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Thread: Forks jump when braking

  1. #1
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    Default Forks jump when braking

    I have cleaned the rotors ( both front ones ) with brake cleaner spray and new paper towels, spun the wheel off the ground and observed each rotor and not a wobble to be seen, pads are new. When I brake it feels like a warped rotor on a car feels but i can see the fork lowers slightly jumping up and down as I brake. Never have had this before so I am at a loss. Any pointers???

    I was thinking maybe bearings but then why would wheel bearings make the lowers twitch and there isnt any signs of bearing wear or slop when i spin and twist on the rim???
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C(X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

  2. #2
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    Default

    Any pitting in the fork tubes? Maybe too much compressed air? When was the last time you changed the fork oil?


    Ed
    GS750TZ V&H/4-1, Progressive Rear Shocks, Rebuilt MC/Caliper & new single-braided front line, Tarozzi Forks Stabilizer[Seq#2312]
    GS750TZ Parts Bike [Seq#6036]
    GSX-R750Y (Sold)

    AKA: "Red" as named (Affectionately) by Gramma P.

    Quote Originally Posted by GSXR7ED
    Forums are pretty much unrecognizable conversations; simply because it's a smorgasbord of feedback...from people we don't know. It's not too difficult to ignore the things that need to be bypassed.

  3. #3
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    Default

    Loose steering head bearings?

  4. #4
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    My dads 850L did this and it was the caliper axle/ bolts were stuck with old grease and wouldn't move, I took them out cleaned the 30 year old grease and it fixed the wobble. That would explain the braking and no wobble visually when rim is spun
    -James
    1982 GS850g done
    1980 GS1000g- (current build)

    1980 Gs1000g w/1100cc -old blue.

    “The most important days in your life are the day you were born and the day you find out why.”- Mark Twain


  5. #5
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    Default

    New seals and new oil. No pitting in the tubes. Bike is an 81 750L and I did notice the calipers do move on the pins when i squeeze the lever. Rebuild kit in the master and its the round resivoir style master cylinder.

    I will reinspect the carriers for sure. I can litteraly look down and watch the lowers go up and down on the tubes..much like its a jack hammering action going on down there. harder i squeeze the lever the more pronounced it becomes too.
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C(X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

  6. #6
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    Chuck, can you lay hands on a clamp on dial guage? {magnetic won't do you any good}
    Or, is there a parts supply place you can borrow one from {advance auto/napa....} It's hard to see a wobble/warp in the rotors....obviously if you actually see it - it's bad!...but it's the stuff you can't easily see that can be a problem too.
    The only way "I" can see the lower fork legs moving on you like that is due to a brake pulse...explains why the harder you grab the brake, the worse it gets.
    I'd suggest putting the bike on the center stand and try moving the front wheel side to side {one hand on top of the wheel and the other on the bottom}....looking for bearing slop. If the bearings are bad that could cause the brakes to grab unevenly...had a bad set on my FJ1100...couldn't feel it in the brakes, but I could feel it at low speed and by using my hands {side to side}.
    ...my work bench was clean last week - sorry you missed it

  7. #7
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    I warped 3 sets on my EZ. When my brake lever started pulsating I never thought past the rotors being warped. Thats what it always was.
    82 1100 EZ (red)

    "You co-opting words of KV only thickens the scent of your BS. A thief and a putter-on of airs most foul. " JEEPRUSTY

  8. #8
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    Set up an indicator and measure the runout on the wheels and rotors. I bet they're warped. If not, it's wheel bearings.
    Johnny

    Artificial Intelligence is no match for natural stupidity.

    '82 GS1100GK - Max
    '83 GS850G - Minnie
    '83 Yamaha XJ650 Maxim

  9. #9
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    I will, see if i can get hold of an indicator.
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C(X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

  10. #10
    Join Date
    May 2007
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    muskegon, mi
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    1,850

    Default

    chuck, harbor fright has a passable clamp on one for like 15 dollars or something.
    1983 GS 1100 ESD

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