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how to tell what axle ratio w/o pulling cover?

Discussion in 'The Garage' started by Cornfield creations, May 19, 2006.

  1. Cornfield creations

    Cornfield creations 1/2 ton status

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    Need to know how to find out the axle ratio on a 72 k-5 without pulling the diff. cover.

    Dealership said that it's stamped on the axle tube, between the spring and tire on the driver rear axle. I cleaned it off and didn't find anything.

    any help in appreciated
     
  2. resurrected_jimmy

    resurrected_jimmy 1/2 ton status

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    put a chalk mark on the driveshaft and one on the tire, jack the rear end up and turn the tire by hand 1 rotation while counting the number of turns the drive shaft makes. A little over 3 turns on the driveshaft = 3.08's, 3 3/4 turns of the driveshaft = 3.73's, and so on
     
  3. theperfectgarage

    theperfectgarage 1/2 ton status

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    Put a line on the drive shaft, a line on a tire, jack it up and turn the driveshaft by hand while counting the number of rotations ( including the fraction ) of the d-shaft to get one complete tire rotation. That should get you close enough. Ex; 3 and 3/4 turns on the d-shaft = 3.73 ratio.
     
  4. theperfectgarage

    theperfectgarage 1/2 ton status

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    wow, I hit enter and saw your post... your a smart guy.:D edit- takes me 15 min. for a quick post 'cause I'm at work.
     
  5. sandracer799

    sandracer799 1/2 ton status

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    Look up the RPO code in the glovebox.
     
  6. pvfjr

    pvfjr 1/2 ton status

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    I think you guys are sending him in the wrong direction.

    Assuming you have a open diff....
    You need to turn BOTH tires perfectly once, or ONE tire TWICE. Because of the operation of the spiders, you can turn one tire in two complete circles. This is the same as turning both tires in one complete circle, but a little easier to manage and a lot more accurate. So just jack up one tire, put a mark on it and the driveshaft, and turn the tire around twice and count the number of times that the driveshaft spins.
     
  7. theperfectgarage

    theperfectgarage 1/2 ton status

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    Whats an open diff?:D .... Very good point.
     
  8. atho

    atho 1/2 ton status

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    i 2nd the rpo sheet. if no gear ratio listed, what is the engine? if there is no engine indicated, does the VIN denote L6 or V8?

    my guess is 3.07, originally with a 350.
     
  9. Cornfield creations

    Cornfield creations 1/2 ton status

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    yeah i tried the vin code and the glove box, couldn't find anything. yeah it has a 350/350TH. I am hoping for 3:73, but I don't wanna waste my time getting the thing running so I can get it out so I can check the gears by pulling the cover.
     
  10. broncoman6524

    broncoman6524 1/2 ton status

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    I've gotta question bout the raisin up one side of the axle. Do you have to have the tire on to do it? Like say i was in a junkyard i dont wanna pull a buncha diff covers trying to find the right gears.
     
  11. MattK

    MattK 1/2 ton status

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    if the axle shaft is there to turn that will work as well. otherwise you'll be countin teeth.
     
  12. broncoman6524

    broncoman6524 1/2 ton status

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    alright i tried this on my truck today and i dont know WTF i did but it didnt work. I jacked up the Right rear tire put the T-case in neutral and tried to spin the tire. It was still locked into the Front driveshaft. I fired up the truck and played with the gear selector thingy until the truck wouldnt move on its own power. Still wouldn't let me turn the tire. I also tried it with the tranny and the T-case in neutral and it still wouldn't let me spin the tire.

    Is there something wrong with my T-case or could my hubs be stuck in the "Lock" position? (i have auto hubs)
     
  13. pvfjr

    pvfjr 1/2 ton status

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    You want the hub of the wheel you're turning locked in anyway. Otherwise, it won't be turning anything inside the diff, and that's what you need. If you have auto hubs, replace them. They're no good to anyone that wheels.

    Since you have auto hubs, I'm assuming you have what I'd consider a late model (anything 80's or newer is too new for me). This would also lead me to assume that you have a NP208 or a NP241. While I don't know as much about these transfer cases, I can tell you that a NP231 doesn't have a true neutral position. When shifted into "neutral" the front input is disconnected, but the front output is still coupled to the rear output, which would cause this problem of yours. This essentially means that the truck is still in 4wd while in neutral, but the tranny will not make it move. FOR THIS REASON, DO NOT FLAT TOW IN NEUTRAL WITH HUBS LOCKED. That's another reason to NOT have auto hubs, you never know what they're doing. Trucks with NP231's being towed with vacuum disconnect axles have had the cases literally explode into pieces under tow.

    Anyway, if this is what your case is doing, then put the t-case in 2HI, and put the tranny in neutral. See where that gets you.
     

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