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Driveshaft length

Discussion in 'Engines and Drivelines' started by Snicklefritz, Apr 10, 2022.

  1. Snicklefritz

    Snicklefritz
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    For a car with a buggy (transverse) leaf spring, and hairpin radius rods, I wonder what the minimum advisable driveshaft length might be. I'm new to this car-building stuff, so I don't know how much travel such a rear suspension might have, but I've seen some 'buckets with very short wheelbases.

    bobtail with radius rods.jpg
     
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  2. old round fart

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    We get very little bounce in buckets. I think you would be safe with about 2” from all the way in.
     
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  3. T-Test

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    Drive shaft-+8" or whatever is needed
    1/2' to 2" yoke to tailshaft depending on how long the yoke is.
    No more than 2" offset from tailshaft to pinion.
     
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  4. Snicklefritz

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    how would that correspond to driveshaft legnth? i take it that with an about 2 inch (shaft?) travel the suspension doesn't move all that much.
     
  5. Snicklefritz

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    you mean 1/2 inch to 2 inch? and could you clarify what you mean by 8" or whatever is needed? not sure i get it.
     
  6. Neshkoro

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    That was my question, too!
     
  7. 409T

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    I think of it as if the drive shaft were already installed and I unscrewed the U-bolts at the differential, the drive shaft could be pushed forward 1" before it bottomed out in the transmission.
     
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  8. Neshkoro

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    I’ve experienced a driveshaft that wasn’t engaged enough to the tail shaft One big dip and a bump and the drive shaft came out far enough of the trans to do some real damage. Not a pretty sight!! Something bending and coming out of balance at 60 mph is enough to scare the crap out of you.
     
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  9. Snicklefritz

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    so no thoughts about minimum length of the driveshaft it self?
     
  10. Spanky

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    There's really no minimum. I've heard of some short wheelbase cars that bolt the tranny tailshaft directly to the diff. with a u-joint!
     
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  11. Neshkoro

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    I would think if you bottom out the yoke, pull it out an inch and use that dimension for the driveshaft length you should be ok. Although, you don’t want to bottom out the yoke on a bump either.
    Anyone have thoughts?
     
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  12. old round fart

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    My original car drive shaft was 5” long. The yoke for the turbo 350 was longer than the shaft.
     
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  13. Neshkoro

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    That’s where I’m hung up. If the trans is mounted and the rear end is mounted where you want it, that’s what is going to dictate the drive shaft length. Install the yoke all the way in, pull it some amount around 1” and measure between the front and the rear u joint. That’s the drive shaft length. Easy peasy.
     
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  14. Snicklefritz

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    at this point the drivetrain (heck, everything) is in early mock-up. it's gonna be a shortwheelbase car so space is tight i think; maybe not as bad as i may suspect anyway. i think my concern arose when looking at how things rest, not many final fixed points yet, and seeing the distance from the end of the transmission to the rearend looks mighty tight. i didn't bother with a measurement but maybe it's about five inches?

    as you all have touched on the things to think about how much room the yolk has to move and suspension travel.
     
  15. T-Test

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    You will be an Automotive Engineer when you get through with the car, I garan' T you that.

    Or you'll sell it from the headache before it's done.:whistling:
     
  16. Neshkoro

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    I hate this expression but “it is what it is”. Whatever it takes to connect those two things together , “it is what it is”!Go for it.
     
  17. 409T

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    A drive shaft that is only 10" long overall will only move in and out of the transmission 3/16" (actually .2") on a 2" vertical movement of the rear end. A 1" vertical movement would result in just under 1/16" lateral travel. The rear ends "usually" travel up and down less than 2" so I would say you are on the right track, your mileage may vary.
     
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  18. Snicklefritz

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    man that's a bit less travel than i would have guessed. gives me some perspective for sure.
     
  19. Spanky

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    (duplicate post :unsure:)
     
  20. Spanky

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    I'll say this . . . my driveshaft was one of the last things I did in my build. By the time you need yours, all the components involved will be in their "fixed" positions.
     
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