Topic: cb400F front brake upgrade?

[Bailgang]

For those of you who check out the pissed off thread, you're probably well aware of my first ride on my 75 cb400F ending abruptly when I encountered a lawn tractor crossing my path. With hindsight being 20/20 I beat myself up wondering if I had only done this or that to avoid it but I can't change the past and I'm done beating myself up over it. However I am certain that if the front brake had just a bit more braking power, I would've had that precious 1/2 second needed to clear that tractor. The front pads were new, I can't remember the brand but they are semi sintered and hadn't had enough miles on them to be bedded in. That's kind of the irony because I was planning on bedding them in during the ride but met the tractor mower before I got around to it so I'm willing to give the pads the benefit of the doubt at least for now. My question what can I do with its existing brakes to improve its ability to stop? It currently has...
Rebuilt factory MC
New OEM style (not SS) brake hoses
Semi sintered pads
Drilled rotor
Rebuilt caliper with new SS piston

I've read other threads on this topic and someone mentioned replacing the factory 14mm MC with a 12mm MC. Can someone give me a lesson in hydraulics 101 on why the 12mm MC would give better braking power than the factory 14mm MC? I'm a long way off before I can put a serious effort into repairing the bike but in the meantime I'm gathering info so I know what parts to look for.

[Bailgang]

Here's a pic of the inboard pad, I'm not a brake expert but it seems like it was no where near bedded in and lucky if 50% or less of the friction material was making contact. Yipes.

[grcamna2]

Scott,the SS OEM rotors on our bikes are more slippery than cast iron which is a much superior(+ coefficient of friction)brake rotor material;I recommend a cast iron replacement rotor;I don't know who sells them yet.
The OEM Honda 1/2" (12.70mm) is a much better choice than the 14mm stock master cyl.

The CBR600F2 has this size for their OEM dual discs and that master has an adjustable lever also.

[Quattrocilindri]

For those of you who check out the pissed off thread, you're probably well aware of my first ride on my 75 cb400F ending abruptly when I encountered a lawn tractor crossing my path. With hindsight being 20/20 I beat myself up wondering if I had only done this or that to avoid it but I can't change the past and I'm done beating myself up over it. However I am certain that if the front brake had just a bit more braking power, I would've had that precious 1/2 second needed to clear that tractor. The front pads were new, I can't remember the brand but they are semi sintered and hadn't had enough miles on them to be bedded in. That's kind of the irony because I was planning on bedding them in during the ride but met the tractor mower before I got around to it so I'm willing to give the pads the benefit of the doubt at least for now. My question what can I do with its existing brakes to improve its ability to stop? It currently has...
Rebuilt factory MC
New OEM style (not SS) brake hoses
Semi sintered pads
Drilled rotor
Rebuilt caliper with new SS piston

I've read other threads on this topic and someone mentioned replacing the factory 14mm MC with a 12mm MC. Can someone give me a lesson in hydraulics 101 on why the 12mm MC would give better braking power than the factory 14mm MC? I'm a long way off before I can put a serious effort into repairing the bike but in the meantime I'm gathering info so I know what parts to look for.

Well, here is the hydraulics explanation:
https://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html

[slikwilli420]

I'm going to disagree on the stainless being no good. I run a single stock drilled disc on my race bike and with a good caliper it is very adequate. The key is good caliper. Stock is total garbage. A 2 piston caliper from AP or grimeca is a great period choice and more than enough for your needs on the street.

[Bailgang]

Well, here is the hydraulics explanation:
https://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html

I had to read that a couple times and let it soak in but I think I understand. Thanks for the link.

I have an MC from a cbr600 f4i but it turns out to be around a 15mm bore, it wouldn't work for my application anyhow because aside from the bore size, it has no where to put the mirror and neither does an OEM cbr600 F2 MC. There are plenty MC's to choose from, I just have to keep looking.

I'm not a metallurgist but I think there is some truth about SS being "slicker" than cast iron but the factory SS rotor should suffice. One thing for sure is that the new pads were no where near being bedded in yet. I have an 83 goldwing which has linked front brakes, the front MC only actuates the left front caliper while the right front caliper is linked to the rear MC and it's left front caliper was lame at best. I was all set to un-link the front brakes but under the suggestion of a member here (can't remember who) I put in a set of EBC HH pads on the left caliper and it went from lame to being able to do a stoppie. Problem is I don't think EBC makes a pad for the 400 using that same friction material as the HH pads on the GL.

