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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!
 

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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'.
 

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Discussion Starter #6
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).
 

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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.
 

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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.
 

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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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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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You will want a twin piston sliding caliper. These have the pistons on the outside. A caliper with pistons either side will probably be too wide and foul your spokes.

Something like an EX250 caliper would probably work well, but you will need to make a mounting plate for it as suggested earlier.

Also you currently have a fixed disc, so you want a sliding caliper. If you run a fixed caliper, then you should run a floating disc.
 

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I know what you are suggesting there hillsy and you are possibly very correct, but if he can find an AJP brake system they are super narrow in even a 4 pot format, I can give accurate dimensions if needed. Really shouldn't be much of an issue for clearance. If it is a front brake disc it probably will be a floater, but if it comes off the rear of a dirt bike good chance it will be bolted up solid. His stock disc is extremely thick and has a deep dish shape, so a change of hub or adapter is going to be needed almost for sure.
Performance wise the two opposing pistons is worlds better then the 2 on one side, 4 pistons is way better performing then either and obviously it's going to be a challenge for a noob to source and finance a workable system. Hopefully he will garner some assistance from somebody local with some skills and machinery.

Regardless of what front brake upgrades he ends up with, I have concerns that better front brakes are going to reveal the need for other upgrades to suit, such as tires, forks, and steering head bearings (the ones in there now are almost certainly crap) eventually once he has the bike to the point of being capable of nose wheelies the frame might even exhibit some noticeable flex or fractures. It's a difficult thing to upgrade components on a really old scoot that was built with price as being the highest order of business, so I wish him luck and hope he ends up with something safe, ridable and enjoyable. Realistically he would probably save money and end up with a far better motorcycle if he saved up enough to buy a slightly used CBR125R (preferably 2011 or newer) which were made in vast numbers, feature a far more advanced design and sold at greatly discounted prices throughout North America.
 

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How can you ever have too much stopping power when it is regulated by your fingers? I've never seen brakes lock up from a small amount of pressure on the lever.
 

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How can you ever have too much stopping power when it is regulated by your fingers? I've never seen brakes lock up from a small amount of pressure on the lever.
Easy; if you mount a pair of twin 12" 4 pot brembos on the front of a 125cc motorcycle :/ you probably made the bike about 20 pounds heavier on the front wheel then it needs to be. Not a matter of two much brake or locking up, just a matter of excess weight relative to what is sensible for stopping a light bike that is incapable of tremendous speed.
 

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Easy; if you mount a pair of twin 12" 4 pot brembos on the front of a 125cc motorcycle :/ you probably made the bike about 20 pounds heavier on the front wheel then it needs to be. Not a matter of two much brake or locking up, just a matter of excess weight relative to what is sensible for stopping a light bike that is incapable of tremendous speed.
Since he was talking about "too much stopping power." I will stand by my accurate statement. your reply is out of context. He was referring to adding a single disc. I would be surprised if the rotor and caliper were any heavier than a larger drum brake set up. I would suspect it would be lighter.
 

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True that, so the answer to that particular question is No, all those brakes that he listed are still pretty shite.
Your saying all CB350/450/550/750 disc brakes are worse than a CB 175 drum brake, really? That must be why Honda went that route instead. Nobody said anything about 12" rotors and 4 pot calipers.
 

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I believe they are smaller, 27-28 maybe.
I believe they were 27mm on the CB125.
Check this list of bikes with 27mm forks. Find one you like with a disc brake and swap the new forks and wheel into the CB125 trees and you're done.
Here's a 79 Cb125 disc set up, direct swap:



Or with a nice set of boomerang Comstars from an 85 CB125s




Fork Diameter Make Model and Year

27 Honda MB5 (82)
27 Honda CR-60R (83)
27 Honda XR-70R (97-03)
27 Honda XL-70K (74-76), XL-75 (77-79), XR-75 (72, 74-78 )
27 Honda XL-80 (80-85)
27 Honda XR-80 (83-84)
27 Honda XR-80R (85-91, 93-03)
27 Honda CL90 (67)
27 Honda S90
27 Honda EZ-90 (91-95)
27 Honda ST-90 (73-75)
27 Honda CB-100K2 "Super Sport 100" (70-72)
27 Honda CL-100K2 "Scrambler 100" (72)
27 Honda CL-100S2.S3 "Scrambler 100 5HP (72-73)
27 Honda XL-100S (81-85)
27 Honda XR-100R (85-03)
27 Honda CT-110 (80-86)
27 Honda CB-125S (73-75)
27 Honda CB-125S (76-82)
27 Honda CB-125S (84-85)
27 Kawasaki KD-80A (75-76)
27 Suzuki TS-50L (78 )
27 Suzuki TM-75 L/M/A (74-76)
27 Suzuki TS-75 M/A/B "Colt" (75-77)
27 Suzuki RM-80 B (77)
27 Suzuki RM-80 C (78 )
27 Suzuki RV-90 L/M/A/B "Rover" (74-77)
27 Suzuki DS-100 C/N/T/X (78-81)
27 Suzuki TS-100 C/N (78-79)
27 Yamaha YSR-50 T/U/W/A/B/D (87-92)
27 Yamaha YZ-80 A/B/C/D/E/F (74-79)
27 Yamaha DT-100 D/E/F/G/H/J/K (77-83)
27 Yamaha MX-100 F/G/H/J/K (79-83)
27 Yamaha RT-100 A/D/E/F/G/H/J/K/L/M (90, 92-00)
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Your saying all CB350/450/550/750 disc brakes are worse than a CB 175 drum brake, really? That must be why Honda went that route instead. Nobody said anything about 12" rotors and 4 pot calipers.
CB175 drum brake :confused: Dude, what thread are you reading?

 
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