Topic: Front Brake Solution Alternatives

[Rosinante]

In 2008, Gordon said this:

Wow! 

Considering I can lock up the front wheel on my K1 with the stock single caliper, I'd have to say yes,  but I still like the way it looks!

I just rebuilt my master cylinder and caliper and installed a fresh hose and pads and while it made an improvement in braking performance, I am quite disappointed and I hope to find a better solution.  Sure, I could install a better, braided SS hose and this would make the system stiffer, less sponginess, but I am looking for a better solution.  Right now, having just completed this rebuild, the front brake basically works no better than the rear drum brake.  It slows the bike down but comes nowhere near Gordon's report of being able to lock up the front wheel.  On my bike, even Arnold Schwartzenegger in his prime could not squeeze this lever hard enough to lock up the front wheel.  Performance is so poor that I consider this front brake dangerous.

I had a '75 CB750K back in the late seventies with FAR better brake performance (at least in my memory).  In my memory the front brake was far more effective than the rear brake.  This is not the case with my current 1978 CB750K.

What are my options?  A master cylinder with a smaller bore would improve braking power, but also increase sponginess.  A braided SS hose would help with the sponginess.  Are smaller-bore MCs available for this bike?

Perhaps I need the dual disk system from a CB750F.  Can these be found?  Where?  This bike, a 1978 CB750K, is very different from the earlier K0-K6 bikes, and even different from the 1977 model.  Would brake parts from an F even work for this bike?

What about grinding the disk to improve friction?  De-glaze.  Would it help?  Would this be only temporary, until the disk becomes smooth and polished again?

How in the world does Gordon get excellent performance out of basically the same stock setup that performs so poorly on my bike?

Thank you, in advance, for reading and considering my questions.

[bryanj]

I think your memory is telling you fibs, not to be rude but do you really think Honda spent so much on R&D and got it wrong? A smaller master bore will need more lever travel to work which means the lever gets close to the bars and fails UK safety inspection for lack of reserve travel.
Fit dual discs with standard master same problem!
Yes the las 750F with twin discs a twin pot calipers stops a bit better, but then that was using the same system as the later DOHC bikes.
Compare it to a newer bike and they are #$%*e BUT  compare a 1078 car to new and you get the same result.
The standard brake with decent(therefore NOT cheap pads) along with all the rest good works fine, my 500 would squeal the front tyre but never lock the wheel, then who wants a wheel locked on a motorbike

[Rosinante]

I think your memory is telling you fibs, not to be rude but do you really think Honda spent so much on R&D and got it wrong? ....

You are not rude at all!

Memory is indeed fallible but consider this:

1)  I am 100% certain that the front brake on my '75 worked WAY better than the rear brake.  I see others reporting the same thing....better front brake performance compared to rear drum brake performance.  This is not the case with my current '78.

2)  Gordon could lock up his front wheel.  Not possible on this '78.  My front brake performance would need to be three or four times better for this. 

Something is just not right.

[Rosinante]

The pads I used are these.  About $23.  Is there a better pad available for my purpose?

______________________________________________________________

Brake Pad (Set/2) - Kevlar - 52 x 20mm. + 52 x 12.8mm.
OEM # 45105-323-023 /45105-323-036 /45105-3223-043A / 45105-390-003 / 45105-390-006A +
45106-323-013 / 45106-323-006B / 45106-390-003 / 45106-390-006B

Fits: Front Disc on Honda CB750K (1977-78),
CB750F (1975-76) Supersport,
CB750A (1976-78) Hondamatic
Part #: 29-3501

[Stev-o]

In 2008, Gordon said this:

Wow! 

Considering I can lock up the front wheel on my K1 with the stock single caliper, I'd have to say yes,  but I still like the way it looks!

On my bike, even Arnold Schwartzenegger in his prime could not squeeze this lever hard enough to lock up the front wheel.  Performance is so poor that I consider this front brake dangerous.

I had a '75 CB750K back in the late seventies with FAR better brake performance (at least in my memory).

First off, I wouldnt want to lock up the front wheel! The CB750 was one of the first bikes in the late 60's to come standard with a front disc brake, it was a simple design, very reliable and adequate stopping power, at least for the 70's. A lot of guys complain that brakes dont work well but are they being compared to modern brake systems? The caliper is a very simple design, not much to upgrade there if you have a new seal?  Thinking the master may be your issue...

[PeWe]

My K6 with dual brakes work really fine. My K2 with single brake does not. Same type of mc, DSS aftermarket mc.
Like my K6 did most of the time before dual.

The old pads with asbestos must have worked better.

[Oddjob]

The biggest difference to brake performance on these type of bikes is the pads. Get reports of some really good ones, consider carbon pads, I haven't tried them yet on the SOHC but they work really well on my CB1300, no dust either.

