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Front disk brake dragging!

Discussion in 'The Garage' started by Excess Impulse, Jun 17, 2017.

  1. Excess Impulse

    Excess Impulse XS400 Addict

    I have a 1980 XS400 , I have rebuilt the caliper with new seals, cleaned up the piston, rebuilt the master cylinder, have new brake pads, and have all new brake fluid in it. It is Okay to use DOT 4 fluid isn't it? After doing the rebuilds it was a challenge to get the air out but was able to finally by using a hand held bleeder. On the 1st test ride after work was finished I noticed the front brake dragging hard, and I squeezed the brake lever and cracked the bleeder, this solved it. Today was the 2nd time I have really ridden the bike out on the road as I have been working on it off and on for the past year or so. Once again the brake started dragging, rotor was hot and brake was squeaking. My question is, is this just dirt in the system yet, is it trapped air? I sure don't want the brake locking up on me. I did apply the brake and crack the bleeder again and the brake released, but have a feeling this will keep happening. Any suggestions?
     
    Last edited: Jun 17, 2017
  2. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    Stop riding the bike, it is unsafe. You are playing Russian Roulette with everyone else around, every time you ride. Please don't kill anyone.

    DOT 4 fluid is fine in a DOT 3 system.

    Check the brake lever adjustment (free play) on the master cylinder. If that is correct (not what you want, correct), then clean the master, making sure the tiny ports are all clear. Replace the brake line if it is more than 10 years old, as it may have collapsed internally. While you are at it, service the caliper, being sure to clean and lube the slider pins so they move smoothly.
     
    kshansen likes this.
  3. Excess Impulse

    Excess Impulse XS400 Addict

    Dave, Thanks for your reply. Yes I did stop riding it. After the 1st time out I had thought it was fixed but soon found out it was still hanging up. I have cleaned and rebuilt the master cylinder, as well as the caliper, installing new seals in both. Have new brake pads and fluid. I didn't replace the hose however as it didn't look too bad but it most likely is the original 37 year old hose so that might be the issue. The piston was moving easily in the caliper and the pins were clean and lubed. I will look up the correct setting for the lever adjustment, but there is free play before it starts to push in the piston on the master C. I have looked at the forum and see some have used the HEL braided line so that looks like the next and hopefully last part to replace.
     
  4. Jeff0133

    Jeff0133 XS400 Junkie Top Contributor

    Check the tiny port in the master cylinder...it is the "vent" port for when the brake is released, the fluid can return to the master cylinder, if it is blocked partially it will cause your brakes to drag or lock-up
     
  5. Excess Impulse

    Excess Impulse XS400 Addict

    Thought I would post a quick update to this thread. After cleaning and rebuilding the caliper and the original master cylinder and still having problems with front brake drag, I figured the problem must be the 37 year old brake line, so I ordered the braided stainless one from the good folks at HEL. I also ordered a new master cylinder off Amazon, and am awaiting the delivery of both these. I will remove the caliper and clean it out again, as my guess is the old brake hose had deteriorated and caused debris to get into the caliper. This is the master I ordered, I know it's a cheepy, but hope it works out for me. It says the bore is 14mm, which is a little larger than the stock master. https://www.amazon.com/PanelTech-Mo...rds=motorcycle+master+cylinder+7/8+handlebars
     
  6. kshansen

    kshansen XS400 Addict

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    One mostly working way to tell what is causing the problem. Open the bleeder on the caliper. If the drag goes away the problem is between the caliper and the master. If there is no change in the drag problem is the caliper, either piston hanging up or the sliders if it is a single piston caliper that is mounted solid.

    Note that with many disc brakes there is a little drag when released, not enough to make the bike hard to push by hand but enough to feel when turning wheel by hand.
     
  7. Excess Impulse

    Excess Impulse XS400 Addict

    Thought I would post an update. Previously that was the case, when i held the brake and cracked the bleeder, no air but only fluid came out, then the brake released. As soon as I applied the brake again it started dragging again. The sliders are all clean and move freely. I received my new HEL brake line in the mail but not the new master cylinder yet. I thought I would go ahead and try the new line to see if that was the issue. To be thorough I removed the caliper and was going to disassemble again to make sure no debris was in it. I could not get the piston to come out of the bore even with blowing air in it. So I removed the bleeder screw and banjo bolt and blew air through it to get anything out. Previously I have put new seals in the caliper and everything was squeaky clean before rebuilding. The piston moved freely. I reassembled everything and put on the new brake line and bled it out. I still have the same issue of the brake does not release. I do get the tiny bubbles in the master cylinder reservoir when squeezing and releasing the brake lever. Unless the problem is the newly rebuilt and very simple master cylinder, I'm at a loss for what the problem is. What makes the piston retract after applying the brake? Is it just suction from the little piston in the master returning? I can't even get the brake to stop dragging now when I crack the bleeder. I'm totally frustrated as I have done so much to this bike and the only thing stopping me from riding it is the thing that stops me! I'm at a loss for what to do if it's not the master cylinder.
     
  8. Excess Impulse

    Excess Impulse XS400 Addict

    BTW this is a 1980 SOHC and single disk.
     
  9. kshansen

    kshansen XS400 Addict

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    To answer you question about what retracts the piston when you release the brake, well for the most part nothing. That is except the little bit of tension on the seal in the caliper. That is one of the "good things" about disc brakes they are more or less automatically self adjusting. The only thing else might be a little nudge by the disc.

