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how to check rear end ratio??????

Discussion in 'The Hokey Ass Message Board' started by Stovebolt, Mar 4, 2004.

  1. Stovebolt
    Joined: May 2, 2001
    Posts: 3,530

    Stovebolt
    Member

    I know this has been discussed before, but Im stuck, and need the answer quickly.

    If I rotate the right axle around once and the tailshaft yolk turns twice, then what ratio do I have???

    Is there a formula to work the rear end ratio out by this method??? [​IMG]

    Thankx in anticipation.

    cheers
     
  2. Paul2748
    Joined: Jan 8, 2003
    Posts: 2,375

    Paul2748
    Member

    You probably have a 2.50 - 2.75 ratio. Hard to believe a 2.00. Check closer on how may times the yoke turns. Probably turns a little more than 2 times.
     
  3. Stovebolt
    Joined: May 2, 2001
    Posts: 3,530

    Stovebolt
    Member

    The bloody thing has a 3.55 tag on it and I just want to make sure it is 3.55 before I take it down to get one side narrowed. Its a borg warner - so I can't just pop the centre.

    I've tried it twice and get 2 rotations for each axle rotation.
     
  4. Patina
    Joined: Jul 21, 2003
    Posts: 20

    Patina
    Member

    When i check my 62 chev i had to turn both wheels at the same speed to get a accurite reading, turn out to be 308s PATINA
     

  5. Munson
    Joined: Dec 27, 2003
    Posts: 198

    Munson
    Member
    from Tempe, AZ

    what vehicle, any numbers on it?

    My '59 apache had 3 tags, ( 3.92, stamping id#, and use only limited slip fluid.... warning tag)

    If its an old truck like mine you can look it up on their site http://www.americanclassic.com/

    good luck!
    j
     
  6. burger
    Joined: Sep 19, 2002
    Posts: 2,371

    burger
    Member


    You know, I tried the spinning method not too long ago on two different rear ends, and got nonsense. The one rear was known to be a 3:55, but I was getting 20 turns at the drum for 14 at the yoke, which seems like a 7:1 ratio. I tried the same thing on another rear I had lying around and got the same double figure. Can anyone explain that?

    Ed

    PS- Both rears were peg-leggers, if that makes a difference.
     
  7. Stovebolt
    Joined: May 2, 2001
    Posts: 3,530

    Stovebolt
    Member

    I realize now that I was spinning the right axle and the left was jammed up hard against something else.

    I rotated the yolk and got 3 turns to 1 on the axle - so it still doesn't add up to a 3.55 ratio.

    am I wrong or is it a 2.92 or something?
     
  8. skipperman
    Joined: Dec 24, 2002
    Posts: 1,837

    skipperman
    Member

    This ain't gonna make sense with the numbers you gave--BUT--- the way to check a rear ratio is ....
    If it's an open rear (NON posi)---Mark the driveshaft with chalk.... HOLD one wheel still...turn other wheel TWO REVOLUTIONS and count how many turns the chalk made ...
    If it's a posi ....(don't hold either wheel) turm wheel ONE revolution and count how many turns the chalk made ....... That's it bro ......


    jersey Skip
     
  9. draggin'GTO
    Joined: Jul 7, 2003
    Posts: 1,792

    draggin'GTO
    Member

    For an open (non-posi) rear leave one tire on the ground and turn the driveshaft (mark it) until the other tire (mark it too) that is off the ground rotates exactly TWO times. The reason for the two tire rotations is because the spider gears are a 2:1 ratio. The number of turns of the driveshaft will be your gear ratio.

    For a posi rear (working properly) get both tires off the ground and turn the driveshaft until the tire(s) rotate exactly ONE turn.

    This method works every time. [​IMG]
     
  10. burger
    Joined: Sep 19, 2002
    Posts: 2,371

    burger
    Member


    I see the error in my ways. Many tanks.


    Ed
     
  11. Stovebolt
    Joined: May 2, 2001
    Posts: 3,530

    Stovebolt
    Member

    I am much obliged to you all.

    I hope this helps out others that have the same lack of knowledge in all things mechanical as I have.

    Again "THE HAMB RULES"!!!
     
  12. Stovebolt
    Joined: May 2, 2001
    Posts: 3,530

    Stovebolt
    Member

    Thanks guys. I tried it and yes I do have a 3.55 ratio rear end.

    So now its off to get narrowed, and set up with '36 radius rods, and an A model spring.

    Cheers
     
  13. atch
    Joined: Sep 3, 2002
    Posts: 5,620

    atch
    Member

    just a quick finishing note: to increase accuracy, rotate the rear wheel 20 times instead of two; ten if positrac. obviously divide the yoke rotations by 10; then divide to get the ratio.
     

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