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final drive ratio?

Discussion in 'Early CJ5 and CJ6 Tech' started by red61cj5, Oct 28, 2011.

  1. red61cj5

    red61cj5 Just fell off the turnip truck!

    This is probably a stupid question, because I must be missing something obvious, but why does my rear driveshaft only rotate about 2 3/4 turns for one turn of the rear wheel? I thought this was how you got a rough idea of the gears in a vehicle. The rear end tag states 5.38, which is about what I figured should be in it. I cant imagine anyone putting car gears into one, but Ive seen some weird stuff before. While on the subject, what axles are under this thing anyway? I dont see any identification, but its still prettty grimy underneath. Its a 61 cj5.
     
  2. duffer

    duffer Rodent Power

    I am going to bet you only have one rear (or front) wheel jacked up-makes the tractionless wheel turn twice as fast since the other side is not moving.
     
  3. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Yep. Both rear wheels have to make a complete rotation for 5.38 rotations of the driveshaft. If one doesn't move, the other has to move twice as many turns. That's how differentials work - they divide the total rotation between both wheels, sometimes one wheel more than the other. 2.75 * 2 = 5.50 ~ 5.38.
     
  4. red61cj5

    red61cj5 Just fell off the turnip truck!

    Ok, I guess Ill strap on my helmet, get back on the short bus and lick the window for a while. I knew the answer was obvious. How about the axles, assuming they are the originals?
     
  5. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    The two-rotations thing is a common misunderstanding. Don't be too hard on yourself.

    What are you asking about the axles? 5.38:1 is the most common ratio in the F134 CJs. Some came with 4.27s. Your measurements say that the 5.38 ratio is right - counting the driveshaft rotations is only approximate, esp. when you divide the result by two :)
     
  6. oldtime

    oldtime oldtime

    Stock Standard 1961 CJ's are always 5.38 final drive with no exceptions.
     
  7. Warloch

    Warloch Did you say Flattie??? Staff Member

    The problem being - unless you bought it new your self you just don't know. I bought a 'stock' 62 CJ5 that has 4.27s under it...
     
  8. red61cj5

    red61cj5 Just fell off the turnip truck!

    No, I mean dana 30's, amc 20's, what are they? Theyre both offset to the passenger side, but thats all I know. The only ones I can recognize by sight are 9 inch fords and sterling 10.5's. Pretty sure it doesnt have those. Would be a killer setup though, huh?
     
  9. unclebill

    unclebill Banned

    thats why you told me to ignore the tags and make certain of mine....
     
  10. red61cj5

    red61cj5 Just fell off the turnip truck!

    And you're exactly right, Warloch, the thing has a fiberglass body and an alternator instead of a generator, which I thought was stock, so I really dont know what the guy before me might have done to it. Im just glad he left it behind, this stuff is way more fun than golf. Of course so is watching paint dry.
     
  11. duffer

    duffer Rodent Power

    Rear: D44
    Front: most likely a D27 but could be a 25
     
  12. Warloch

    Warloch Did you say Flattie??? Staff Member

    Duffer is right, you will need to get an account so you can get pics to post if your new to this. A picture here is worth more than a thousand words due to the fact many things can and do change over the years. There will be a stamp on the web on the top on one side (escapes me which right now) or the other of the front diff with a 25 or 27 on it. Other than some internal dif parts (ring and Pinion comes to mind most) the 25 and 27 are interchangeable.
     
  13. andy howell

    andy howell Member

    hey red61 several years back i had some metal parts hanging from the chain hoist frame & had just sprayed the 1st coat of top color so i went to the house to get a glass of tea. when i came back they hadn't flashed good yet so i just sat down to wait a few minutes. my buddy came up & asked what i was doing. i told him "watching the paint dry". he looked at me like i was a three eyed cow, shook his head & left. some folks just don't get it. by the way, which willys vehicles came with 4.88 gears? i bought an m38a1 in a junk yard kinda a "over the phone through the fence" deal & when i went to get it i was suprised to find it was a wagon or a truck shortened up with a a1 body on it. i hope the axles have 4.88s in them, but i'm usually not that lucky.
    andy
     
  14. Warloch

    Warloch Did you say Flattie??? Staff Member

    'Most' rigs with 4.88s are the late 60s to 71 with the V6 as the 4.88s were an optional axle ratio. I can not speak to the trucks and wagons as I don't have them off the top of my head.
     
  15. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Re the truck axles, it depends very much on what year/model the truck was. Could be anything from 2.73 to 5.38.