Very strange brake problem today

Discussion in '5th Generation 1998-2001' started by GreginDenver, Feb 15, 2017.

  1. GreginDenver

    GreginDenver New Member

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    Yesterday I took my '99 VFR out for a long "shakedown" ride. I rode all afternoon, covered almost 100 miles. No problems with anything on the bike, everything working as it should.

    So based on that long ride I figured I'd gotten the bike back together 100% correct.

    But today I took it out again for a very short ride and everything was fine until I decided to experiment with bringing the bike to a stop using only the rear brake (I wanted to feel what the linked brakes felt like when you used only the rear brake pedal).

    After bringing the bike to a complete halt with only the rear brake I put the bike in 1st gear and started off down the street again. As the bike began to roll I noticed right away that it felt like the brakes were still holding. So I got off the throttle and pulled in the clutch, when I did this the bike braked to a halt without me even touching either the front or rear brake. Then I noticed that the front brake lever was rigid, it was solid, unmovable.

    I couldn't move the bike at all, it appeared to me that one or both of the front calipers were locked onto the rotors. I put the bike on its sidestand and got out an 8mm wrench and very gently cracked open each of the front caliper bleed valves. This caused the front brake lever to relax and function normally.

    I got back on the bike and rode it the short distance back to my home. Once I got there I rode the bike around the block trying to make the malfunction happen again but couldn't get it to do the front brake lock-up thing again.

    Any ideas what happened?
     
  2. John O

    John O New Member

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    Scary, huh? I had something like this happen on the freeway - burnt my finger on the scorching disc when I came to a stop! Although that was not a VFR, I think the advice is to replace your brake fluid for sure. There may be a chemical problem. It's good you're being careful about this.
     
  3. Terry Smith

    Terry Smith Member

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    I can't recall hearing anyone else report something like this. Certainly heard a number of occasions where the back centre piston locked on due to debris in the secondary master cylinder relief valve on the left fork.

    I have delinked my brakes so can't look at the parts now, but IIRC the SMC is fed fluid from the hand lever; AFAIK that is the only point of fluid connection between the back brake system and the front, so my gut says look for debris in the SMC that would allow system to pressurise the front brakes. I assume you'd also need to have something stopping the hand master from relieving pressure through the relief port.
     
  4. GreginDenver

    GreginDenver New Member

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    Okay, I took the VFR back out for more riding to try to diagnose the brake problem.

    The issue is definitely heat related.

    When I first start the bike up (from cold) and begin riding, the brakes work properly. But when the motorcycle reaches fully warmed up temperatures the front brake lever becomes rigid and the front calipers grab and hold the rotors.

    The bike has freshly cleaned and rebuilt calipers, new Spiegler brake lines and new brake fluid. I only refilled and bled the brakes a couple days ago.

    What I want to know is why are the brakes reacting to the motorcycle's normal heat?
     
  5. RVFR

    RVFR Member

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    Never heard this one. I mean I've heard of the brakes getting hot causing the issue due to stuck pots or pads, but the way you have it, it sounds like it's from the engine side of it, and from what I gather there's no relationship. So the simplest in me asks, how are the brake lines routed? Thinking here you went the way the stock ones went. It will be interesting to see what others have to say, and what come of this.
     
  6. mello dude

    mello dude Member

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    Check your front master cylinders --- many times before people have reported this and the answer was there was gunk in the MC blocking all fluid to return to normal. -- 2 cent armchair beer buzz guess....
     
  7. GreginDenver

    GreginDenver New Member

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    I'm thinking my brake-bleeding wasn't effective after I refilled the system and as a result I've still got air in the lines and it is expanding with the heat, causing my problem. Brake fluid is designed to behave properly at normal engine operating temperatures (it doesn't expand) but when air is heated it expands by a huge amount.

    I'm going to have to re-read the Brake Bleeding procedure in the Service Manual because I obviously didn't get it right the first time. There has to be air in there somewhere.

    But tomorrow I have to go out on a trip so I'll have to wait until Sunday or Monday before I can work on the VFR again.
     
