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Thread: Semi trailer brake spider repair

  1. #1
    Supporting Member Frank S's Avatar
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    Semi trailer brake spider repair

    on semi trailers there is what is termed as the spider this is what the brake shoes and the "S" cam actuator shaft mounts to Over time the bores can be come worn. On the show mount side it is best to ream these out and press in a sleeve the sleeves are often provided in new hardware kits However on the "S" cam side the bearing or bushing if you will is made of plastic and no sleeves are never provided in fact they are not even produced or sold. You choices for repairing these locations boils down to either welding them up and line boring them back to size. or line boring them to a larger size and machining your own sleeve to press in or you can rough grind them with a dermal stone and repair them with a metal empregnated high temp epoxy.
    obviously one of the line bore methods would be preferred but also the most expensive and time consuming. The epoxy method will usually last for years with the plastic bushings on the semis that have the bronze bushings line boring and repairing would be much better.
    Here's what I did I turned and ground a piece of tubing to a .020" undersize OD of compared with the new plastic bushing this was to allow for the finished bore of the repair to give the proper crush on the bushing
    Semi trailer brake spider repair-wp_20200826_10_31_45_probh.jpg
    I then used a Dremel stone in a drill to grind the ID of the locations leaving it rough and in the shape of the wear.
    Semi trailer brake spider repair-wp_20200826_13_05_43_probh.jpg
    Then after making a full set of arbors or sizing mandrels I wrapped them in plastic kitchen wrap this was to insure the epoxy could not fuse with the mandrels don't worry about a few wrinkles in the plastic wrap it is so thin they wont matter very much anyway.
    Semi trailer brake spider repair-wp_20200826_13_30_57_probh.jpg
    Next mix the epoxy fill the bore and inset the mandrel
    Semi trailer brake spider repair-wp_20200826_14_50_24_probh.jpg
    leave the mandrel in until the epoxy is fully set but not completely cured, the Epoxy I used said set in 6 to 10 minutes hard in 6 hours machinable in 24 hours
    I removed them after 20 minutes and was able to trim the excess with a sharp knife saving me a lot of grinding or sanding later

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  3. #2
    greenie's Avatar
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    Have to ask this question ------------- what will happen to the epoxy, once the heat starts to be generated from the brake shoes being applied ?

    I have seen brake drums glowing red, from overuse of the brake pedal by imbeciles at the steering wheel. All that heat is transferred to all place close to the brake drums and that S cam is surely very close to all this heat being generated.

    Even a cautious driver will make the wheel bearings very hot to touch after a long downhill run, so I can not see the epoxy lasting very long at all, then you'll have a bunch of very defective brakes on your trailer, when you are relying on them the most.

    Psst, -------------- hope you got GOOD health insurance.

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  5. #3
    Unkle Fuzzy's Avatar
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    greenie...the factory bushings are plastic.



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    Frank S (Sep 3, 2020)

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