Braking problem, need help/suggestions please

Discussion in 'General Tech Talk' started by The Kiwi, Dec 28, 2017.

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  1. The Kiwi

    The KiwiSupercharged

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    Front brake lever has lost pressure, brakes still operating safely, but the lever comes within 6mm of hand grip. The system has been bled and reservoir topped up. Pumping brakes doesn't help.

    Thank you,
    Mal the Kiwi.
     
  2. barbagris

    barbagrisMad Scientist

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    Replace Master Cylinder seals.

    Original hoses? - If so the T union is a bubble trap and if there is one in there - Flush Bleeding alone MAY not shift it. I have seen this in all sorts of bikes.
     
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  3. ozrider

    ozrider2008 Standard

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    Hey Mal, @The Kiwi ..... Ive had a similar issue, I ended up gently pushing back one brake pad so the pistons are right back, pumping the lever till they are back out...... then the next one etc.
    the seals tend to hold the pistons back
     
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  4. Mike Rocket

    Mike RocketRocket 3

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    Same thing happened on my Road King, front brake lever almost touched the handle bars. I changed the fluid and bled them out but it was still the same. I ended up removing the front brake calipers, removing the pads, pumping out the pistons as far as I dare without popping them out and cleaning all the dried brake dust and crud off them with brake cleaner then made sure they moved freely in and out ok. I done the same with the back plate of the pads and cleaned the edges, put a film of copper slip on the pad back plates and put it back together. Job was good and brake lever back to normal. It seem the slight corrosion on the pads was not letting the pads come out squarely and was slightly twisting in the caliper.
     
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  5. stollydriver

    stollydriverLive life to the full

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    Make sure you change brake fluid, if previously over heated - moisture build up etc, this can give similar symptoms.
     
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  6. Bedifferent

    BedifferentOld man on a bike

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    A little off topic....I haven't had this problem with my bike, but I have noticed a issue ever since it was new. Every time I give a hard squeeze on the front brake lever it kind of gives way about a half an inch suddenly. It only seems to occur on the first squeeze. It never gets any where close to bottoming out and it's only on that first squeeze. The brakes always work fine even with that little quirk. I have chosen to ignore it because my braking never seems to be compromised. It's hard to describe it. It almost like a catch or something breaking loose.
     
  7. albertaduke

    albertadukeformer airline pilot without the big bucks

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    if this is so what remedy do you suggest as I just bled all brakes and the front has that mushy feel and I gently tapped all the lines and pads to dislodge any air bubbles among other things short of buying a vibrator to shake the bubbles free
     
  8. barbagris

    barbagrisMad Scientist

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    I have a simple methodology - BUT it is time consuming and occasionally frustrating. And may need a photo. Give me a moment.
    But imagine you are the bubble and do not want to come out. Where would you hide. On an R3 it is that 3 way union and where the hose affixes to the M/Cylinder.
    I have seen poorly made Banjo bolts that have a pocket too. The hose (unless it's like the rear one @Paul Bryant had) is very unlikely.
     
  9. barbagris

    barbagrisMad Scientist

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    @albertaduke

    OK

    I needed a coffee and to collect thoughts.

    This is all trial and error experience - And I have bled "unbleedable" bikes thus. It also works on Combined Braking Systems (like old Guzzis)- I've never had a bike with ABS so cannot say.

    Some of the old tricks spouted on the "never wrong" internet are correct for rubber hoses - but R3's come with PTFE lined hoses and so they do not always work.
    I have fitted PTFE hoses since the early 80's on ALL my bikes pretty much from day one.

    In damp climates I also PREFER silicone based DOT5 fluids. There will be nay-sayers, I have 35 years-plus of ignoring them.
    I have many reasons, but mainly (now) because I have proven most of them WRONG.

    The key to "home bleeding" is to make sure that any bubbles (and there are ALWAYS bubbles) will rise all the way to the fluid reservoir uninhibited.

    Bubbles are crafty buggers and will stick to any anomaly in the circuit that affords them traction. This can be dirt or a mark in the tube liner surface.
    But PTFE hoses generally have a nice smooth inner face. I have seen an issue where the hose inners were marked in the extrusion process - but it is RARE.

    99% of bikes have handlebar grips that are lower at the end than where the hose junction is.

    In general therefore - I have found that by having the bike on it's side stand and on full left lock the fluid reservoir is at the top of the circuit and that bubbles rising from the left disc do not try and go into the right disk circuit. Rears are occasionally more tricky but the upwards route is key.

    Step 1 is to bleed as you would normally. Work from the bottom upwards. I ALWAYS use the bleed screws AND do a banjo bolt bleed - very lightly loosen the banjo and force liquid out (air and shyte can and will collect in the banjo grooves) - the advantage here of DOT5 is is it is not damaging to finishes (like paint). But timely application of a paper towel is equally as good.

    Double Banjos are a serious bubble magnet.

    If Step one works - all is good with the world. But step 2 & maybe 3 will get your levers rock hard (if you so wish).

    Step 2 requires patience. And if you have anything like Barkbusters fitted - remove them. Remove reservoir top. With the palm of your hand on the ball end of the lever (or toe of foot lever) very slowly push the lever until you see a small pulse of disturbance in the fluid. This marks the point at which the system pressurises. On some bikes you can actually just feel this - but on most you need to see it.

    Pump the lever VERY fast 4 or 5 times using your palm and release (slowly) - you almost certainly will get a back rush of fluid - have a rag ready. Wait a bit - now very slowly push the lever back to that system pressure point - this will almost always result in a whoosh of bubbles.

    Just repeat until (usually quite suddenly) the lever is firm and no more bubbles exit.

    Step 3 is both an option and sometimes necessary on very recalcitrant systems - though usually ime due to shyte trapping some bubbles. You pump and then keep the lever depressed a goodly while - often you'll see "tied back" quoted. My personal opinion is that if you need Step3 then you may well should be considering clean (new) components. After a while under pressure the bubbles usually dislodge and then exit with the slow pressure point purge.

    If Step 3 does not work 1st time - consider replacing parts - and tbh if you have to go down the rebuild route - rebuild everything.

    As some here know - I gift some of my free time each week at a mate's bike workshop. Despite them having vacuum bleeders and even a bottom up pressure bleeder, there are times when the above is still required.

    Now I know others will have their own methods. But this has NEVER failed me.
     
  10. Mike Rocket

    Mike RocketRocket 3

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    As I understand it, Silicone brake fluid is not recommended for abs brake systems for some reason, unless they have changed some spec on it now.
     
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