[grcamna2]

The member here 'godffery' can have a person cut your stock SS disc with a certain swirl pattern(I had that before,it was on a flywheel resurfacing machine)that will cause it to bite more aggressively with stock type organic pads.I'm surprised that you haven't seen a set of pads somewhere online to install to the disc as it is now,which are 'sintered metal' pads which bite very hard.

[Bailgang]

I'm surprised that you haven't seen a set of pads somewhere online to install to the disc as it is now,which are 'sintered metal' pads which bite very hard.

I surprise a lot of people Ive had luck before with semi sintered which is why I chose them on this bike but I'll have to look into full sintered as an option as well.

[scottly]

Regarding the hydraulics, it may be easier to absorb if you look at it from the ratio of MC piston area to caliper piston area. In a nutshell, the larger the ratio, the easier the lever feel for the same amount of braking force. With a stock 14mm MC and 38mm caliper, this works out to 7.4:1. With a 1/2" MC, it would be 9:1, and with a 12mm, 10:1. I'm currently running a 10.4:1 ratio with a stock 14mm MC and a single two piston caliper and a 320mm rotor on my 750, and it works well for me.
I seem to recall something about someone swapping a CM 400 fork onto a CB400, which allowed better brakes?

[Scott S]

 How did you mount the two piston caliper? Any pics or details on this anywhere?
I'm going to disagree on the stainless being no good. I run a single stock drilled disc on my race bike and with a good caliper it is very adequate. The key is good caliper. Stock is total garbage. A 2 piston caliper from AP or grimeca is a great period choice and more than enough for your needs on the street.

[newday777]

 How did you mount the two piston caliper? Any pics or details on this anywhere?
I'm going to disagree on the stainless being no good. I run a single stock drilled disc on my race bike and with a good caliper it is very adequate. The key is good caliper. Stock is total garbage. A 2 piston caliper from AP or grimeca is a great period choice and more than enough for your needs on the street.

I've been wondering about that caliper too. I tried to Google it but didn't find anything on them. Links are always helpful.....

[Bailgang]

Regarding the hydraulics, it may be easier to absorb if you look at it from the ratio of MC piston area to caliper piston area. In a nutshell, the larger the ratio, the easier the lever feel for the same amount of braking force. With a stock 14mm MC and 38mm caliper, this works out to 7.4:1. With a 1/2" MC, it would be 9:1, and with a 12mm, 10:1. I'm currently running a 10.4:1 ratio with a stock 14mm MC and a single two piston caliper and a 320mm rotor on my 750, and it works well for me.
I seem to recall something about someone swapping a CM 400 fork onto a CB400, which allowed better brakes?

While searching for info I ran across a thread about the cm400 forks on a cb400. As far as the hydraulic lesson, I had assumed the bigger the bore of the MC meant more pressure which would mean more clamping force but after reading the link along with your explanation, the amount of pressure the MC can put out isn't determined by the bore of the MC but rather how hard my hand can squeeze the brake lever. Using the same hand on both a 12mm and 14mm MC, the 14mm may feel firmer than the 12mm but that's only because the 14mm is trying to push more volume of brake fluid on that squeeze compared to the 12mm but not more pressure. To put it in a nutshell, it's about leverage. Do I have it figured out right?

[slikwilli420]

 How did you mount the two piston caliper? Any pics or details on this anywhere?
I'm going to disagree on the stainless being no good. I run a single stock drilled disc on my race bike and with a good caliper it is very adequate. The key is good caliper. Stock is total garbage. A 2 piston caliper from AP or grimeca is a great period choice and more than enough for your needs on the street.

I've been wondering about that caliper too. I tried to Google it but didn't find anything on them. Links are always helpful.....

This is what I use on my race bikes. Been the top choice for decades in period racing.

https://andover-norton.co.uk/en/shop-details/18254

I have never mounted one to stock forks but have seen a few different mounting brackets that allow you to adopt this style to stock forks. I run GL1000 forks so the mounting is much easier. This caliper will make a world of difference coupled with the proper master cylinder and good SS lines.

