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Thread: "Weak" axles

  1. #1
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

    Default

    OK some discussion has taken place regarding the axles in these things, and their survivability behind more powerful engines. Let's take a look.

    The front axle is rated for 935 lb-ft of torque.
    The rear axle is rated for 1,450 lb-ft.

    Divide these ratings by the combined low gears of the transmission and transfer case, to get a worst-case value. Transmission 1st [6.398] X transfer case low range [1.96] gives us a multiplication factor of 12.54. This 12.54 x axle gear ration =
    crawl ratio, or 73.6098:1, but that's not important in this discussion.

    Then, the stock engine is rated at 191 net lb-ft of torque. So in high range (Transfer case) and 4th gear, the axles would see a total of 191 lb-ft of torque. Child's play. Now, multiply the 191 by the factor above [12.54], and we see that the axles then receive 2,395.14 lb-ft. WOW! If we suspect that the front axle will do 39% of the work, and the rear does 61%, we see that the front receives 934 lb-ft (rated at 935) and the rear receives 1,461 lb-ft (rated at 1,450), and we clearly see that the axles are right up against their design limits in low-low, with the original engine (when operated at the most extreme end of the vehicle's capabilities)! Then you get into the situations of shock loading where spinning tires suddenly find traction? Ugliness may soon follow.

    Naturally, there are other factors to consider. The degree of "go-pedal" used, state of tune of the engine, and perhaps more importantly, does one ever stress the truck to the point of stalling the engine in low-low at WOT? I did in a truck pull, may not again after seeing these numbers!

    Is it any wonder that these axles CAN fail when the truck is repowered with an engine that produces two to three times the torque of the 1bbl Tornado?

    Now, I'm a big fan of these trucks. I applaud those who wheel them, resore them and modify them. I'm NOT slamming these trucks. At all. This is just a posting of the results of my study of the manuals here on-line.

    Makes a bit of sense now to keep the itty-bity u-joints, huh? Easier and cheaper to change than an axle!

    Food for thought.

    Bob

  2. #2

    Default

    Bob, Has it been slow lately.
    I don't think that I could think that deep.
    redneck1

  3. #3

    Default

    your scholarship is noteworthy. Thank you for the tutorial. I always wondered what the torque at the axle was on the stockers.
    The above illustrates why I'm a fan of the 14bolt as well. Also why I'm spending most of my money on the axles and not the motor.
    I'd bust out the Nomex, the stock guys are going to fry you for that one LOL....
    **I heart Bump_r **

  4. #4
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

    Default Spring rates

    Fry ME for reporting what is in the freakin' manual? I think not. I'd think they'll bask in the glow of their wisdom for keeping the Tornado.
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  5. #5

    Default

    Hrmph. Optimist. Could you be so kind as to post the formula to calculate torque at the axle? I know it's in your other post , but I mean in a straight out form. I hate math.
    **I heart Bump_r **

  6. #6

    Default

    That is a really great post Bump !! Add to that the wheel spin that the open rears allow transfering ALL the power to the wheels with the least amount of traction. Now We put in lockers and a real set of traction tires . Now what follows is even uglier !!! The wheels with the MOST traction MUST turn. BANG !!! Twisted off axle shafts. I've been there and done all that. I've broke NOS shafts in less then 5 minutes. It's no fun being broke . M1028
    If your not breakin\' something - Your NOT makin\' enough torque !!

  7. #7

    Default

    I'm trying to decide what to make the weak link: the easiest part or the cheapest LOL. I suppose if I make it the easiest it will cost me. If I make it the cheapest (front u-joints I guess) then it will be a pain in the ass. Have seen some very interesting ways to secure a vehicle out here.. and none of them were very safe lol..
    Maybe the front driveshaft u-joint, as it is both easy AND cheapish.

    anyway post that formula, I want to compare apples. And I feel sort of lazy today too....flu bug.
    **I heart Bump_r **

  8. #8
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

    Default How do you degree a cam?

    Engine torqueXtransmission gear ratioXTransfercase ratio=torque applied to axles. pick any gear/transfer case range you please.

    This does not take into account parasitic losses. Nor does it specify front-to-rear bias - I just noted the 39%:61% based on torque specs listed in the manual. [front spec/(front spec+rear spec)] and [rear spec/(front spec+rear spec)]
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  9. #9

    Default

    Tacoma, We argue the weak link point alot . IT seems that the only time that something breaks is when you really need it. Two feet deep in mud and a front driveshaft joint lets go, taking a piece of the yoke with it. Or worse yet putting a hole in the oil or tranny pan. That is not my idea of a fun time or a well built truck. M1028
    If your not breakin\' something - Your NOT makin\' enough torque !!

  10. #10
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

    Default

    Agreed. Conventional wisdom states that a $12.00 u-joint should be the weak link. I agree with that as long as you have a drive shaft hoop to retain it!

    Warn makes front hub fuses, but they tend to 'splode differentials when the let go. Not exacly my idea of a safety device, no?
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

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