Soft brake feel

Discussion in 'Maintenance' started by RR7, Apr 21, 2020.

  1. RR7

    RR7 New Member

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    Hi.
    Did a full rebuild of the brakes last year, but retained the original pads that were hardly worn. All seals, Hell lines and a thorough bleed.
    The rear was good immediately, but the fronts were soft and I could pull the lever nearly back to the bars. Tried the old 'tie the lever back overnight' trick and it improved things a lot but still not like I want it. Since then been ok but not great.
    Would you say a new set of pads would make much difference? the existing though old do stop if you pull.
    Also, I see some of you have the RCS19 master cylinder, I understand it has an adjustable lever ratio. Is the OEM master a weak point?
    Also too, would I need a matching clutch lever?
    I only ride the roads and I'm not a very quick guy tbh.
     
  2. raphael

    raphael Elite Member

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    Have a look at a new seal kit mate it must be something with doing if they’ve made a kit for them? I personally don’t think new pads will make that much difference as most of the stopping power comes from the master.
    Personally I would just go with the brembo, acassato or hel master as much better
     
  3. GappySmeg

    GappySmeg Well-Known Member

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    I've done the same (full re-build, braided lines, etc...) and found it didn't actually make huge amounts of difference.
    I have since replaced pads a couple of times, and this hasn't worked much.
    Everything I've read suggest that the OEM master is a weak point, but only in as much as it wears. You could service its seals quite easily and end up with more than enough stopping power... that's probably what I'm going to try next.

    (Although, a shiny Brembo RCS is very tempting...)
     
  4. Marc

    Marc Active Member

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    I've got an RR6 which I love but have never got on with the front brakes. Lever travels way too much for my liking and the stopping power is worse than the 20+ year old Thundercat I had previously.

    Similar to you I had new HEL lines, seals and pads put in. They weren't original pads, can't recall exactly what I went for now but they weren't cheap. Made no difference, brakes are still very poor IMO and the amount of lever travel scares me. RCS conversion is definitely on my to do list, have read a lot of positive reviews regarding the difference it makes.
     
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  5. Muffking

    Muffking God Like

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    Have you bled the master cylinder? It's hugely important if you haven't already.
     
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  6. Slick

    Slick Elite Member

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    Definitely start off with a bleed at the MC, but if the zip tie trick is bringing significant improvement it suggests that your pistons are being over retracted, check the obvious corroded pistons, build up of gunk behind seals, the wrong products may cause the seals to swell too.

    However having previously a RCS19 it would result in a much harder level with shorter travel, I would recommend any aftermarket over the OEM.
     
  7. RR7

    RR7 New Member

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    Thank you all.
    Yes I have bled the master several times and like the calipers it's got a new set of internals.
    I'm a bit disappointed that the OEM master is prone to wear, never knew that.
    Glad you confirmed my suspicions about new pads not being likely to improve things.
    All the new seals were Honda's own, and expensive. The pistons and all parts were spotless before reassembly.
    The 'tie the lever back' trick caught my attention as to why it works at all. It certainly does, at least for while, but any disturbance to the system seems to render it null. My theory is that the sustained pressure causes sealing parts to settle more firmly into the registers in the calipers.
    I assume I'd need two new levers with a replacement master?
     
  8. Grooveski

    Grooveski Active Member

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    Waved a rule at my RR5 to get you some numbers.
    Lever end travel with the RCS and braided lines is 30mm with the 20mm pivot length and 35mm with the 18mm. I run it on the 20mm pivot.
    [Edit - Measured at the outer edge of the twistgrip rubber - standard levers are longer than the one on the RCS]

    30mm travel seems to be my sweet spot. On the wee ZXR(which had less piston area) it was about 25mm and 30mm and I ran the 18mm pivot.

    The RCS comes with a lever fitted so all you need is a black dog-leg clutch lever that's a decent visual match.
     
    #8 Grooveski, Apr 22, 2020
    Last edited: Apr 22, 2020
  9. RR7

    RR7 New Member

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    Thanks again, however...
    I had a look at how the RCS worked and it occurred to me I could do the same operation on the OEM cylinder. Correct me if I'm wrong, but I believe the RCS works by preloading the system. It moves the piston slightly inward in the cylinder, on the higher setting, to produce a quicker feel at the lever.
    The OEM set up has a push rod between the lever and the piston. So I cut some round bar of the same diameter as the rod and fitted it into the lever's pocket, where the rod locates. On reassembly it forces the piston into the cylinder a little in order to refit the lever's pivot bolt.
    Result? The lever is as quick acting as you wish. A 1.5mm long part produced a better but not perfect lever, and 3mm long was too far, and had increased pad drag.
    As a permanent mod I may drill and tap the end of the push rod to take an M3 button headed screw, that could be moved to fine tune out the extra lever travel.
    What you all think?
     
  10. Grooveski

    Grooveski Active Member

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    The RCS adjuster changes the distance from the lever pivot bolt to the plunger, like so:

    [​IMG]

    The 18mm setting takes less force and more lever travel - the 20mm setting more force and less travel...
    ...to achieve the same same system pressure.
    Reduced lever travel with the RCS mainly comes from the increase in piston diameter from 17.5mm(OEM m/c) to 19mm. The adjuster is more for fine-tuning.