[calj737]

For those of you who check out the pissed off thread, you're probably well aware of my first ride on my 75 cb400F ending abruptly when I encountered a lawn tractor crossing my path. With hindsight being 20/20 I beat myself up wondering if I had only done this or that to avoid it but I can't change the past and I'm done beating myself up over it. However I am certain that if the front brake had just a bit more braking power, I would've had that precious 1/2 second needed to clear that tractor. The front pads were new, I can't remember the brand but they are semi sintered and hadn't had enough miles on them to be bedded in. That's kind of the irony because I was planning on bedding them in during the ride but met the tractor mower before I got around to it so I'm willing to give the pads the benefit of the doubt at least for now. My question what can I do with its existing brakes to improve its ability to stop? It currently has...
Rebuilt factory MC
New OEM style (not SS) brake hoses
Semi sintered pads
Drilled rotor
Rebuilt caliper with new SS piston

It goes without saying, the only thing that matters is you survived and will recover.

To your point about what changes to your bike you might make to improve your chances next time, I’d offer the following advice: consider your tires also. From the pictures, you had a set of Shinkos that are a decent bias ply tire, but in no way are they as effective as more modern radials. Yes, I know it’s hard to source radials in the stock equivalent sizes, but they are out there.

Braking (relying heavily upon the front only) unsteadies a bike. It transfers all weight forward, compresses the suspension, and requires the front tire to perform all the road friction force to slow you down. At a minimum, using both sets of brakes is necessary and possibly would have provided you that extra moment of steering around. That is unknowable but is typically supported by post-incident analysis.

Regardless, front brakes alone are not the answer. Front, rear, tires, riding/braking techniques are what keep you safest and performing best (racing). Braking wins races, braking saves lives. It is a skill all too frequently left unpracticed despite our years of riding experience. Nothing within here is meant as a sleight or criticism, only intended to offer you more information to consider as you rebuild the bike and ride again.

As always, very happy to hear you’re recovering and my empathy for your accident. Good on you for wearing the proper gear too!

[Tim2005]

The CM400 front end is mine.  Precisely it is a CM400 front wheel (18" reverse comstar) with early CB400N forks, discs and calipers and CB400NC yokes. Matching rear reverse comstar off something too It gives you lots better brakes, a very light wheel and you can fit tubeless tyres too. Finding the parts is tricky nowadays.

On a different 400 I've improved the stock brake to adequate, using drilled disc, EBC semi sintered pads (AP Racing ones are aok too, softer though) and a braided hose. I'd like to try another master cylinder next though have yet to spot one with the right bore, hose fitment point , and mirror mounting thread.

[Bailgang]

Nothing within here is meant as a sleight or criticism, only intended to offer you more information to consider as you rebuild the bike and ride again.

As always, very happy to hear you’re recovering and my empathy for your accident. Good on you for wearing the proper gear too!

Constructive criticism is a good thing, thanks for the tips. Riding a bike I wasn't familiar with yet didn't help but what really bit me was that I was totally unprepared when it unfolded. When approaching an intersection I always try to plan ahead as to what will I do if that car over there pulls out and so on, I basically prepare myself so I can react if needed. This mower incident caught me totally surprised and off guard because her pulling in front of me with her mower like she did was the very last thing I expected. That surprise without a doubt delayed my ability to react and when I did, I became fixated and couldn't take my eyes off the mower and being the bike goes where you are looking lead me straight to her.

I'm now hyper-aware of mowers and it's a good thing too. Yesterday a neighbor a block away was mowing with a push mower, as I was driving by she too didn't look and walked right out into the road, she did it again later on my way back with her rider mower, and both times she was embarrassed and apologized. Good thing for her I had been keeping my eye on her as I approached with my truck and was ready to react.

[scottly]

If you had better brakes, you might have been able to avoid the collision, or at least lessened the impact. The 12mm MC is probably the easiest upgrade for a 400; since the forks only have mounts on one leg, you can't do a double disc like on the 550 and 750. In order to mount a better caliper, you need to change the fork legs to ones that have the mounting lugs on the back of the legs, like the 750 F2/F3 and GL, which is why I mentioned the CM400. Tim, would the CB400 wheel have worked with the CM front end? Are the fork tubes the same diameter as the CB; if so, they should slide up into the CB triples.
The AP and Grimeca calipers have two opposing pistons, and have no hydraulic "leverage" advantage over a single piston of the same size since they cancel each other out; the only reason to use them is to comply with "vintage racing" rules.
The two piston Honda calipers I referred to have both pistons on the same side, which doubles the piston area, so a 32mm caliper has as much area as a single 45+mm piston. There may be a factory bracket that would allow the two piston caliper to bolt up the CM fork leg, just like on the F2/F3 and GL.
I swapped the forks on my Seeley to the late F parts just so I could use the two piston calipers: I had noticed that my '82 FT 500 Ascot had an excellent front brake, with a rotor the same size as a stock 750, a 14mm MC, and a single 30mm two piston caliper, which is just shy of the area of a F0/F1 K7/K8 42.8mm caliper. I did some testing and found the two piston caliper performed much better than a K7 caliper, then adapted a 320mm Ducati rotor with a 32mm caliper and HH compound pads. The end result is braking on a par with or better than a dual disc setup, and less weight than the stock 750 single disc setup.
     

