Rebuild Master Cylindet VS Upgrade ??

jammer415

Been Around the Block
1972 CB450

My front brake needs an overhaul... Getting SS lines and rebuilding the caliper with a SS piston.


Master cylinder options:

Option 1) Rebuild the stock master cylinder (Genuine Honda rebuild kit is $49).

Option 2) Buy entirely new universal-fit master cylinder from eBay ($35-$50)

Option 3) Retrofit a genuine Honda master cylinder from a newer model (which model??)


Any thoughts?
 
So I’m thinking that retrofitting from a more recent model is the ideal option out since once I determine the correct bore size, I should be able to find a good used one on eBay... I’m thinking Nissin or Tokico are most reliable brands to look for?

Stock master cylinder for CB450 is 13mm or 14mm? Ideal replacement size?

Can I bump it up to 15mm for more bite? Or is that too much for a single piston CB450 caliper?
 
I get the front master/brake lever for the CRF's for most of my builds. You can get them for $30 on eBay.

https://www.ebay.com/itm/HONDA-FRONT-BRAKE-MASTER-CYLINDER-FOR-CR125R-250R-CRF250R-450R-CRF250X-450X-/122758730929?_trksid=p2385738.m4383.l4275.c10
 
I ended up putting a nissin master from a cbr600 on my cb360. Works amazing. Just slightly more leverage. Not too much. Also ran a braided line directly to my caliper. The cbr master has a built in bleeder and brake switch too so I was able to ditch the stock switch, and bleeding from the top is amazing.


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redrover said:
Stock master cylinder for CB450 is 13mm or 14mm? Ideal replacement size?

Can I bump it up to 15mm for more bite? Or is that too much for a single piston CB450 caliper?

I have a 450 sitting here, but unfortunately, there does not seem to be any designation of the bore size (unless there is some Honda code - there are some markings). Regardless, if you want more brake for less lever pressure, you need to go to a smaller bore size, not larger. There is a mechanical limit, so the ratio of diameters between the MC bore and caliper bore (actually this is the ratio of piston areas) has to be somewhat close to the original design. This is because the way that the caliper releases from biting the disc is only the elasticity of the caliper piston seals. The displacement of the MC has to be great enough to displace more than the fluid displaced in the caliper when the seals retract the piston(s). Generally, even a tiny reduction in MC piston diameter makes a BIG obvious change in lever pressure. The trade off is a "springier" or "spongier" lever feel, though often this is less pronounced than the improvement in power.
 
irk miller said:
I get the front master/brake lever for the CRF's for most of my builds. You can get them for $30 on eBay.

https://www.ebay.com/itm/HONDA-FRONT-BRAKE-MASTER-CYLINDER-FOR-CR125R-250R-CRF250R-450R-CRF250X-450X-/122758730929?_trksid=p2385738.m4383.l4275.c10

These look awesome! And you can’t beat the price.
 
thrillseeker said:
I ended up putting a nissin master from a cbr600 on my cb360. Works amazing. Just slightly more leverage. Not too much. Also ran a braided line directly to my caliper. The cbr master has a built in bleeder and brake switch too so I was able to ditch the stock switch, and bleeding from the top is amazing.


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Wow nice... Which year cbr600 did you use??
 
jpmobius said:
I have a 450 sitting here, but unfortunately, there does not seem to be any designation of the bore size (unless there is some Honda code - there are some markings). Regardless, if you want more brake for less lever pressure, you need to go to a smaller bore size, not larger. There is a mechanical limit, so the ratio of diameters between the MC bore and caliper bore (actually this is the ratio of piston areas) has to be somewhat close to the original design. This is because the way that the caliper releases from biting the disc is only the elasticity of the caliper piston seals. The displacement of the MC has to be great enough to displace more than the fluid displaced in the caliper when the seals retract the piston(s). Generally, even a tiny reduction in MC piston diameter makes a BIG obvious change in lever pressure. The trade off is a "springier" or "spongier" lever feel, though often this is less pronounced than the improvement in power.

Hmm ok so you’re saying the brakes will feel more spongy, but if you squeeze harder it will actually utilize more power to be able to brake harder?
 
redrover said:
Wow nice... Which year cbr600 did you use??
2007. It's in my build thread here http://www.dotheton.com/forum/index.php?topic=44726.msg703240#msg703240


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thrillseeker said:
2007. It's in my build thread here http://www.dotheton.com/forum/index.php?topic=44726.msg703240#msg703240


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Wow awesome build, just read through literally the entire thing haha. Super cool. A lot of good info.
 
redrover said:
Wow awesome build, just read through literally the entire thing haha. Super cool. A lot of good info.
Thanks! Hopefully you can learn from all my mistakes. Ha


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redrover said:
Hmm ok so you’re saying the brakes will feel more spongy, but if you squeeze harder it will actually utilize more power to be able to brake harder?

Right. You are trading lever travel for power. You have to move the MC piston further for the same amount of caliper piston(s) travel. Obviously, there is a limit where the two components must be within a certain range of each other - i.e. you can't get so much advantage with a smaller piston MC that you physically can't move the lever far enough. Personally I have never had his happen though - possibly due to luck - I have never bothered to calculate the end result as it has always seemed easier to simply bolt up the parts. As these have always been on hand, I never had to make an investment in a new, untried combo that didn't work. Regardless, I invariably use small diameter high quality braided steel lines which expand very minimally under pressure so I've never had much of a "spongy" feel - just a little more lever travel. By the way, calipers' retract their pistons by the seals returning to their normal shape, so the required volume of fluid displaced is fixed regardless of what is happening at the MC, so if you did happen to use a MC that simply did not produce enough displacement, the brake would simply not work with a single squeeze of the lever.
 
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