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Minor front disc brake drag

Discussion in 'The Garage' started by RPC3, Jun 9, 2016.

  1. RPC3

    RPC3 XS650 Addict

    Just checking since I don't know and couldn't find an answer. My 78 standard has the stock caliper (fully rebuilt last year with a new piston and seals), new pads, a modern tw250 master (11mm I believe) cylinder and s/s one peice brake line. Brake works great. I recently got a jack so I was able to spin the front wheel freely and it drags just a bit on the pads. If I give the wheel a good spin I might get one full rotation. I can push the bike, I can drive the bike, but I wasn't sure how acceptable this was or not.

    I don't notice any issues at all when driving, but I am trouble shooting a minor front end bounce (just replaced the fork oil tonight, which is why I had the front end up).

    Anyway, thought it was worth the question. Thanks
  2. angus67

    angus67 Welder's penetrate deeper!!

    Disk brakes do drag a little, but sounds like yours is worse. U should be able to get a few spins. Have you rebiult the caliper? If it dosnt bounce when you first start riding , then it starts bouncing, could be the rotor heating up and warping. If its not alredy warped. Make a easy run out pointer to see if its flat.
    Another possible bounce issue....loose lock nuts on the stems.
  3. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Back in the '70's, as Honda was implementing hydraulic front brakes, we had a service procedure that involved setting the caliper position (on that pivoting mount), and checking for proper piston retraction of about 0.005", so the brake wouldn't drag. Any drag was bad, and would lead to heating, expanding the fluid, more drag, more heat, ...etc.

    Ever since then, I always check for this retraction during any disc brake servicing, hoping to get zero drag.

    I never knew how that retraction was accomplished, until joining this forum. Alway thought it was done by the master cylinder, pulling a slight vacuum near the end of brake release. Now, what i've gathered from the senior members' postings, is that the caliper piston's o-ring flexes back when pressure drops, retracting the piston. Please correct me if I'm wrong here...

    Sent from my Etch-a-Sketch using Scratch-and-sniff.
  4. jimschill

    jimschill XS650 Member

    Along that train of thought would it be possible that new o-rings would take a bit of time to "break in" and start retracting after a rebuild? Just spit balling
  5. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor


    A small amount of drag like you have is completely normal.


    No, seal rings do not require a break in period.

    Sent from my Acer desktop, using Google Chrome.:)
    gggGary likes this.
  6. RPC3

    RPC3 XS650 Addict

    Thanks RG, that's what I was hoping to hear. On a side note, pumping my forks got some of the nastiest black sludge I've ever seen to squirt about 5 feet across my shop. Wasn't getting much then I tried covering the fork top to create some suction and bam, sludge.
    gggGary likes this.
  7. 5twins

    5twins XS650 Guru Top Contributor

    Check your disc temp after a ride to see if the drag is too much. Lick your finger and touch the side of the disc. Yes, lick your finger. I've had bad ones sizzle the spit, lol. You know you have a drag problem if that happens.
  8. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    I agree with 5twins. A little drag is OK but a lot of drag is not good. The spit test seems like a good test for sure, unless you're a plumber by trade. In the first week of plumber trade school the instructor repeats many times, "You never lick your fingers":yikes:
    gggGary likes this.
  9. I currently have discovered that my front wheel is drangging really bad. I have had disc brakes on my Mountain bikes and was able to remove the wheel and very easily press in on the pistons with a closed end wrench. Can not press uneven or to firmly because you can crack the cryramic pistons. Any chance that I can use this trick on the moto?
    gggGary likes this.
  10. Mailman

    Mailman Hardly a Guru Top Contributor

    If you’ve never had your front caliper apart, you may very well have sticking pistons. Rust and corrosion builds up in there and seals need to be replaced. It would be a good idea to disassemble the caliper and give it a good cleaning, flush and replace all the brake fluid, it’s a good time to check components, and brake pads. The master cylinder also benefits from this treatment.
    TwinLewi and gggGary like this.
  11. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    77-83 model? Remove caliper from bracket one 12mm head bolt and the #2 phillips at the back now you can use a c-clamp to retract piston. I checked and you have a 73, Pistons can be sometimes be retracted with wedges screwdrivers, but a full overhaul is strongly recommended. I do a full brake caliper, master cylinder strip rebuild line replacement on any old bike. The XS system is simple, in dire need of cleaning, new fluid, new brake line. and it's critical it works right. With experience about 2 hours will do the whole project. Full brake rebuild how-to's can be found in tech.
    It helps to add your bike details to your signature so advice is appropriate to YOUR bike.
    Last edited: Oct 11, 2019
  12. Team Junk

    Team Junk XS650 Addict XS650.com Supporter

    They still make Etch a Sketch? I thought they had rebranded to Ipad.
  13. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Woth repeating; once fork leaks have gotten the pads oily there is NO cleaning method that works, they must be replaced. Think you got them clean? warm em up GOOD with a heat gun, watch, then go get new ones.
    wrenchjohns, TwinLewi, GLJ and 3 others like this.
  14. Yea a rebuild is probably best. Didn’t know if there were any tricks to eliminate drag. The bike did sit for a while in the weather. Just ordered a rebuild kit for the caliper with new pads. Fork was leaking and could have killed the pads. I rebuilt the forks to get that squared away. Brake lines appear to be in hood shape. No cracks.
  15. Great advice. Thanks for that. I will update my bike info. I will look for the how to for some extra guidance. Are you guys running the dot 3 or dot 4? I know new bikes are running mineral oil now a days. Would that be better or worse?
  16. 5twins

    5twins XS650 Guru Top Contributor

    DOT 4 is nothing more than a heavy duty, better version of DOT 3. I would use it if you can get it. If your lines are the original rubber ones, no cracks on the outside doesn't necessarily mean they're good. They could have gone soft on the inside which would allow them to expand under pressure, giving a "soft" or spongy lever feel. No amount of bleeding will cure that, line replacement is the only fix.
    wrenchjohns, gggGary and madmax-im like this.
  17. I agree. I might as well replace them if I am rebuilding the caliper. Could the same case be for the metal line? Or can I just soak in in break cleaner?
    gggGary likes this.
  18. 5twins

    5twins XS650 Guru Top Contributor

    I would think the metal lines are fine, as long as they're not all rusty or something.
    gggGary and TwinLewi like this.
  19. XSLeo

    XSLeo XS650 Guru Top Contributor

    Another reason calipers can drag is the return port in the Master cylinder.
    When you pull the lever it pushes the piston past the return port then builds pressure to operate the caliper. When you release the;lever the piston returns to its original position. This uncovers the return port. This lets all the pressure in the line to return to the reservoir. If this port is plugged the pressure can't return and holds the caliper party closed.
    YamadudeXS650C and gggGary like this.
  20. That is some interesting info! Makes sense to me. I am going to do a full caliper rebuild. Ordered a rebuild kit, pistons, pads and lines. Still looking for a rebuild kit on the M/C. Is there something I can/ should do on the M/C to clean out the return port?

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