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  1. #1
    Newbie
    Posts
    1

    brakes sticking on 1980 KZ750

    I've never had a motorcycle, but by the grace (or curse) of God, I've been blessed with two identical 1980 KZ750s, one to ride and one for parts. The front brakes have been sticking... slowly closing down, even while it sits overnight! I pop the bleeder and they're ok for a bit, but it's dangerous!
    I bled the lines, and the fluid was dirty, and it helped a bit, but still toooo dangerous. I swapped the calipers, and bled them and it's a lot better, but they still slowly close down over time. I swapped the master cylinder, but cannot bleed it successfully! I open, pump, close, open, pump, close, 4FR (forever!) and nothing happens. Air bubbles keep coming out of the two little holes in the bottom of the master Cylinder's Reservoir.

    Any ideas as to WHY the calipers close down over time?
    Any ideas as to how i can tell if the master cylinder is any good?
    Any ideas on a fair price to have it rebuilt?
    Any ideas on a fair price for a new one?
    Any ideas on where to get that fair price?

    This is my 1st post on any forum anywhere. Am i being too wordy?

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  3. #2
    Top Gear ! Full Throttle!
    My Bike(s)
    2010 Hayabusa... a black one... the fastest colour
    Location
    Perth WA
    Posts
    5,218
    Hey welcome Jimj

    I have never had the same problem you have mentioned so I am unable to help. If the pads are coming out on their own I guess you must be getting pressure build up from somewhere. Just a thought are the pistons easy to push back in? If not perhaps when you pull the lever the pistons only operate slightly and over time the pressure build up pushes them out....like over night.

    Sorry I cannot be of any more help...usually the pistons seize in or out. Do not worry though someone here will be able to help.

    Regards

    Steve
    Smoke me a kipper I'll be home in time for breakfast

  4. #3
    Found second gear by accident
    My Bike(s)
    I'm lucky, I've got alot
    Location
    minnesota
    Posts
    328
    Brakes are awful important. A complete rebuild of the master cylinder, calipers (whichever ones you're going to use) and replacement of the brake lines would be a great start.

    The bike is headed for 30 years old. New fluid is a great measure to keep all the parts working well. I'd say the fluid has never been changed, or seldom, during the life of the bike. Everything is probably suffering from years of neglect. Go through the whole system.

    If you can't rebuild the parts yourself, take them off, to a dealer, and get the tricky stuff done right. It'll cost a bit, but you'll still be around to complain about it. I wouldn't mess around with looking for a cure to the symptoms. I'd just do it all and stay alive. Once again brakes are awful important.

    MOTO GUZZI

    loud valves save lives


  5. #4
    Found second gear by accident
    My Bike(s)
    2003 MeanStreak 1500
    Location
    Manassas, VA
    Posts
    308
    Quote Originally Posted by jimj View Post
    I've never had a motorcycle, but by the grace (or curse) of God, I've been blessed with two identical 1980 KZ750s, one to ride and one for parts. The front brakes have been sticking... slowly closing down, even while it sits overnight! I pop the bleeder and they're ok for a bit, but it's dangerous!
    I bled the lines, and the fluid was dirty, and it helped a bit, but still toooo dangerous. I swapped the calipers, and bled them and it's a lot better, but they still slowly close down over time. I swapped the master cylinder, but cannot bleed it successfully! I open, pump, close, open, pump, close, 4FR (forever!) and nothing happens. Air bubbles keep coming out of the two little holes in the bottom of the master Cylinder's Reservoir.

    I think what I did was:
    open - squeez brake - close - release brake. And to repeat the guy above this post...just replace all the main parts. And if you don't feel comfortable have someone do it who does.



    Any ideas as to WHY the calipers close down over time?
    Did you replace with new calipers? I had the same prob w/ my savage a while back and I needed a new piston in the caliper. There was grime and dust and it didn't allow it to move freely in and out. Prob also needs to replace piston/dust seals.

    Any ideas as to how i can tell if the master cylinder is any good?
    Any ideas on a fair price to have it rebuilt?
    Its not really too difficult...if u can take the caliper off you should be able to push out the piston[s] and inspect it/replace it(it there's pitting then replace it). Then replace the dust and piston seals.
    Dan's Motorcycle "Hydraulic Brakes & Clutch"



    This is my 1st post on any forum anywhere. Am i being too wordy?
    Last edited by d_m50; 04-23-2007 at 08:31 AM.
    90$ M50 Final Drive


 

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