Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: iansoady on April 29, 2022, 09:19:53 AM
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As I mentioned elsewhere the front brake on the little Honda is very wooden feeling with barely any travel. The standard master cylinder is 5/8" diameter - or so it says on it....
I had a similar problem with the Guzzi V50 and fitted a master cylinder from a Honda model but have mislaid the information I used at the time. I'm looking for one either 11mm (preferred) or 12mm bore with a 10mm mirror mount. Does anyone know where I can find out what might be a suitable replacement?
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Hi Ian
I just measured the spare master cylinder from my old CBF500 and that is 15mm which I know is too big for your needs, but it wasn't that bad in use on my GN250. It certainly made that brake feel less wooden.
Spartacian
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Thanks for that - it does depend on the caliper piston diameter as well. I'm trawling through ebay listings for repair kits which usually give the diameter so I can refer back to the actual master cylinders. It seems CBR250RR and CBR125RR master cylinders are 11mm and there are quite a few available as well as cheap aftermarket ones which of course are an unknown quantity.
I'm also not entirely sure I've got the existing bore correct as it says 5/8 on the casting which I make 16mm so 11mm would be too small. 12.5mm or 1/2" would be better. Of course what is fitted may not be what it left the factory with.
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I've got a 1/2" diameter master cylinder which is from a CBR500. I am however slightly concerned - the lever action is very much improved but travel is much greater. I did expect this but it's more than I thought - explained in part by the fact that the lever pivot to actuating point distance is substantially less than on the original (around 20mm as opposed to 25mm or so) so multiplying the mechanical / hydraulic advantage. It down't quite come back to the twistgrip but not far off.
There may still be a small amount of air in the system although I've bled it carefully so will leave to rest for a while.
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After much toing and froing have ended up with an ebay Chinese special https://www.ebay.co.uk/itm/313949787916. This has a 14mm bore but 20mm pivot to abutment distance. For various reasons have only just managed to try it. The feel is much better than the original but not as soft as the last one I tried.
A brisk 20 miles showed me that the front brake is much improved both in feel and effectiveness but still needs a substantial handful to get a decent effect. All in all the mod seems to have been worthwhile and I enjoyed the ride very much.
Just one point about the ebay item - although it was listed as being located in the UK it actually took around 10 days to arrive and clearly came from China, so not one to use if you're in a hurry.
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Hi Ian
That's good news and thank you for the information it is helpful. I have often wondered about the Chinese brake master cylinders on eBay as the original on the Mighty Midget is sloped for cruiser type bars so sits at a strange angle. I had to take the CBF500 one off as the piston jammed one day and wasn't returning properly.
Glad the Honda is still a source of fun.
Spartacian.
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Having said all that I do wonder about the pads which look pretty new but I have no idea what make they are. I want maximum retardation rather than fade resistance, not being in the habit of using them that hard. What would people recommen? EBC organic?
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I've now fitted some EBC Kevlar pads (NOS) which now they've bedded in, are working very well. I now have a front brake that stops me reasonable well and has good feel. It has taken a while.....
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Having some issues with my RS front brake Ian and recalled this thread. Is everything still working OK on your RS front brake?
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Yes, haven't used the little Honda that much but the front brake is infinitely better than it was.
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Thanks for reply Ian. Have just ordered the same one as your's . I serviced the caliper 12 months ago but the master is playing up now.
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Hi Ian. Master has arrived but the mirror thread is smaller than the mirror I have. Did you need an adaptor to fit your mirror? Thanks.
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I have home made mirror extenders so just used an 8mm bolt with a sleeve in the extender on mine. I did forget to mention that!
Yours seems to have arrived much faster than mine did.
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Thanks Ian. Yes I think mine has arrived in less than a week.
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Have just ordered an adaptor off a well known internet auction site.
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Fitted the new master today and all is well. Got to go for a test ride but the action already feels loads better and the brake light switch is now not sticking on. Dead easy to fit as well. Just a straight swap and no need to bleed as the pressure came straight up on the lever as I filled the master and gently pumped away.
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Good news Martin. A few years ago I would have avoided Chinese made bits but these days they seem much better quality although there are exceptions.
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Yes agreed Ian. The quality is very variable but if you can get a personal recommendation then at the price it's worth a punt.
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Now road tested and works great ;D