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  1. #1

    Default 1973 bonnie needs front brake master cylinder

    I have a 73 bonnie that is slowly getting chopped. I need a front brake cause I'm not that bright. My original master cylinder is blown out. It has the original Lockheed brake. I saw Fab Kevin using a front master cylinder from a modern sport bike. Like I said I'm not that bright, can anyone help with info

  2. #2

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    With a single Lockheed caliper you need to be careful you get the ratio correct as too large and you will have a wooden feeling leaver and a brake that is liable lock up, too small and you will have the opposite effect, here is a chart that should help, i have twin Lockheeds on my Trident with a 19mm master cylinder which works well, but would be too big for a single caliper.


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    Quote Originally Posted by Tricky13 View Post
    With a single Lockheed caliper you need to be careful you get the ratio correct as too large and you will have a wooden feeling leaver and a brake that is liable lock up, too small and you will have the opposite effect, here is a chart that should help, i have twin Lockheeds on my Trident with a 19mm master cylinder which works well, but would be too big for a single caliper.

    Just to add to Tricky13's chart, you need to know what the 'sweet spot' ratio is;

    ...'the importance of master cylinder to wheel cylinder ratios.
    This critical ratio is of paramount importance in determining "feel". It has been my experience that there is a "sweet spot" in the range. I like ratios in the 27:1 range-2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the spectrum-firm.
    Ratios lower than 20:1 can result a feel so "wooden" as to have a toggle switch effect: nothing happens until the wheel locks..."
    http://www.vintagebrake.com/mastercylinder.htm

  4. #4

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    Yeah forgot where i downloaded that chart from so thanks for that, so forgot the further info on sweet spot, but as mentioned in that write up the disc size will also be a factor in getting the feel you want.

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    Norton specifically ( I was at a tech session with 2 former engineers and staff) said they thought TOO MUCH front brake would cause accidents so purposely detuned the original designs to keep people from doing stoppies (Original bore on a Norton Commando was 5/8th i think?? Sleeving to around /12" is a popular mod, but seen 14mm master cyls offered * Double check sizes I am winging it off the top of my head could be a embarrassing math mistake in there)
    But Triumph did much the same in their designs.

    While dated, its still an excellent reference standard today is Fred Puhns "Brake handbook" by HP books and doesnt get overly technical (No algorithms and only sporadic coefficient of friction formulas)
    Its setup mostly for Perf Auto apps, but is relevant and useful.

    I was reading a series of excellent articles on Mike "The Bike" Hailwood and his return to racing in the 1970s on Ducatis in ClassicBike Magazines recent issue, and at the time Compagnolo wheels and brembo twin pots were the std for top performance. Hailwood like many racers never touched the rear brakes, Totally front brakes and Engine Torque is std for racing.

    On the street that will get you killed or a wreck first time you skid the front on a diesel spill or Hipsters hair Pomade So, I start with rear brakes and ease into full stops with front brakes, I will never forget a large,, and I mean LARGE fat girl on a Sportster drunk at the Oyster run (Bandidos, Tres hombres,Outlaws) and she was hauling ass with a group of bikes and I could see her front wheel locking up and skidding on & off, she had no idea till the front end hit a bump and down she went hard. Slide on her tits and belly a surprising distance. One of those accidents it seems in slow motion you see coming and cant do anything but watch it unfold. We explained WHY she wrecked as she was befuddled but she was also in shock and drunk so who knows????

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    Meant to add that Stock Triumph parts for those years are heavy and not that great. Unless burdened by some weird Anglophile obsession or $$$ and using what you have on hand then there is little reason to use the stock parts (Brakes).

    Find a Asian or Italian bike that you like how the brakes work, and adapt as a matched system. Then its a simple case of fabbing lines for it (use the stock lines for a pattern and sample for braided stainless) and adapters to fit. On my Cafe CB SOHC/4 Honda I salvaged forks and swing arm as well as brakes off a late model Honda sport bike. Better brakes, better suspension as Hondas early bikes were crap.
    On my street tracker as well as cafe Triumphs using later model modern Triumph parts with full floating discs, calipers and master cyls. A friend in California did one I like on his "Cafe Espresso" Triumph, Used a asian bike spoked wheel hub, Italian drilled stainless rotors (Floating) and modern Triumph Calipers (I dint remember the Master cyl) but the modern Triumphs say "TRIUMPH" on the caliper so cool looking. I liked it so copied the idea but slightly different methods..