  8. 34468 Randy

    34468 Randy Secret Insider

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    I am no brake specialist for sure but reason has me saying there is a blockage of some sort. You mentioned an air bubble in the so maybe that too. I think you plan to re= read and hopefully re bleed the lines is the best thing to try first, then go from there. Make sure the brake pad pistons are not gummed up.
     
  9. RVFR

    RVFR Member

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    I just cringe at reading that bleed process on these linked brakes, what a royal pain in the ass.
     
  10. NorcalBoy

    NorcalBoy Member

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    It really isn't that hard to bleed the system, unless following instructions isn't one of your strong points.
     
  11. RVFR

    RVFR Member

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    ^ smart ass ;)
     
  12. OOTV

    OOTV Member

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    I've done the brake bleed process more times than I can count, not only on my 5 & 6 gens but on several other members bikes as well. The process isn't so much hard but tedious due to the number of bleed points. Having a helper sure does make it a little easier and speed bleeders definitely helps if doing the job solo.

    Just to note that the front MC is not connected to the rear system, the center pistons are though. The front system only actuates the rear via the SMC on the left fork/caliper. The rear though, does trigger the center pistons of the left and right front calipers. If the front lever is what is locking up, it is most likely the front system that needs to be looked at. That's not to say, ignore the rear but rather start with the front system first. Most likely it's the return hole or air.
     
  13. OZ VFR

    OZ VFR Member

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    Check the small rod between front brake leaver and master cylinder, if it's installed in reverse it will not allow master cylinder to drain back into reservoir and heat expansion will apply force which in turn drags the front brake, which in turn applies pressure to the secondary master cylinder which applies the rear brake, long answer.
    It will fit in either way, but only works one way, stupid design.
    From memory it's big end to leaver, small end to front master cylinder piston.
     
  14. OOTV

    OOTV Member

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    That's interesting, never knew that. I take it you found this out first hand?
     
  15. GreginDenver

    GreginDenver New Member

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    Thanks, that will be the first thing I check when I get back home from this trip.

    Strange that they built it that way, this VFR is without a doubt the most complex and tightly packaged motorcycle I've owned. I love it, but it's not a simple piece of machinery.
     
  16. OZ VFR

    OZ VFR Member

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    Sure did, rebuilt my brakes (before I delinked them) and went for an early morning ride.
    There was no traffic, and I don't use a lot of brake in the twisty stuff, and the cool morning helped me get 100km away before I upped the pace.
    As soon as I did the brake lever sarted to feel funny, then the front started to drag pushing on the secondary master and rear brake locked solid.
    I had tools with me so I eased pressure via the bleed nipple, it lasted about 4 brake aplications before it did it again.
    By this time it was 36*C and I was using words that are kept for special occasions.
    No matter what order I used them in, the problem wouldn't go away.
    So I pulled everything apart on the side of the road and doubled the amount of special words together with throwing things.
    This must have done the trick, as I got exhausted and decided to use my brain instead.
    I could see down the front rerservoir that the piston wasn't going back enough to release pressure and refill, so I pulled the lever off, as soon as I did the piston whent all the way back and front/rear brake released.
    Then I saw the stupid design of the push rod and reversed it, all fixed.
    There should be a "kick an engineer of your choice to death day" once a year.
     
    Last edited: Feb 16, 2017
  17. Terry Smith

    Terry Smith Member

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    Can we also beat up the guy that positioned the thermostat in the 5 and 6G?


    Sent from my iPhone using Tapatalk
     
  18. slowbird

    slowbird Member

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    This is a scary problem. Makes me wanna de-link my bike.

    Wow. I had no idea the ends for the little pushrod are different sizes.
     
  19. ridervfr

    ridervfr Member

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    Interesting, i have rebuilt numerous brake systems. I always place things down on the bench as i take them apart in relation to how it comes apart. The piston (if i understood correctly, has a certain swirl finish that contacts the brake lever.) When i did beemer brakes i would always look at my notes for the sequence of bleed operations that would be followed with a computer hook up that cycled the brakes though the ecu. Crazy chit when you compare my old gen 3 brakes to the new stuff.
     
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