[grcamna2]

If you had better brakes, you might have been able to avoid the collision, or at least lessened the impact. The 12mm MC is probably the easiest upgrade for a 400; since the forks only have mounts on one leg, you can't do a double disc like on the 550 and 750. In order to mount a better caliper, you need to change the fork legs to ones that have the mounting lugs on the back of the legs, like the 750 F2/F3 and GL, which is why I mentioned the CM400. Tim, would the CB400 wheel have worked with the CM front end? Are the fork tubes the same diameter as the CB; if so, they should slide up into the CB triples.
The AP and Grimeca calipers have two opposing pistons, and have no hydraulic "leverage" advantage over a single piston of the same size since they cancel each other out; the only reason to use them is to comply with "vintage racing" rules.
The two piston Honda calipers I referred to have both pistons on the same side, which doubles the piston area, so a 32mm caliper has as much area as a single 45+mm piston. There may be a factory bracket that would allow the two piston caliper to bolt up the CM fork leg, just like on the F2/F3 and GL.
I swapped the forks on my Seeley to the late F parts just so I could use the two piston calipers: I had noticed that my '82 FT 500 Ascot had an excellent front brake, with a rotor the same size as a stock 750, a 14mm MC, and a single 30mm two piston caliper, which is just shy of the area of a F0/F1 K7/K8 42.8mm caliper. I did some testing and found the two piston caliper performed much better than a K7 caliper, then adapted a 320mm Ducati rotor with a 32mm caliper and HH compound pads. The end result is braking on a par with or better than a dual disc setup, and less weight than the stock 750 single disc setup.
   

scottly,which model Honda did you use as a donor for that 32mm dual piston caliper;also is that a custom caliper mount bracket you have in the picture with the 320mm rotor front wheel ?
More questions  What are those black fork lowers in the pic? and which wheel is that ?

The CM400 has 33mm fork tubes,same as the CB400F.

[scottly]

The lowers are F2/F3 750, the 32mm calipers were fitted to V65 Hondas, as well as others, the wheel is a Morris, which is a direct replacement for the stock spoke wheel, and yes, that is a custom bracket to use the caliper with a 320mm rotor instead of a 275mm rotor. There is more info on this thread:
http://forums.sohc4.net/index.php/topic,89771.125.html

[grcamna2]

The lowers are F2/F3 750, the 32mm calipers were fitted to V65 Hondas, as well as others, the wheel is a Morris, which is a direct replacement for the stock spoke wheel, and yes, that is a custom bracket to use the caliper with a 320mm rotor instead of a 275mm rotor. There is more info on this thread:
http://forums.sohc4.net/index.php/topic,89771.125.html

That's a very solid looking front brake system

Which bike uses a 275mm rotor that has a mount for that twin pot caliper:the V65 ?

[dave500]

any smaller bore master will give you more clamping effect on the pads for the same effort but more lever travel,which also gives more feel not like the wooden rock hard normal feel,i run a 12 mm cheapie on a cast iron disc.
i got the disc here in australia on ebay a guy makes em solid or drilled,was only bout 150 bucks,you gotta drill out the factory rivets and bolt it on,imagine after all these years if the stock one was cast,they would all be gone from rust?i could paint the un contacted areas but i like the look,this brake does NOT fade and gets better once hot,before this i had 3 or 4 good hard corners and no brake!the stainless was used for looks?i live in a hilly area and dont need to pass any stop lights etc from home all day,my brakes gets taxed!

[Bailgang]

Excellent information guys. I had read before about MC piston dia and it never made sense until now, it's amazing the things you learn when you ask questions.
For now the plan is to use a 12mm MC and go from there, I like the dual piston caliper idea as well but I might save that idea for my 77 F2.