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

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.

kenessex said:

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.

Click to expand...

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.

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.

woodsman said:

I believe they are smaller, 27-28 maybe.

Click to expand...

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)
----------

o1marc said:

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.

Click to expand...

CB175 drum brake Dude, what thread are you reading?