Very poor rear brake

Discussion in 'Mechanics Garage' started by daffyduck1962, Feb 25, 2018.

  1. daffyduck1962

    daffyduck1962 New Member

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    My 2001 VFR800 has always had a very shoddy rear brake. (Had 10k on the clock when I bought it and is now just under 21k) If you want it to hold you stationary on a hill it will do that, but once the wheels are turning it would be more effective to use the soles of my boots!
    So I decided to convert to a delinked system with Hel brake lines. It took me all weekend with a the help of a friend. Very involve dwhen it comes to removing all the link pipes.

    Anyway the job is finished and the bike is back to it's original glory, so I took it down the road to test the brakes. Front brakes are great, as they always have been, but the back is exactly the same!!!!!!!!!
    Plenty of pressure, very little movement in the pedal under foot, but it doesn't slow the bike down any better than before. Rear wheel spins freely when brake released.
    I'm guessing there must be a problem with either the rear pistons in the caliper or the rear master cyclinder.
    But how do I identify which area to start checking first?

    I had always intended to delink the brakes as I thought it was an over complicated system when it came t bleeding the brakes with so many bleed nipples.

    The new set up involves a double banjo on the front master cylinder, and a single line to each of the outer piston feeds.
    The rear also uses a double banjo and two lines back to both feeds on the rear caliper.
    This system is the same as that which is used on the Blackbird, and I spoke to John (he used to run Jaws Motorcycles), and he talked me through it before I began.
    Any ideas, anyone?
     
  2. Darth Vader

    Darth Vader New Member

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    I put a cbr600 rear master on mine, just bolted on and made a world of difference. EBay a tenner.
     
  3. squirrelman

    squirrelman Member

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    could be a bleeding issue.....
     
  4. daffyduck1962

    daffyduck1962 New Member

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    Right, I've stripped the rear caliper apart yesterday, and checked the condition of the following parts:-

    Pistons - very good,clean no burrs, scratches. slide inside the chambers.

    Piston seals - intact

    Slide pins - cleaned and a light covering of copper slip grease applied. No burrs or rough edges.

    Rubber boots - intact, no splits.

    The spring retainer clip which sits over the pads was slightly bent. straightened out.

    There was a collection of oil around where the spring pad clip sits which I think must have come from the scottoiler. Cleaned.

    Pads appeared glazed slightly, so roughed them up with a metal file.

    Cleaned anti squeal shims.

    Caliper body cleaned.

    Caliper rebuilt, Hel lines reattached,and system bled. Firm pedal, brakes not binding.


    Went for a test ride.

    Result,slight improvement but it's never going to lock the back wheel up!!!!


    Could it be the pads; master cylinder or disc?

    Stumped, and pissed off.
     
  5. fink

    fink Member

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    Most wont. You don’t feel the effect of a back brake as you do the front.
     
  6. Allyance

    Allyance Insider

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    I think that the diameter of master cylinder in relation to the pistons is probably the problem, not enough mechanical advantage. I have locked up my rear tire on my '83 no problem (unintentionally). If the CBR600 is bigger then that is your answer, don't know where you can find the specs on master cylinders other than trial and error.
     
  7. mello dude

    mello dude Administrator

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    ^^^^ This... the stock m/c wont do it, you need a 14mm dia.... RC51/F4i/CBR600/SH .. all have 14mm.. buy any and retrofit.... - I just purchase a new RC51 and added to mine.
     
  8. OOTV

    OOTV Insider

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    Not sure of what size the CBR929 MC is but I have a rear MC and brake caliper if you are looking for something different.
     
  9. VFR4Lee

    VFR4Lee Member

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    Back brake sucks.
    For a second there I thought I was looking at the Aprilia forum. Or Ducati. :Pound:
     
  10. Allyance

    Allyance Insider

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    My ‘83 doesn’t have ABS and I don’t ride it very often, but the ‘14 does. One day a guy starts to pull out in front of me from the right on the ‘83 and I instinctively jumped on the brakes like I do on the 8th gen, rear wheel locked up and started to slide out to right! Now I have to remember not to do that again!
     
  11. scottbott

    scottbott Member

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    something similar happened to me and I locked my rear probably looked quite good from behind as the rear came around a bit luckily I was going slow it left a nice 'darkie' on the road though!
     
  12. OZ VFR

    OZ VFR Member

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    Yes, your rear master is too big for the caliper with three pistons if you've delinked them.
    You've gone from two rear and two front pistons being operated by the rear master, to three pistons.
    Best option are CBR600 or CBR250RR rear master, more or less a straight swap.
    All Honda master cylinders have the size stamped on the side.
     
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