CB125 1978 Brakes dilemma

[Drav]

Hey guys, I am doing up a cb125s cafe racer style, and I am in a dilemma over front brakes. I have the 1978 disc brake model, but there was no caliper or hanger arm with the bike. A new caliper and arm from Honda is way to much to be paying for such a crap brake, so I am going to look at the hydraulic options.

Are there any available calipers that will bolt on, like a cb350 or 400, or will I need to replace the front end to get something else to simply bolt on? Will the Kawa gpz 305 brakes bolt on for instance? I have the 1978 disc wheel.

Furthermore I have access to a 2 axis CNC mill that I know how to use, so am looking at making a hanger arm, and hanging something else off it. I imagine something like the GPZ or the CB350 front caliper would work here, but what about rear brakes from bigger bikes, like the VFR750. The reason I am asking is that they are single pot, and (mainly) because they are cheap and plentiful second hand. Is this a silly question because I will run into cylinder or cable problems, or is this worth thinking about?

Also, why did Honda make the cb series calipers with an adjustable hanger arm in the late 70s, when nowadays they are all solid bits of metal? Anything I need to know here for fabricating my own bracket?

Finally, what do you think is the easiest and cheapest option to get some half decent brakes on this bike?

Cheers!

[Kickstart]

Hi

Not sure you will find anything that will bolt straight on.

From memory the CB125S used a swinging caliper. Suspect it was easier and cheaper to knock these out than sliding calipers. The caliper sat on a 'vertical' pin around which it pivoted a bit when you used the brakes (ie, you pull the lever, the piston pushes out, the pad contacts the disks and pulled the caliper across so the pad on the other side is brought into contact with the disk).

If you have the right tools it might be possible to knock out an adapter to go from the standard fork to a more common hydraulic sliding caliper. Plenty of these calipers to choose from.

All the best

Keith
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[Drav]

Thanks Kickstart, going to get a GPZ 305 hydraulic front caliper and try and make a rigid hanger arm for it as you described. Will post some pics when I have a cardboard mockup to show

Cheers!

[Kickstart]

Hi

While it will do the job, I would be a bit dubious of that setup. For a start the GPz305 had twin disks so you probably need a smaller bore m/c to avoid having very dead feeling brakes. Also it is a smallish caliper.

On the other hand I can see why you are tempted as it keeps the style of the original caliper.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Drav]

Hmmm, good point about the twin setup and small size. Ive been told they will fit the slightly fatter Honda disc, and yes they are roughly the same shape as the originals, which are the two plus points. Have you got any other ideas for a suitable caliper?

If not, not to worry, I still dont think a GPZ305 caliper could be any worse the the original front brake!

[Kickstart]

Hi

Most I can think of are twin piston sliding calipers.

Not sure if something like a single caliper from a GPZ900R would fit and if they are a little more up to the job.

Either way it should be easy enough to source an alternative smaller bore m/c so suit a single caliper.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing