Broken Prothane Front LCA Bushing

Discussion in 'Suspension and Chassis' started by rgosda350, Aug 15, 2019.

  1. rgosda350

    rgosda350 TMO Beginner

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    Any one ever see this before? This is the front bushing on the left front LCA. The rearward facing bushing has had the shoulder shear or twist off.

    prothane broken bushing.jpg
     
  2. captdistraction

    captdistraction I am the breaker of things

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    Typical for those. I went through 4 sets. It’s a thrust force issue under braking. You can try to shim the rear bushing with very large washers but ultimately it just slows the rate at which they fail


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  3. 2012-Boss

    2012-Boss TMO Addict

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    Failure of the front poly bushing is not uncommon. If you don’t want to occasionally replace the poly bushing, you need to install an aluminum and delrin bushing. FRPP and Global West are a good source. I suspect the FRPP bushing is actually a delalum bushing from Global West.
     
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  4. BigTaco

    BigTaco TMO Addict

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    This.
     
  5. scmscout

    scmscout TMO Advanced

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    Delrin is the way to go.
    My prothanes lasted about 6 track days.
     
  6. rgosda350

    rgosda350 TMO Beginner

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    Will the OEM 2013 Boss EPAS rack work with Global West's Del-a-Lum bushings? Any worry about steering shake?
    Or will the Ford Racing EPAS rack be required with these?
    Car is used for Autocross on BFG Rival S tires, so not on R-comp.
     
  7. Grant 302

    Grant 302 OPM Spent: $665,833 Moderator

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    I wouldn't worry about EPAS nibble control issues unless you have an '11 or '12.

    I did feel it 'freak out' on my '11 once on the street when all stock and pretty new, but luckily hasn't shown up since.
     
  8. 2012-Boss

    2012-Boss TMO Addict

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    The Boss cars don’t have the nibble issue. It’s only the early GT models.
     
  9. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    Been thinking about this one a bit, and I'm not convinced that the failure can be fully explained by braking thrust.

    I'm seeing what looks like stress lines on the body side of the failure surface being at an angle, which tells me that the poly was also under some amount or torsional stress when it tore through. That it at least involved the stress intensification at the 90° junction is no surprise (the crack or tear probably originated there).

    Perhaps the installed length of the poly was longer than the inner sleeve that runs through it, which would turn some of the applied fastener torque into poly compression instead of useful clamp load. That would put torsion in the shoulder just due to suspension movement due to relative motion across the shoulder with friction on both sides. This would be happening all of the time that the car is moving, not just under braking.

    As a first cut, I wonder if this sort of failure could be postponed by trimming a little off the faces of the shoulders. Or more nearly eliminated by replacing part of the shoulder thicknesses with pairs of nylon/teflon/Delrin washers.


    Norm
     
    Last edited: Aug 17, 2019 at 7:44 AM
  10. scmscout

    scmscout TMO Advanced

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    Mine split the other way. If you look at the bore it has grease grooves, they are square, not round, bad design. I wonder if the square or sharp corner is another design flaw. I think these bushings fail for a lot of people. Go with delrin.
     
  11. captdistraction

    captdistraction I am the breaker of things

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    I wouldn’t put too much thought into trying to fix these, everyone I know with one glaring exception (who doesn’t run them anymore) has gone through multiple sets. Sometimes failing as quickly as one session. For the cost and hassle, the Delrin and FPP offerings are far better and more reliable.


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  12. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    Any sharp corner is a potential crack or tear waiting to happen, when the accumulated fatigue effects exceed what the material can handle.


    Norm
     
  13. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    This is one of those things I'd take a shot at just to see if I could improve it.


    Norm
     
  14. captdistraction

    captdistraction I am the breaker of things

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    I certainly tried. The biggest design flaw is removing the shell that had a face, leaving just the outer sleeve to cut into the bushing. I even looked at welding a lip into the arm to try and reduce it, but ultimately moved on to 302S/R arms and bushings which were not only more reliable, but made a noticeable difference in response over the prothane bushings when they were fresh

    The energy suspension bushing that keeps the oem bushing’s shell with lip doesn’t have the same issue. The bandaid I mentioned above about trying to shim the rear bushing with large washers to limit movement and provide support under braking and turn-in came from Jack Hidley at MM, they had some limited success there.


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