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Thumb operated rear brake options for the track

Discussion in 'Technical Help' started by Android853sp, Dec 3, 2013.

  1. Thats the one that got me thinking of making my own . I have started this afternoon but it will take a while . The brembo one I have would work but its a bit big and as Mary Hinge has said it will have to be powerful . The internals of the brembo I have is only 10 mm so im going to make a 14mm bore one very similar to your picture . Need to sorce some high pressure seals as well .Dont think making it dual would be possible as the pressure would return to the other reservoir and I dont know a way round that.
     
  2. Fitted a thumb brake on my Zx10 a few years ago and didn't get on with it. I used to do at least two or three Ring trips a year so it wasn't a dedicated track bike and had to be road legal, no problems re the Mot. Made the mistake of taking off the brake pedal instead of fitting a splitter so every time I tried to fish out the ticket for the barrier the bike would roll forward. So had to keep one hand on the bars whilst sorting the ticket etc, its surprising how much you miss a traditional brake pedal until you've removed it.
     
  3. GP tech do a junction valve, basically a special banjo bolt that allows the use of both foot and thumb brake. Again, it comes at a price, $55. I've not looked for a UK supplier yet. I've got to admit I wouldn't want to lose the pedal so originally i was looking at the AP twin circuit brake caliper but, well, basically, i'm too poor.

    If i remember correctly Harris used to make a neat small rear MC too.
     
  4. Ive roughed out my master cylinder . Looks easy enough to make but this is my first so I could be wrong . Piston is going to be next before finishing in case I cant get it to work.

    photo.JPG
     
  5. How are you going to hone the bore?
     
  6. 1037 sps thanks.
    Junction valve . I will look into that . It seems that all that is needed is to remove the reservoir from the foot brake and fit the thumb brake in its spot. Might be easier than I first thought.
     
  7. final edition.

    I cut it with a 14mm end mill so the finish is very smooth already but I have reamers that would fit if necessary . Theres a spring that pushes the piston back so it would only need the first 70% honed as the seal doesn't go any further.
     
    #27 ducati2242, Dec 13, 2013
    Last edited: Dec 13, 2013
  8. Being smooth will cause a problem, as it won't seal properly. Think of it similar to your cylinder bores.
     
  9. Its only a rubber O ring type piston . smooth bore will be fine .

    IMG_3122.jpg
     
  10. Get a piece of 1/4" round bar a foot long, cut a slot 1" long along the diameter of one end, fold a piece of 600 wet/dry sand paper in 1/2 and slot it in there, put a drill on the other end, and hone away to your hearts content, using brake fluid as a lubricant, job done :upyeah: (don't over do it tho', it won't take long to leave a good cross hatch pattern).
     
  11. Getting closer .

    thumb brake 5.jpg
     
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  12. Looking good. How did you work out where to put the pivot point of the lever?
    This is what I was thinking while considering to build one. Obviously you don't want it too stiff to push, or so soft you have to push half your hand under the bar to get it work.
    Or did you just look at others and just take a guess?
     
  13. I guessed . I put the bracket around the fork leg and worked out where the master cylinder would have to be ,for clearance , then I cut the lever , Positioned it according to where your thumb would be , and that was the pivot point . Trial and error will tell if its in the right position but its only a new lever if its wrong. I have ordered the 14 mm rubbers for the cylinder so untill it comes I cant get on with it . I may end up sleeving the homemade cylinder with stainless tube if I have any leaks through back pressure.
    I have researched the junction valve that you told me of and found that it is in fact only a fitting to fit the brake line to the reservoir of the foot cylinder so I am going to take out the reservoir and sleeve and tap the cylinder to take a banjo bolt and fit the hose directly to it. I may have to open up the hole into said cylinder but will try it first .
    Going to 14 mm on the cylinder was also a thought on reducing thumb pressure . They are a common size so rubbers are readily available .
     
    #33 ducati2242, Dec 15, 2013
    Last edited: Dec 15, 2013
  14. Here it is nearly finished pressure tested and no leeks . Just deciding whether to paint it satin black or not . Will need lacquering if no paint .

    IMG_2397.jpg

    IMG_2400.jpg
     
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  15. Well its on . I had to re configure the lever so as to get the master cylinder far enough away from the head light/clock surround but it works . As said by Mary Hinge it needs a good push to get it to work . I made my own junction valve that fits into the oil reservoir of the lower brembo rear brake. I drilled out the feed hole into said brembo to 1 mm as it is only .5 mm but I'm thinking that maybe it needs to be bigger still I will try it at 2.5mm and see if there is a difference . Will also get some fitted photos.
     
  16. Here it is . Needs to be finished but everything is working as well as I expected . The hole in the bottom rear master cylinder is now at 2mm and I can get good pressure . I tried it bigger , just as well I have spares , but the rubber piston in the master cylinder tore on the enlarged hole . I will take it off at a later date after a few trials for polishing and anodising . One thing though, for anyone thinking of one, Its a tight fit . I needed a lot of equipment to make it work . Lathe , Milling machine , AC/DC Welder and a good supply of stainless and alloy materials .

    thumb brake fitted 1 copy.jpg

    thumb brake fitted copy.jpg
     
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