Figuring out rear axle ratio...what the......

Transmissions and Rear Ends

  1. shadango

    shadango Well-Known Member

    Messages:
    408
    Likes Received:
    37
    Joined:
    May 30, 2016
    Location:
    Pittsburgh, PA
    So on my Cuda, when I got it, I wanted to know what the rear axle ratio was.....I marked the rear wheel on the inside surface and a corresponding mark on the backing plate.....then a mark on the shaft yoke and a corresponding mark on the lump.

    Rotated the wheel one turn and counted the number of turns of the shaft. Got around 2 3/4, which is a 2.76. When I pulled the 3rde member later I confirmed that....2.76.

    Well, tried the same thing on the Volare the other day...and got 1.3 turns....that would be 1.33:1.....cant be right, right?

    I had to do something wrong...the lowest rear gear was 2.00 or something like that right?

    I looked on youtube and there are folks who did it like me and then guys who do 10 full turns of the wheel and divide by 10......

    I tried both letting the other wheel rotate opposite (its a peg leg diff) and also tried blocking one wheel.

    I tried having it in neutral and in drive....get the same.

    What....the.......heck........??
     
    BudW likes this.
  2. MiradaMegacab

    MiradaMegacab Well-Known Member

    Messages:
    1,586
    Likes Received:
    399
    Joined:
    Feb 27, 2011
    Location:
    Long Island NY
    Open diff, spin the wheel two revolutions and count how many times the driveshaft turns.
     
    shadango likes this.
  3. shadango

    shadango Well-Known Member

    Messages:
    408
    Likes Received:
    37
    Joined:
    May 30, 2016
    Location:
    Pittsburgh, PA
    ......but wouldnt TWO wheel revolutions throw the math off if I am looking for a "X:1" number?
     
  4. MiradaMegacab

    MiradaMegacab Well-Known Member

    Messages:
    1,586
    Likes Received:
    399
    Joined:
    Feb 27, 2011
    Location:
    Long Island NY
    With one wheel up and the other on the ground, the above method is the way to check an open diff. I'm guessing you have a 2.76
     
    shadango likes this.
  5. BudW

    BudW Moderator Staff Member

    Messages:
    4,194
    Likes Received:
    1090
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    An open differential (which by far most are) - you have to either spin both rear tires at same time (easier said than done) OR block one from spinning – or you will get funky numbers.

    If you block one wheel, then you have to double the tire revolutions for math to be correct.


    I have gotten to the point it is easier to just remove the cover – for it generally is way past due to have lube changed anyway.
    BudW
     
    shadango likes this.
  6. shadango

    shadango Well-Known Member

    Messages:
    408
    Likes Received:
    37
    Joined:
    May 30, 2016
    Location:
    Pittsburgh, PA
    Yeah I was thinking along those lines myself.....I guess I forgot about the TWO revolutions....duh.

    Guess we'll have to take another shot next time her butts up in the air (the car).
     
  7. shadango

    shadango Well-Known Member

    Messages:
    408
    Likes Received:
    37
    Joined:
    May 30, 2016
    Location:
    Pittsburgh, PA
    Well, when we first got the car we just suctioned the old lube out (it was actually not bad looking at all) because we were short on time and to be truthful I HATE trying to clean and seal the diff covers...LOL. My cuda has the 8 3/4 so drain and fill plugs....easy peasey.

    I guess at some point we SHOULD pull the cover to look in there, but so far the diff sounds good etc and I hate to hex it by saying that.

    Also been debating on whether to drop the tranny pan.....ya know how they say if the trams has not been changed regularly, and you do, then you are asking for issues....then again I guess NOT doing anything is asking for trouble too...LOL. I have a tranny shop I trust and I may just drop it off and say "drop the pan, check it out and see what you think".....its only money I guess....LOL <sigh>
     
  8. BudW

    BudW Moderator Staff Member

    Messages:
    4,194
    Likes Received:
    1090
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    I understand the concept of
    But I don’t actually see it in real life.

    Most cases, you are good to go.

    The transmissions that look terrible (fluid, debris in oil, etc.) then you might have caught the problem before it got any worse.

    Transmission soft parts (clutch disks, bands, bearings) wear no matter what.
    Transmission hard parts (gears, drums, shafts, etc.) do not wear normally – unless lack of fluid (leak, stopped up filter, etc.) or ran with a lot of metal in the pan.

    Generally, when pan is dropped and a stopped up filter is seen or a lot of metal is in pan (some metal flakes are normal – but not teaspoons worth) or an excessive amount of fiber in in pan (some fiber is normal), then you are fine.

    If excessive amount of metal or fiber is present then most shops will advise you of this before going back together.
    Personally, I think in those cases, you have extended the transmission life, not shortened it any. With that said, I have no proof either way (an unprovable condition).

    I have another personal belief that transmission fluid – no matter who makes it or what is hyped about it – is only good for about 30k miles, especially in our older cars.

    The people who do change fluid every 30k miles – I rarely ever see any transmission problems with, except for things like leaking gaskets or solenoids (which fluid wouldn’t have any effect on).

    Transmission fluid only has a certain lifespan and about 30k miles is about it.
    If you drive like I do, or use car to tow with, then every 15k miles may be closer to what is needed.
    BudW
     
  9. BudW

    BudW Moderator Staff Member

    Messages:
    4,194
    Likes Received:
    1090
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    Differentials doesn’t have the same issues automatic transmissions have.

    You can tell when differential fluid has turned. It won’t be opaque and it smells bad.

    If there is any metal in it, then try to get all metal out when fluid is changed.
    Fluid should be changed again soon, to get all traces of metal, out.

    Metal and fluid leaks (and water) is what kills differentials.
    Well, maybe maniac drivers like me . . .
    BudW
     
  10. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,108
    Likes Received:
    242
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    Peg-legging doesn't to them any good either.
     
  11. shadango

    shadango Well-Known Member

    Messages:
    408
    Likes Received:
    37
    Joined:
    May 30, 2016
    Location:
    Pittsburgh, PA
    Finally got back to this...yep, its a 2.76. Thanks all for the help!
     
    MiradaMegacab likes this.
  12. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,108
    Likes Received:
    242
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    Well, if nobody wants to say thank-you, I will, but more so goodonya, and keep the problems coming,lol
     
  13. shadango

    shadango Well-Known Member

    Messages:
    408
    Likes Received:
    37
    Joined:
    May 30, 2016
    Location:
    Pittsburgh, PA
    ?? *I* said thanks...not sure what this post means?
     
    MiradaMegacab likes this.
  14. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,108
    Likes Received:
    242
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    Choot! I mean your welcome, lol.
    Sorry for the goof.
    And still goodonya for figuring it out.