case output plate, the u-joints are rotating at different angles and thus the rate of speeding up and slowing down of each u-jointdruing a rotation is different. The 90 degrees oppositional phasing does not perfectly offset because of this difference, but is close enough at stock?

    so when you increase the lift of the truck (assuming no change in caster) you increase the angle of the drive shaft which increases the relative speeding and slowing of both u-joints equally during each rotation. The fact the acceleration and decelleration is happening faster increases the degree of disharmony that the out of phasing can't compensate for?

    if you don't compensate for the negative caster caused by lifting without lengthening the leading arms you change the angle differential of the axle plate relative to the transfer case. It would seem that this negative caster would make the angle difference greater if I assume the transfer case output plate is more or less vertical.

    This would mean that a positive increase in caster overstock would decrease the angle differential and offset driveshaft disharmony from a bigger lift. i know that has other impacts on handling but it would potentially reduce vibration. is that right?

    sorry to belabour this but when a light bulb goes off in my head i like to capture it.

    hows the healing up going by the way?
     
  17. scottm

    scottm

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    I haven't looked to much at caster, I just have some experience with u-joint design. Lifting the truck rotates the axle housings a bit. They are on those long swingarms to minimize that, but you'll need to modify something to get them back to level with the lift. That will keep the angles about equal on the pairs of u-joints on each driveshaft.

    The front driveshaft has angle planes kind of 45-degrees to horizontal. Lifting moves them more vertical, rotating them in opposite directions. It might help to rotate the yokes to keep them close to out of phase, maybe just one spline. Mr. T had the benefit of 3D CAD when designing all this, I'm sure they're perfectly out of phase when stock.

    Healing well, thanks. Riding, lifting, no running or long walks yet. No flying, I really want to be 100% for that, as do my passengers and co-workers I'm sure.
     
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