11/16 Bore Master Cylinder with a single Disc?

Discussion in 'Wheels' started by BuddyK, Aug 1, 2013.

  1. BuddyK

    BuddyK Member

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    I've working on putting an 18in custom front wheel :D on my '04 Electra Glide which has factory dual disc on the front with an 11/16 bore chrome master cylinder. I want to change it to a single disc with the new wheel so the wheel is not completly covered by rotors.

    HD list a 9/16 bore master cylinder for their bikes with a single front disc and the 11/16 is for dual disc. Can I use my 11/16 mc with a single disc or will it push the seals out of the caliper from to much pressure?? I just put the chrome conrtols on the bike about 10 months ago and hate to have to buy another 200.00 mc if I don't have too. I'm hoping I can just run a new line from the cylinder down to the single caliper and eliminate the distribution tee under the lower tree.

    Has anyone done this or know if this will work??
    Thanks!!
     
  2. Breeze3at

    Breeze3at Well-Known Member

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    Buddy; Somewhere in my computer, I have an article about this, but cannot find it right now. Reciting from memory (believe at your own risk); It is ok to use a single disc. on a dual disc master cyl., you might notice more sensitivity in lever, or decreased travel needed. It's not good to use dual discs on a single disc master cylinder because there won't be enough fluid volume to move the pistons enough. If I can find the article, I'll add it to this post.
     
  3. Breeze3at

    Breeze3at Well-Known Member

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    Here is the link I was looking for: Harley Street Glide or Road Glide Single Disk Conversion, How to do it!
    If you Google the subject, you will find any answer that you want to go with. :dknow
     
  4. Jack Klarich

    Jack Klarich Expert Member

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    Changing hydraulic ratios -
    Now that you know that, you can consider how changing the sizes of any of the pistons in the system will affect this relationship. Let's assume we've taken a standard braking system which works fine and for whatever reason, we are thinking of making the following changes.

    Bigger master cylinder
    If you increase the size of the master cylinder, you will actually be REDUCING the power of the brakes. Yes, with a bigger master cylinder, you will have to squeeze HARDER to get the same braking force at the calipers. This is because you are reducing the hydraulic advantage you have over the calipers. Crazy, right? Maybe but it's still a fact.

    So why would anyone do this? Well, you will also be reducing the amount of lever travel needed to move the same amount of fluid, so if you've got very strong hands, or are on a race track and want/need shorter lever travel, then you might find it advantageous. Also, some bikes (t595, 600srad for example) are fitted from stock with what might be considered too small of a master cylinder, giving over-long lever travel, so some people like to upsize it to give a firmer, less vague feel at the lever. However if your bike as stock has good feel, then going up a size can make the brakes feel "wooden", that is, like an on/off switch. This happens when pulling the lever gently doesn't do much due to reduced advantage, but then with a tiny amount of lever stroke, that you have to squeeze hard potentially without finesse, you can very suddenly lock the wheel.

    You'll be reducing the power of the master cylinder, so reducing the amount of flex generated through the system, as you'll now need to squeeze harder to flex the calipers than you probably can. This difference is often very noticeable while standing in the parking lot, but you won't necessarily feel this difference on the move, as if you're at that point of feeling flex from the brakes, you've probably already locked your front wheel.

    Smaller master cylinder
    If you decrease the master cylinder size, you actually GAIN in braking power due to the increased hydraulic advantage you gain. Brilliant, why don't we all do it?

    Well, because you also increase lever travel. In some cases it's so bad that the lever hits the bar, maybe trapping your fingers before you stop hard. This is a Bad Thing! In some case, where the brakes as standard are "wooden", fitting a smaller master cylinder can improve them massively (xj600s) but if the brakes are already fine, you may end up with them feeling vague or spongy, or trapping your fingers.

    You can sub bigger master for smaller calipers, or vice versa, and the principles will hold.
     
  5. BuddyK

    BuddyK Member

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    Thanks for the link and replies. I'm convienced that going to a 9/16 master cylinder is the way to go for the conversion.
     
  6. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    Not necessary Buddy, I'm running a single disc on my 03 E-Glide and have had no problems at all. I actually like the fact that it produces more pressure at the lever. Helps slow me down. I tend to twist the wrist heavily at times:D
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