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  1. #1
    Join Date
    Aug 2011
    City/State
    Pensacola, FL
    Scrambler Year
    1981
    Posts
    66

    Question AMC 20 - Axle Bearings / Seals

    Okay, so I've removed the axles from my AMC 20, and am about to put it all back together - these are two piece axles, and my brake backing plate will not allow the inner bearing to pass though. As I understand it, the order of the parts is the following:

    Inner seal > Axle with bearing pressed on, tapered side out > Race (or bearing cup) > SHIM(s) > Brake Backing Plate > OUTER seal (aka: axle retainer plate) > Outer seal retainer > Hub (with key in place).

    Correct me if the above is wrong.

    The SHIMS are to go between the housing flange and the Brake Backing Plate correct?

    Also, I can't find any specifics on the SHIM use .. when I disassembled my AMC 20, there was 1 SHIM on one side, and 3 SHIMS on the other.

    I've read where they are used to "pre-load" the bearings, which I assume means reduce / remove slack, but can't find any details on the calculations or testing to confirm .. I've seen details on one-piece axles though.

    Any help?

  2. #2
    Join Date
    Aug 2011
    City/State
    Pensacola, FL
    Scrambler Year
    1981
    Posts
    66
    Wow .. this must be a tough topic.

  3. #3
    Join Date
    Jul 2009
    City/State
    Gordonsville, VA
    Posts
    900
    Either take the hub off the axle and put the backing plate on, or press the bearring on with the backing plate already on the axle.

    You order of parts is correct.

  4. #4
    Join Date
    Aug 2011
    City/State
    Pensacola, FL
    Scrambler Year
    1981
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    66
    Quote Originally Posted by Jeeperdd View Post
    Either take the hub off the axle and put the backing plate on, or press the bearring on with the backing plate already on the axle.
    It is all taken apart, was asking about the shims .. I have confirmed that the shims go between the flange and the backing plate, but hadn't found the technique for defining how many ..

  5. #5
    Join Date
    Feb 2009
    City/State
    Biloxi, MS
    Scrambler Year
    1983 (I think SR?)
    Year Purchased
    2009
    Posts
    3,171
    The shims go between the axle housing end and the backing plate. They only go on one side, can't remember which off the top of my head.

    YOU MUST HAVE THE FACTORY CENTERING BLOCK INSTALLED IN THE DIFF IN ORDER TO USE THE SHIMS.

    It goes something like this: Install one axle, tighten it down, make sure it "bottoms out against the centering block. Install other axle, check "in/out" play with axle tube mounted dial indicator. Adjust the "play" with shims to get the correct end play. You only shim one side. If the centering block is not wore out, the two axle shaft end ride against it. The shims on the ones side allow just enough "float" to keep the bearings from burning up.

    Be advised, if the centering block is wore, you need to replace it. A wore center block will cause too much play in the outer bearings, leading to leakage and/or bearing failure

    The FSM goes into great detail compared to the Haynes/Chiltons Manuals. Also, the 250 ft pounds of torque on the axle nuts is a "STARTING POINT ONLY". There is a measurement, from the end of the axle threads to the face of the nut, that is critical. It usually takes me quite a bit more torque then 250 ft pounds to reach the measurement, i.e. 3/4 drive ratchet with a 3' handle and a 6' cheater pipe. Be careful, once you tighten it too much, game over

    The two axles with the centering block make up a complete unit, like a solid axle from side to side. That is why it is shimmed only on one side. If the axle ends/centering block have too much wear, you will have too much slack in the bearings, leading to leaks/failure.

    Most of the one piece axle kits use a "unit bearing", i.e. the bearing and race are assembled. They are built with the necessary "play" already. This is why you don't "shim" most one piece axle kits.
    Last edited by spankrjs; 01-08-2013 at 12:52 PM.

    1983 Sherwood Green CJ-8 - mostly stock SR
    1983 Sebring Red CJ-8 - completely rebuilt, originally Base model
    1984 Almond Beige CJ-8- original paint, TBI 350/700R4/CA rust free project, Base model
    1983 Sherwood Green CJ-8 SR - "project yard Scrambler" - "SOLD" back to JeepAddict
    2005 LJ Rubicon Flame Red - all stock, daily driver

  6. #6
    Join Date
    Aug 2011
    City/State
    Pensacola, FL
    Scrambler Year
    1981
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    66
    Quote Originally Posted by spankrjs View Post
    The shims go between the axle housing end and the backing plate. They only go on one side, can't remember which off the top of my head.
    The FSM states "the left side."

    Quote Originally Posted by spankrjs View Post
    YOU MUST HAVE THE FACTORY CENTERING BLOCK INSTALLED IN THE DIFF IN ORDER TO USE THE SHIMS.
    I assume you'd only have the centering block (thrust block?) removed with the chunk? I wasn't sure the circumstances where the centering block would not be present at this point of reassembly.

    Quote Originally Posted by spankrjs View Post
    It goes something like this: Install one axle .. shims on the ones side allow just enough "float" ...
    Nicely written .. from what I've found, this is exactly the procedure. I just haven't figured out what a "axle tube mounted dial indicator" is ..

    Quote Originally Posted by spankrjs View Post
    Also, the 250 ft pounds of torque on the axle nuts is a "STARTING POINT ONLY". There is a measurement, from the end of the axle threads to the face of the nut, that is critical.
    The FSM refers to that measurement only in the section where you are replacing the axle and hub .. but I get the impression that that exposed thread measurement should be the same either way.

    Quote Originally Posted by spankrjs View Post
    Most of the one piece axle kits use a "unit bearing", i.e. the bearing and race are assembled. They are built with the necessary "play" already. This is why you don't "shim" most one piece axle kits.
    Good point .. a lot of what I found was unclear on this point, leading to more confusion. There's more on the Internet about reinstalling one piece axles that two piece .. from what I found.

  7. #7
    Join Date
    Feb 2009
    City/State
    Biloxi, MS
    Scrambler Year
    1983 (I think SR?)
    Year Purchased
    2009
    Posts
    3,171
    The centering block is located on the differential cross shaft, between the side gears. The only way to remove it is to pull the diff out, remove the spider gears and shaft, then reinstall. Hopefully, yours is still there

    One thing I need to clarify: The backing plates prevent the axles from moving "outward". The centering block prevents the axles from moving too far "inward". My centering block had excessive wear, the axles/bearings would not move out much, but they would move in too much, causing the seals to leak. When I installed Moser axles, the centering block kept the axles from going in all the way. I had to pull the chunk and remove the centering block. That's why I know this stuff


    Let me see if I can find a picture of the dial indicator. Good ones are expensive, you might want to see if you can borrow one







    Not the best pictures, but they show me using a dial indicator to check the back lash on a ring and pinion. Some people do this by "feel", I like to know that the little gauge agrees with my "feel"
    Last edited by spankrjs; 01-14-2013 at 12:59 PM.

    1983 Sherwood Green CJ-8 - mostly stock SR
    1983 Sebring Red CJ-8 - completely rebuilt, originally Base model
    1984 Almond Beige CJ-8- original paint, TBI 350/700R4/CA rust free project, Base model
    1983 Sherwood Green CJ-8 SR - "project yard Scrambler" - "SOLD" back to JeepAddict
    2005 LJ Rubicon Flame Red - all stock, daily driver

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