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Breaking Rear Axleshafts!

Discussion in 'The Garage' started by 72THING, Nov 17, 2002.

  1. 72THING

    72THING 1/2 ton status

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    I have a rear D60 from a '79 F-250 in my truck. First things first, I got a good deal on it about 2 years ago, way back before I had planned on running big tires (39.5 TSLs). I realize now I should have gotten a 14 FF, but I have way too much time and money invested in this axle to ditch it now (gear and carrier change, disc brakes, custom spring pad width, etc.) /forums/images/graemlins/angryfire.gif I keep breaking axleshafts, usually in 2WD. This week I broke one while making a turn on the road! I know the rear end being welded is putting undue stress on them while turning on pavement. Randy's Ring & Pinion and Dutchman Axles both offer aftermarket alloy shafts for this axle, which are supposed to be a lot stronger than stock, probably about as strong as a factory 14 FF shaft, but I'm not sure if this is my best route or not. I've also read about converting the rear to 1.5" 35 spline by boring out the spindles, but there is a lot of expense in machine work and parts for this conversion. This would make it stronger than a 14 FF in the axleshaft department, but is mega bucks.

    I know almost everybody here runs a 14 FF and that's what I should have gotten, but unless I can find one with factory 4.56 gears, I can't justify the expense of getting one. I'm open to any suggestions and I appreciate the input.

    Will
     
  2. zcarczar

    zcarczar 1/2 ton status

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    Try and find a rear end out of a CUCV they have a Detroit and 4.56's and they should bolt right up to your 72
     
  3. 72THING

    72THING 1/2 ton status

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    Thanks, man. I'll keep my eye out for one. What is the most I should pay for one in good condition??

    Will
     
  4. bablazer73

    bablazer73 1/2 ton status

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    I think if you got a locker for your diff instead of welding, your current diff would be more reliable. welded spider gears puts alot of strain on axels when cornering. You can get away with it as a trail rig because the tires can skip on the trails and "unwind" the axels. But on pavement, the tires don't give to much.harder axels would help, but might not cure the problem.
     
  5. 72THING

    72THING 1/2 ton status

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    I've been thinking about this really hard and discussing it with friends. I have come to the same conclusion. A locker will be a lot more forgiving on the axleshafts. My solution is going to be buying a 14 FF. I went to the junkyard today and found a single wheel one ton 14 FF with 4.56 gears and open carrier for $150. /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gifThe one ton spring perch spacing I think will be about the same as my weird rear spring spacing (2WD truck converted to 4WD) and the axle is complete except for the straps & bolts that hold the driveshaft on, which is no big deal. I'll save up and get a Detroit No-Spin, put in new seals and disc brake brackets, and I'll be ready to go! Thanks for your help.

    Will
     
  6. bablazer73

    bablazer73 1/2 ton status

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    That sounds like a great deal. The lockers are only 325 and are easy to install.
     
  7. 6.2Blazer

    6.2Blazer 1/2 ton status

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    I very much doubt that just turning on the street was the real cause of the shaft breaking. Most likely it was fatigued, twisted, or partially fractured during a previous event like your last trail ride. While a Detroit might be slightly more forgiving on the street it still puts a lot more stress on the shafts and will stay locked unless you always coast around corners.

    You also need to consider the age of the axle shafts. If you are buying used shafts out of a junkyard they might have 200,000 miles which is lots of fatigue, no matter how beefy they are. One guy in our club wheels an old 40s-something Willys with the stock axles. He kept breaking rear shafts but was replacing them with 50 year old used parts. I finally talked him into buying new, yet stock specs, shafts and he hasn't broke one in quite awhile.
     
  8. 72THING

    72THING 1/2 ton status

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    At first I thought a welded diff. wouldn't really put more stress on the axles on the street, but I've broken three axleshafts (2 on pavement) and my friend broke both of his D70 1.5" 35 spline shafts on pavement, with the last shaft exploding with such force that it expanded the spindle from the inside out, ruining the whole housing. I really think there is less stress on the axles on the trail because the loose dirt/mud/rocks usually allows more tire slippage, therefore less stress. I think a Detroit Locker is still gonna put way less stress on the axleshafts than a welded diff. Plus, I still have to drive to and from the trail, so even if the Detroit still chirps tires, at least it can coast some of the time. I do agree that shafts with high mileage will be more fatigued, but I got a whole 14 FF with 4.56 gears in great condition for $150, which is still much cheaper than buying new shafts for my current D60. You may be right about the shafts being previously stressed, but I think making tight turns on the pavement greatly contributed to their premature death. Just my $.02.

    Will
     
  9. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Well, I'm sure the welded diff doesn't really help matters any but I still can't imagine there being enough stress while turning to ultimately break a shaft unless the shaft was already fractured. I would definitely say that climbing a hill (which causes a lot of weight to transfer to the back) with rocks while the tires spin, grab, and bounce would put way more of a shock load through the axle than turning ever would. If you are breaking shafts on the street just from turning, I would think you would also break them left and right everytime you went off-road. Also remember that when you turn, weight is transferred to the outside wheel thus meaning the inside wheel will be the one slipping due to the much reduced load on it.
    If you can go to a 14FF for a reasonable price, go for it because no matter what is causing the shafts to break you are still breaking them.
    This isn't directed at you, but I just like making sure people look a little further in vehicle failures and realize that something else rather than what initially appears as the obvious reason may not be the root cause (its what I do at work everyday). What the vehicle is doing at the actual time of failure is often not what actually led to the failure, but rather the "straw that broke the camel's back". It kind of goes along the lines of people talking about their 10-bolts "blowing up" just by backing out of the driveway so they must be junk....well no, backing out of the driveway was not the main failure. Or the people that say 700r4's are junk because they have rebuilt the one in their truck 7 times in the last 30,000 miles......even though the original one lasted over 100,000 miles, geez maybe the rebuild shop they are using sucks? Okay, enough rambling.........
     
  10. 72THING

    72THING 1/2 ton status

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    I understand that what the vehicle is doing at the time of breakage isn't necessarily the cause, but it seems that way. I also don't get why I always break the inside axleshaft when I turn, even though its the one with less load on it. I agree about looking further into the issue, so what should I do? I'm really not sure what to investigate or check out. Any suggestions?

    I'm not trying to argue with you, I just don't understand what is the main cause of breakage, or if its a combination of things. Oh well, I'll have a 14 bolt installed in a few months. Thanks for your help.

    Will
     
  11. andyzach

    andyzach Registered Member

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    have a 14bolt with 4.56 gears no locker for sale. 60 is just a weak rear end. a 70 is 70% stronger than a 60 and almost as strong as a 14bolt. a bbc 44's 4spd dosn't break my 14bolt /forums/images/graemlins/truck.gif
     

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