    It can be hard to say 100% sure without being there but if the brake does not release even when bleeder is open I would be checking the caliper, piston and seals. Next would the the mounting pins and such. I know you said you did but by opening the bleeder and or removing the hose those are about the only things left.

    As I have said before there will be a slight drag with brake released but should not be enough to really notice rolling bike by hand.

    If anyone else can add to or correct something I'm say please don't hesitate I won't stomp my feet and pout, well not for long!:boxing:
     
  10. Excess Impulse

    Excess Impulse XS400 Addict

    I thank you for your reply, though the drag on the brake is more than slight, it is noticeably harder to turn wheel and if ridden I can smell it burning and it gets hot.So until I get this resolved I'm not riding it. I have been researching the cause of what retracts the piston in the caliper and it seems to be the seal in the caliper moves slightly as piston goes outward clinging to the piston, and when the brake is released the seal wants to return to it's original position due to the elasticity of the rubber. I had been thinking there is some amount of suction when the master piston returns as the fluid that pushed the slave (caliper) piston out has to return to the master. But I don't believe there is a suction or at least not enough to pull the slave back in. I still suspect the master so I did remove it and will disassemble it and re-clean everything. I do have another master ordered but just want to figure this out. If it works I will just keep it for a spare. I was going to do the same for the caliper but struggled getting the piston out. If after cleaning (or replacing) the master and problem still exists I will revisit the caliper. Now as I say that I am thinking I should just tear it apart again anyways. I read the how to thread and followed what had been done and I did sand the rust off the piston with fine 600 grit paper, maybe I need a new piston. I did not put any type of lube on the new seal, just some brake fluid when I reassembled it. It did seem to move easily after reassembly.
     
  11. Jeff0133

    Jeff0133 XS400 Junkie Top Contributor

    When cleaning the MC, do not forget there are TWO holes in there, the main port for pushing fluid into the hose when applying pressure, AND the very small "vent" for returning fluid to the MC when releasing the brakes...I still feel like you have a vent issue
     
  12. Excess Impulse

    Excess Impulse XS400 Addict

    .
    Yes I was hoping to tear into it today and re-clean and check everything real good. That does make sense that the fluid cannot return so the pressure won't release. Just got an email saying my master was damaged in shipment, no more in stock, refund sent. Argh!:banghead: I will thoroughly clean the master and if needed repeat the process again for the caliper.
     
  13. Excess Impulse

    Excess Impulse XS400 Addict

    Caliper 2 piston.JPG caliper 3 piston.JPG caliper bore.JPG Caliper 2 piston.JPG caliper 3 piston.JPG caliper bore.JPG Thought pictures might help. I got the master apart and it was still clean. I don't think it's the culprit. I removed the brake line from the master and put my finger tip over the hole and when I squeeze the lever I feel pressure pushing out, and when I release the handle there is suction so the tiny return port is open. I removed the piston and maybe it is worse than I thought. I know it looks bad but the marks should all be below the place where the seal makes contact and they all feel smooth. Maybe I just need a new piston??? I have a 1974 TX650 which has a completely different master and caliper, was thinking of maybe seeing if that piston is better and would work. Caliper 2 piston.JPG caliper 3 piston.JPG caliper bore.JPG
     
  14. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    That piston is scrap metal. Replace it. While you are at it, carefully inspect the piston seal. Some are cut on an angle on the inner diameter (the surface that contacts the piston). If installed the wrong way, the piston won't retract properly. And as others have repeatedly suggested, carefully check the ports in the master cylinder.
     
  15. spectra

    spectra XS400 Junkie Top Contributor

    I agree with the above post.......mine looked kind of like that and well said for 60 bucks just get 2 new ones. I figure its the brakes don't second guess it and just replace a few items.
     
  16. Jeff0133

    Jeff0133 XS400 Junkie Top Contributor

    Looks pitted and I guess it would hang there...change it out.
     
  17. Excess Impulse

    Excess Impulse XS400 Addict

    https://hvccycle.net/yamaha-brake-caliper-pistons/
    I ordered a new piston from here. That has to be the issue. As mentioned in my last post I removed, disassembled, and cleaned the master cylinder and made sure the tiny port is open. This seems to be confirmed to me as I can put my finger tip over the hole for the brake line and pull the brake lever and feel pressure, and when the brake lever is released, I feel suction. Master should be good.I have a new HEL brake line, and a new piston has been ordered. 16VTGI Dave you mentioned checking the inner caliper seal to see if its cut on an angle and could be installed wrong. Is it supposed to be cut with an angle on the side that contacts piston? Just looked at it ( it's brand new) and it is cut square on both surfaces.
     
  18. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    The pitted piston is ONE of the issues. There should be no suction generated by the master cylinder. The brake leaver is either adjusted wrong (must have free play, check the manual), or the passages in the master are not clear.

    Some callipers use a seal that is angle cut (slightly) to help retract the piston, others don't. Not to worry if the seal is square cut. The flexing of the seal when under pressure is what retracts the piston a fraction of a mm back when the pressure is released.
     
  19. super_usdm

    super_usdm XS400 Member

    I just got done dealing with this same issue and it turned out to be a clogged relief hole on the MC. I would double check that. To clear mine I cut away the plastic tab covering the forward divot in the MC reservoir and then used a safety pin and vice grips to poke into the hole. There is a tiny little hole that goes into the MC bore in the middle of the hole under the plastic tab you can cut off.
     
  20. Scorpio1963

    Scorpio1963 XS400 Guru Top Contributor

    Dealing with the same issue so your thread is helpful for me.I will be checking all things mentioned above.Thanks
     

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