CB350/450/550/750 Front Disk Brakes On CB125s
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CB350/450/550/750 Front Disk Brakes On CB125s

This is a discussion on CB350/450/550/750 Front Disk Brakes On CB125s within the Technical forums, part of the Caferacer.net Forums category; Hello! I'm new here. I'm 16 and taking on a cafe build as a personal challenge. I have a 1976 Honda CB125s and I'm sure ...

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  1. #1
    Junior Member Noah Williams's Avatar
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    CB350/450/550/750 Front Disk Brakes On CB125s

    Hello! I'm new here. I'm 16 and taking on a cafe build as a personal challenge. I have a 1976 Honda CB125s and I'm sure many owners have the same problems of the brakes just not stopping while moving at speed from what I have read on other forums. After about two weeks of fiddling with the mechanical disk brakes, I am finally giving up and putting new brakes on the front. I was wondering if anybody has mounted the Hydraulic disk brakes from the larger bikes (CB350/450/550/750) on a CB125s or early CB200. Curious if there would be too much stopping power for such a little bike, and if they would be easy to put on (require much modification or not). Not afraid of modifying brakes it would just be easiest not to! I'm making it into a cafe racer, so I want to keep the old school look of the vintage brake system, but actually be able to stop . Thanks!

  2. #2
    Senior Member woodsman's Avatar
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    Honda rebel 250 caliper will work. You'll need to have an adapter plate made.

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    Senior Member TrialsRider's Avatar
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    Those brakes are pretty crap aren't they! I'm not even convinced they are any better then the little drum brake that preceded them.

    I can't help but wonder if the front brake from a modern Trials or Motocross bike wouldn't make an ideal upgrade for your bike. I'll see what I can find in the way of aftermarket upgrade kits that might be made to adapt to your little bike. Throw up a photo of your front hub if you can, I'm pretty sure your stock disc is to fat to use, but the bolt pattern size of the hub is what we would need to know. Give dimensions of the hub as best you can.

    Solana Beach :/ must be nice.

    "old school look of the vintage brake system" get that notion out of your head immediately, that's the whole problem with the brake you have! It represents ancient technology that was attempting to 'look' period 'modern'.
    Last edited by TrialsRider; 03-10-2017 at 05:47 PM.

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    Senior Member Geeto67's Avatar
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    The last year of the cb350 and most of the cb360s had a hydraulic disc brake and 33mm forks, as did the cx500. I think the cb125 may use 33m forks as well.
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  6. #5
    Senior Member woodsman's Avatar
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    Quote Originally Posted by Geeto67 View Post
    I think the cb125 may use 33m forks as well.
    I believe they are smaller, 27-28 maybe.

  7. #6
    Junior Member Noah Williams's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Those brakes are pretty crap aren't they! I'm not even convinced they are any better then the little drum brake that preceded them.

    I can't help but wonder if the front brake from a modern Trials or Motocross bike wouldn't make an ideal upgrade for your bike. I'll see what I can find in the way of aftermarket upgrade kits that might be made to adapt to your little bike. Throw up a photo of your front hub if you can, I'm pretty sure your stock disc is to fat to use, but the bolt pattern size of the hub is what we would need to know. Give dimensions of the hub as best you can.

    Solana Beach :/ must be nice.

    "old school look of the vintage brake system" get that notion out of your head immediately, that's the whole problem with the brake you have! It represents ancient technology that was attempting to 'look' period 'modern'.
    Thanks! It happens to be one of the weird ones with Four Bolts, and the rotor is 7mm thick (a monster of metal).

  8. #7
    Senior Member TrialsRider's Avatar
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    Actually 4 bolts is what I was expecting. That's the same as a lot of Trials bikes.
    Also found this:

    That front brake is an 2 pot AJP brake calliper exactly like you would find on a late 1990's trials bike, or on the rear wheel of some even newer ones, the disc looks to be aftermarket unit, probably not very expensive one either. 4 bolt discs are fairly common on dirt bikes but you would need to nail down the bolt circle diameter and the size of the clearance hole to cross-reference it with a bunch of bike models.

  9. #8
    Senior Member TrialsRider's Avatar
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    Personally; I would trace out the pattern of your brake disc onto a piece of paper, or take it off and take it to a bike scrap yard and look for hydraulic brake systems on dirt bikes that you might be able to adapt to your existing hub. You live in southern California, you Must have lots of sources to check out down there. The whole system will probably end up being lighter then just your existing disc and will probably give you about 4 times the brake power.

  10. #9
    Senior Member kenessex's Avatar
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    the problem will be in mounting a caliper. The CB125s used the same type of single piston pivoting caliper as the first Honda hydraulic systems, except it is even worse as it is cable operated, so a normal fixed or sliding caliper will need an adapter plate that is difficult to mount to the fork leg and have strength and line up. But, it can be done.
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  11. #10
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by kenessex View Post
    the problem will be in mounting a caliper. The CB125s used the same type of single piston pivoting caliper as the first Honda hydraulic systems, except it is even worse as it is cable operated, so a normal fixed or sliding caliper will need an adapter plate that is difficult to mount to the fork leg and have strength and line up. But, it can be done.
    True that Noah; this will probably be the most critical and difficult modification you will make to your motorcycle. When you are shopping for parts you need to understand the difference between the 2 most significant formats of brake calliper design:



    The brakes I was leading you towards employ a fixed calliper which work more effectively and is more simple to bracket as the brake calliper remains in line and centred on the brake disc at all time. Any brake calliper that has a live brake pad or piston on only one side of the calliper will tend to provide less effective brake force by comparison and needs to follow the disc as the pads wear. Pad wear on a sliding calliper brake is generally uneven by nature of its design where all of the brake force comes from one side and the other side needs to float relative to the disc.

    Holler if you don't completely understand that concept and how to visually recognize the difference between those 2 styles of disc brake.

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