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Thread: Rear disc brake lacks bite

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    Default Rear disc brake lacks bite


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    Hi, I have a Honda Fireblade 900 of 1994 origin with a single sided swinging arm conversion from a vfr800 or 750 on it. Problem is that the rear caliper lacks any stopping power no matter how hard you stamp on the brake . I've stripped the caliper, replaced the pads, the braided hose and bled all air out. The brake lever is firm but still no bite to it( not enough to lock back wheel even if you stood on the brake )
    thought it may be to so with the vfr having linked brakes and. mine not? There is only one brake line input to the caliper, so hve doubts it is that . Help!!

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    Default Re: Rear disc brake lacks bite

    It's usually a vfr750 arm on that vintage blade, however they didn't use linked brakes until the vfr800. That arm is way harder to mount on your frame.

    Either way it'll be a mismatch between the size of the rear master cylinder and the size of the pistons (which are being used) in the rear caliper.

    From what you say where the pedal is firm but there's no power, you need a smaller master cylinder. The fireblade OEM master is 14mm. You can readily find 1/2" master cylinders of the same pattern from other hondas right up to the modern day. Check the mounting holes look same as your existing cylinder ofc. Newer is better as younger seals, doesn't matter what cc bike it's off.
    https://rover.ebay.com/rover/0/0/0?m...2F123808769654

    If you could read off the master cylinder bore size (probably 5/8 or 14) and measure the pistons which are in use on your caliper I can do a bit of maths to compare.

    A picture would also be handy. Depending which of the dual brake circuits you've hooked up, could be using one or two out of the 3 pistons. You want it on two if you've got it on one.
    Last edited by a_morti; 20-06-19 at 13:14.

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    Default Re: Rear disc brake lacks bite

    Thanks for the reply, I'll do some measurements and progress along your suggested route . Appreciated.

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    Default Re: Rear disc brake lacks bite

    So I got master cylinder from e bay from a Honda CBR 125 which is a 1/2'' one to replace my 5/8'' one, and it is an exact fit replacement, just needed the threaded holes drilling through and the Fireblade ones screw to the frame. Bled it all though and ....will give it a run in the morning and let you know!!!

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    Default Re: Rear disc brake lacks bite

    I may have been wrong about OEM being 14, but I guess there's no way to be sure now whether your bike had a CBR or vfr master.

    If it's gone too far the other way (long pedal throw, spongey feel), a 14mm cylinder will solve it.
    Last edited by a_morti; 30-06-19 at 11:21.

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    Default Re: Rear disc brake lacks bite

    Braking much improved , can actually feel it working now. although it is slightly spongy as you say I'll probably keep it as it does provide a bit of feel and isn't aggressive. Looking on eBay it appears that the 1/2 inch one I have is the same as the OEM for a VFR 750 so it should be matched to my. caliper. I may for interest try a 14mm as that would be midway as you say. Anyway, happy for now , thanks a lot for your help a_morti

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    Default Re: Rear disc brake lacks bite

    The master may match the caliper, however on a rear brake the pivot point on the lever can be different too.

    In the end, close enough can be good enough on a rear brake. It may also just want a more thorough bleeding though. A lot of these custom bikes run the hose through the inside of the arm which looks great but isn't easy to bleed spot on.

    Happy to have helped

    Can we see the bike?

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    Default Re: Rear disc brake lacks bite

    Thankfully the master cylinder for a selection of Honda's are the same dimensions so the travel and lever position is good. It did take a while to bleed but it is not bad now. I'd like to post a picture but can't see how you do it !

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