    Good brakes can never be over rated. Posers can talk all the shit they want, But a bike that goes FAST, Handles well, and STOPS when you need it to while looking good is a good goal to have.

  7. #7

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    I have recently been through the whole brake balancing scenario with trying to mix AP Lockheed calipers with modern Japanese and American master cylinders...took me a while to arrive at a usable combination, i have used older Japanese MC with Lockheed single calipers with good effect before, but this time with a twin Lockheed caliper setup i have had to go through several different sizes to come up with a front brake that i can actually use currently 19mm/3/4" MC and the pistons are from what i remember 48 or 50mm.

    The rear has been a complete nightmare single Lockheed caliper and the same assortment of different MCs and i have ended up using a Harley MC 3/4" but as this was the only one that gave a semblance of a brake i have ended up adding another caliper to the rear in an attempt to balance it all up.

    I also think that today's bikes are way to over braked on the front, seen so many you-tube bikes loose the front end when trying to brake hard and miss a car...do they not teach anyone to use a rear brake as well these days.

    Last edited by Tricky13; 07-24-2018 at 5:42 AM.

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    Quote Originally Posted by Cttexan609 View Post
    I have a 73 bonnie that is slowly getting chopped. I need a front brake cause I'm not that bright. My original master cylinder is blown out. It has the original Lockheed brake. I saw Fab Kevin using a front master cylinder from a modern sport bike. Like I said I'm not that bright, can anyone help with info
    Back in the late seventies and early eighties, I had a chopped '73 750 Triumph Tiger. I used a Honda 750 master cylinder, that I picked up at a junk yard, for my front disc brake. Worked well for me. It was a lot easier at the time to get a rebuild kit for it, than to buy an OEM replacement.

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    I also think that today's bikes are way to over braked on the front, seen so many you-tube bikes loose the front end when trying to brake hard and miss a car
    That's the dumbfuck clowns riding them, not the brakes. Youtube is full of idiots who'd improve motorcycling by dying before they can encourage stupidity. Motorcycles brutally punish the stupid. I like that.

    I taught MSF courses for the USAF and noted most riders refuse to SYSTEMATICALLY PRACTICE. They buy the bike and think they bought skill along with it. Modern brakes are wonderful. Weight transfer means rear brakes do very little in an emergency stop. Grabbing instead of gradually applying front brakes is asking for a washout or with good modern brakes, an endo. I don't volunteer for those outcomes.

    You can't have too much front brake available, but you can APPLY too much front brake.

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    And just so you don't panic, and lock up your brakes, keep at least a good distance between you and the car ahead of you. Some idiot cuts into your safety zone, don't try to block them. Its going to happen, and anything that you might do, could end up with a road rash / pizza event.

    I agree with Farmall. Best to gradually apply the rear brake, following with gradual application of the front brake. But, also, plan an exit strategy, one that will not take you into the oncoming traffic lane, to get around whatever obstacle it is that you are face with. Sometimes acceleration is the answer, rather than braking.

    Also, be sure to don your armor, a helmet, Levi's, leathers and combat boots have saved me from miles of road rash.

    I, also, when first mounting an unknown Cycle, go to a deserted road. There, I get it up to around 30mph, and lock up the rear brake. So I can get a feel how it will fishtail. But, that's me, I don't recommend this to inexperienced riders.

    I have been over the bars, three times. Surfed my cycle once when I hit an oil slick from a previous accident. Also, had a canvas shoe catch fire, when I had my feet up on the engine guard, and got too close to the exhaust pipe. Been damn lucky.

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    WTH?!
    Who are you trying to give riding lessons to?
    I don't think anyone is impressed.

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