honda CBs - smaller bore master cylinder

jackseattle

jackseattle

New Member
Anyone able to coax some better braking power out of the stock single piston caliper by switching to a smaller bore m/c? I'm not that keen on the resulting braking power after I switched out the old rubber lines for braided stainless lines and installed some new vesrah race compound brake pads. The table over at vntagebrakes.com got me thinking that a smaller bore master cylinder (10-12mm) would create noticeably more braking power than the stock 14 mm bore m/c. How'd it turn out and what other mods did you have to make? I have the stock throttle assembly and front brake light sensor still on the bike.
 
Race Compounds usually give ppor performance cold....Usually need to be hot to work....

EBC brake p[ads are Organic...Kevlar based. Once broken in, they seem to have better than stock braking power. I am running Ss lines, stock MC.

The EBC were about the same when I first put them on, but 100 miles into them they have really improved. I can squeal the front wheel and not lock it up. I like the progressive control. The brakes were never this goods stock. For reference, I bought the Bike form the original owner in August 1978, with only the 1978 riding season on it. The brakes were "new" and while marginally better then drums, not so hot.

With the Ss lines and new EBC pads, I would call them adequate now, which actually is a nice improvement.
 
I'm using an 11mm master cyl.
It puts enough pressure to flex caliper bit feels 'spongy'
More pressure doesn't mean much better braking with stock pads.
I like EBC but prefer HH grade (doesn't seem to be available any longer though :( )
 
I went and ordered what is supposed to be 10 mm bore size master cylinder and can let you know how it works. Wouldn't be surprised if the bore ends up being larger than that.
 
Won't a smaller piston m/c give you a weaker pull because it is pushing less fluid. I know that happens if you use a single disc m/c on a dual disc set up?
 
I thought it would, in theory, have more power, but lever throw should increase when using smaller m/c. Now that I'm thinking about this, would a smaller m/c also reduce the caliper piston travel?
 
It feels 'spongy' even though you can see the caliper distorting so your putting higher pressure on it
 
OJ said:
I thought it would, in theory, have more power, but lever throw should increase when using smaller m/c. Now that I'm thinking about this, would a smaller m/c also reduce the caliper piston travel?
Click to expand...

Smaller piston means you are moving less fluid so it tales more travel of the lever to move the pistons the same distance as a bigger piston moving more fluid. If it feels spongy it is either air in the lne compressing giving you less pressure on the pistons or rubber lines expanding doing the same thing.
 
Try reading that again, the caliper distorts because the pressure is MUCH higher, nothing to do with air in the system or lines balooning
 
Just saying, spongy feeling is normally from what I described. I'm having a hard time understanding how it could be putting so much force to flex the caliper and still be spongy. It could be spongy for the reasons I said and once the air is compressed will have enough pressure to flex the caliper. I would first bleed the system again to make sure there is no air left in it and if that doesn't eliminate the spongy feel replace the line with braided steel. If that doesn't work I would replace the caliper. Something sounds fishy with the whole problem right now.
 
the flexing of the caliper is what is making it spongy.

The ratio of the caliper piston area to the MC piston area multiplies the force. The smaller the MC piston, the more force you can put on the caliper. The ration determines the travel too. Smaller MC piston, less travel of the Caliper piston for a given movement of the lever.

The smaller piston on the MC increases the leverage of your hand pressure. Enough that the caliper is getting enough force to bend the mount.
 
Read mydlyfkrysys explanation, that's the reason
I've been doing this stuff a while and know how to bleed brakes, even with S/S lines ::)
It isn't distorting the mount though, the bolts can't keep the pads parallel
 
Project completed. I found a Nissin 11mm m/c from a 1999 Suzuki SV650, hooked it up to my s/s brake lines, bled the lines, and then let it sit overnight with the brake lever pulled in about 50%. MUCH better braking power. I get positive braking force when I start to pull the brake lever, and the caliper really bites the rotor now. Letting it sit overnight with the brake lever pulled in allowed the air bubbles to exit the brake lines through the return hole in the m/c reservoir. thanks everyone
 
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