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Thread: How to turn a motorcycle brake drum?

  1. #1
    Join Date
    Apr 2002
    Location
    Northern VA
    Posts
    76

    Post How to turn a motorcycle brake drum?

    I have a Shoptask Eldorado 3-in-1 and would like to learn how to turn the brake drums on my motorcycles. I am restoring a 1970 Kawasaki G3TR and 1978 Yamaha IT175E, and both need their front/rear drums turned.

    My micrometer says there is enough material on all four drums to be turned and still have plenty left to stay within specs.

    But, how do I do it?

    Mu guess would be to chuck up the drums into the 4-jaw chuck and center them with my dial indicator. Would I then use a boring bar to carefully remove sufficient material to clean up the drums from the existing scoring? Would a HSS tool be correct, and what kind of RPM's would I need to be turning for the approximate 6" drums? Lubricant of some type?

    Also, how would I arc the new brake shoes to fit their specific drums?

    Finally, other than going to the local tech scbool and taking one of their machining/automotive courses, are there any books available which would tell me in detail how to do standard repairs such as this?

    Thanks a lot...did my first milling with the Eldorado last week and managed to earn $1000 for about four hours of work by modifying some Danish submachinegun magazines. Great learning experience and a darn good time, too!

    The Old Tom

    PS: My first learning experience while turning metal....use a BRUSH to clean up the swarf....it is SHARP and really imbeds deep into the old paws.

  2. #2

    Post

    hey tom, i've done brake rotors on a regular lathe and found that slow is best,minimal overhang on your boring tool is key to no chatter and smooth finish.set the bar as close to the tool holder as possible.and i've always found that a carbide tool is about all that will cut the work hardened surface of brake drums/rotors.also make sure drum/rotor is "dead nuts/balls on" centered or the resultant shimmy will lock wheel or throw you like a bad horse.DO NOT CUT SHOES!the material contains asbestos and the dust is very bad to breathe(causes asbestosis)the first few applications of the brakes will form the softer shoe to the drum/rotor. I usually test ride the bike and drag the brakes for 100 ft. to "mate" the new shoes to the drum.you'll feel the brakes get better in the first few days of riding the machine.hope this helps,be careful,have fun.

  3. #3
    Join Date
    Apr 2001
    Location
    Maine
    Posts
    6,681

    Post

    Never having done this, and not knowing the exact configuration of the brake drums....

    I'd be inclined to make up a special faceplate or other fixture to mimic the way the drums are mounted on the motorcycle. Then bolt them in place as they are normally bolted in place, and machine. I have a hunch that trying to set them up in a 4-jaw would be a PITA and not very satisfactory.
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.

  4. #4
    Join Date
    Nov 2002
    Posts
    138

    Post

    I have a 1970 CT 175 yamaha if you are interestd. It seems to have good compression, though i havent had in running yet. I am in connecticut and would like to get $100 for it. I dont know what is interchangable with your bike.
    merf23@yahoo.com

  5. #5
    Join Date
    Nov 2002
    Posts
    48

    Post

    he he twist the throttle. couldn't resist.

  6. #6
    Join Date
    Nov 2002
    Location
    Maine
    Posts
    1,439

    Post

    I've done motorcycle brake drums in a lathe by mounting them on a stub mandrel.

  7. #7

    Exclamation

    SqueakyTom:
    You will need to mount them the same way they are on the bike (a hub or stub axle) to insure they are cut concentric with the axis of rotation, otherwise you will get "pulsing" of the brakes. Brakes are one of the few things that have to be done properly to ensure safety - a little extra effort is well worth it.

    Have fun!

  8. #8

    Post

    Tom,

    Bad news! the only way of ensuring brake drums are truly concentric is to machine them in the wheel if they are laced in ~ don't know what US spec 1970 Kawa 3's were like but UK versions had spoked wheels with the spokes laced off the drum flange. Might need an Oil country lathe to swing the wheel complete!!

    Even retensioning the spokes will upset the drum concentricity. On Fontana double sider 4 leading shoe brakes the manufacturer stated that ANY retension or spoke rebuild would require a skim to true it up 'with the brake mounted in the finished wheel assembly'.

    To bed the shoes in quickly (and help dust/debris removal from the drum face ~ which will help prevent future scoring) put 3 diagonal saw cuts across the face of the shoe by half the shoe thickness, and ease down the leading edge of the shoe with a file. As BikeWrench stated - beware ofthe dust ~ although all modern friction material is these days 'non asbestos' don't take any risks!

    RR

  9. #9
    Join Date
    Dec 2002
    Location
    Friesland, Netherlands
    Posts
    1,834

    Post

    Tom,

    Have a close look for cracks in the drum linings - I've seen a couple of 1970's vintage Hondas like this, which I believe used cast iron liners cast into the alloy hub. If the lining collapses, the brakes might suddenly work REALLY well...

    Good luck,

    Ian
    All of the gear, no idea...

  10. #10
    Join Date
    Apr 2002
    Location
    Northern VA
    Posts
    76

    Post

    All,

    Many thanks for the comments....I will end up getting a test drum turned by a friend at a local brake shop to see exactly how it is done.

    Then, it is time to make a stub mandrel and turn a test drum on the lathe.

    Then...

    Time to turn the real ones on the lathe. I understand the comment about turning them while laced up, but, I believe the factory did not do it like this back in 1970. They turned them while separate from the spokes, etc. and then laced them up.

    Finally, I am real glad to hear about carefully checking them for cracks. This will be done very closely, indeed! It would be quite embarrassing to have the hub fail while taking a turn late one night (or day).

    The Old Tom

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