    What you're suggesting is the equivalent of holding the lever back slightly.
    First problem with that is that you're basically dragging the brakes and have possibly closed off the reservoir link and created a closed system. This is the issue that some folk have had with cheap chinese levers - the plunger hole isn't deep enough.
    The brakes drag a little causing the calipers to heat up, increasing the fluid pressure.
    ...which drags the brakes more, which heats the calipers more, which increases the pressure more...
    Next thing you know the brakes are ON outwith your control and you're in a whole world of smeg.

    Another problem with preloading the plunger is again related to the piston having to return to it's fully out position in order to open the feed from the reservoir. If this wasn't happening then as the pads wear the pressure in the system would decrease and the lever would come closer and closer to the bar until you had no brakes at all.
    Wouldn't happen quickly. It'd be over time and would doubtless be noticed before becoming a problem. Still - bad juju.

    Easiest way to check if what you've done is safe would be to whip off a caliper and make sure you can still push back the pistons.
     
    #10 Grooveski, Apr 23, 2020
    Last edited: Apr 23, 2020
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  11. RR7

    RR7 New Member

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    Greatvalal
    Great thinking, thanks.
    I'd watched a vid of the RCS and obviously got the wrong idea about how it worked.
    A bigger cylinder diameter like the RCS has is the best answer, you're right.
    So the RCS actually moves the cylinder relative to the pivot point?
     
  12. Grooveski

    Grooveski Active Member

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    The cylinder itself stays where it is, it's the hole on the lever(where you've been putting your spacers) that you move by turning a footery little screw hidden inside the lever body.
     
  13. RR7

    RR7 New Member

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    Right, yes got it now.
    I see Nissin do a 19mm version of the 17.5mm OEM. Think I may get one and see how it goes.
     
  14. RR7

    RR7 New Member

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    Did a bit of a test to see how much lever travel is involved before the fill port is closed off, as Grooveski warned. It's no more than 5mm measured midway, so thanks very much for the warning about my daft idea !
    Anyway, I've tried the 'tie the lever back' trick again and it reduced the lever travel by about 30%.However, after an hour or so, and pumping the lever a bit, the poor travel problem returned.
    This problem has been there since the last caliper and master rebuild, and possibly always was, I cant remember. I'm confident the pistons are very smooth and I even polished them with Autosol. It seems it's the seals are pulling the pistons back.
    It's subjective, but I spun the wheel as hard as I could before and after tying the lever back, and the pads definitely dragged more for a while when the initial improvement happened. Once the lever travel problem returned the wheel spun noticeably longer, like before.
    I've got a Nissin 19mm master coming soon and will be very disappointed if things don't improve.
     
  15. RR7

    RR7 New Member

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    19mm master fitted and the lever is harder but the travel is still too much.
    Did the same test to find where the piston crossed the fill port and it's a lot further on the bigger cylinder.
    I think I will modify the push rod as described and see how it goes.
     
  16. RR7

    RR7 New Member

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    IMG_20200517_201142 (2).jpg IMG_20200518_142330 (2).jpg
     
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  17. RR7

    RR7 New Member

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    Jig to create an adjustable push rod.
     
  18. Grooveski

    Grooveski Active Member

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    Just out of curiosity - what kind of lever travel distance are you looking for?
    I've got it in my mind now that your previous bike was an old FZR or the likes. Something that had zero travel and needed tendons of steel. :)

    Personaly I always hated that sort of feel but know other folk who liked it. When I put together the front brake for project baby-flat-tracker(my old DT125MX with the front end and bodywork off a kwack Eliminator 125) I was surprised how many of my mates grabbed a handful and said it was too soft.
    ...and I had to say "Try it again with one finger". :)

    P.S. The system is the the Eliminator caliper, a braided hose and a 16mm OEM Brembo radial m/c off an R6.
     
  19. RR7

    RR7 New Member

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    following your excellent call 23/4, warning of a real risk of ending up with seized brakes, I decided to conduct some experiements.
    Hi, following your call warning I could seize my brakes, I decided to get to the bottom of this.
    I made a little rig so I could find how much lever travel was needed to close the compensation port in the cylinder. The shock was after testing 3no. Nissin OEM 17.5mm masters all were different. The worst needed 8mm more lever travel to close the port. I stripped them and measured the push rods, pistons and the lever pivot position, as best as I could. The parts are just not that accurate length wise, I guess that's what you pay for in a top end race part.
    Anyway, after the brake light switch has closed, I wanted the passive travel to be as small as possible, but with the compensation port not obstructed.
    The rig lets me prove the port is clear.
    I bought a 19mm Nissin replacement, which is a better fit for the outlet and brake light switch, and that needed 1.2mm increase in the push rod length. That's what the jig is for, to allow the drilling of the 5mm push rod to accept an M3 machine screw.
     
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  20. Grooveski

    Grooveski Active Member

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    Good on you for carrying out the investigation and fashioning a cure. :)

    Interesting stuff that, I'd heard folk say that OEM m/c's tended to be poor quality but to be honest the Nissin radials are such pretty units I'd presumed they were beyond such sloppy engineering.
    Just shows - you can't judge a book by its cover.
     

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