[pekingduck]

There are inherent faults with the stock single disc Honda brakes. The high stainless content disc compromises appearance for friction, the pivoting 3 piece caliper flexes and doesn't make full contact, and the master cylinder piston is too large.
I think the greatest improvement can be done with a smaller master cylinder, 11 mm or 12 mm piston, so you can modulate the pressure better.  If you could find a cast iron or steel rotor, that would be my next choice.
Brake lines would be my last choice, but tey are cheap to replace.  Stainless braided hoses resist abrasion better, but have the same nylon/teflon inner hose as new OEM rubber hoses, so if you get a huge improvement with them, it was probably from careful bleeding.

[bryanj]

I agree about pads, asbestos was the best but it is now considered too dangerous, does your bike have disc front and back or drum back, we never had K5 or 6 in uk

[Deltarider]

Last winter I have replaced my MC by a repro, which works better than the OEM and I'm not the only one who is of that opinion. Around € 55,- at CMSNL which is just a little more than an OEM rebuild set, which implies a lot of work. I have still the same brake lines bike got in 1976 at the assembly line. At the begin of every season I carefully inspect them. I should add that unless riding, bike is not in direct sunlight. I fear SS lines for me will be a disappointment. That little bit of sponginess I have, is hardly worth mentioning. It has not increased and I like it. I'm in full control and can dose the brake precisely. Back then those brakes were designed to be full proof. You can brake like a fool, and only near standstill you can lock the wheel. I've said it many times before: I estimate the chance you'll be in an accident by panicky braking your super brakes higher than a too long braking distance. Your choice.
After having read unnumerous threads on the subject, where all arguments are repeated over and over again, I can't help the feeling there are quite a few that are above all interested in doing the job.
Yes, there's one bad thing. They suck in rain, but, hey, true gentlemen don't ride in rain.

[MauiK3]

I have dual discs that are drilled, not excessively by tru disc. I have a repro stock master, I could not get my original to stop drooling.
My brakes work much better than single disc did. I have more lever travel but not too much, my smallish hands like it.
I drive conservatively so I’m not doing any big time braking. I’m sure they have plenty of surface area.
I had alignment problems at first but after some adjustment it’s great.

[rotortiller]

Best bang for the buck was a master cylinder with a smaller piston off an EX Kawasaki, more pressure in the line for a better feel, better braking with no wooden lever. Forks do not lend themselves for an easy caliper upgrade. The K7 has a slightly bigger caliper piston which helps a tad. #$%*ty old design it is.

[Rosinante]

Thank you.  This is exactly what I hoped for.  A concise compilation of strategies for better front brake performance.

[pekingduck]

Here's a last comment.  When I was working in Honda dealers in the '70s and '80s, we'd occasionally get complaints that the brakes weren't stopping as well after we changed tires.

And it was true - the greatest stopping power is before the point of skidding/lockup.  Worn out tires that had less traction were easier to make skid, and for new tires with more tread/traction, it just took more effort to get to that point.

[calj737]

Don’t undervalue the critical importance the front suspension plays in braking performance. Have you rebuilt the front forks? Are the springs rated for your weight? The fluid? Did you set any preload?

A stiffer suspension (versus mushy, spongy suspension) will transfer better traction to the tire, increasing the stopping power. By all means, get your brake components and lines on top shape, but do not overlook the forks.

[Rosinante]

Duly noted, and I have been meaning to focus on the forks.  But seriously, these front brakes barely slow the bike down.  There is no taxing pressure on the tires or the forks.  Just pathetic braking.  It takes me 30-40 feet to stop from 20 mph.

[calj737]

It takes me 30-40 feet to stop from 20 mph.

Then you have a component problem. Either the hoses are leaking (check the brake light switch area) or the master cylinder is shot.

[Oddjob]

Pads could be glazed. Try different pads and bed them in properly. Clean the rotor of all the old pad transfer with brake cleaner, go out and do 10 stops from 30mph with very light brake pressure, don't allow the bike to stop, get to 5mph and then go back to 30mph, allow the disc to cool, after those 10 do 10 stops from 45mph with moderate brake pressure, again don't stop. Lastly, stop and check the disc and there should be pad transfer on the surface of the disc. like a light grey film. Do 10 stops at 60mph with full braking pressure. Pads should now be run in.

[MauiK3]

Sometimes the pucks get hung up in the caliper, be sure to check that they move freely.

[gmet]

Duly noted, and I have been meaning to focus on the forks.  But seriously, these front brakes barely slow the bike down.  There is no taxing pressure on the tires or the forks.  Just pathetic braking.  It takes me 30-40 feet to stop from 20 mph.

I,ve been dealing with the exact same issue. I had cb 500s, 750s,350s all that had better stopping power in the front then my 72 750 does. I rebuilt the caliper, tried two oem M/C's and purchased a nice cast rotor out of australia as well as new ss hoses and the stopping is pathetic, barley locks on grass. So I then tried a Honda CBR600F4 M/C which someone recommended with no change. I've tried oem pucks and now using EBC orange painted organic sintered pads? Same awful braking. The change to a 12 or 13mm M/C keeps coming up so I guess I'll go that route. I've done the bedding procedure, bled the lines, got a great firm lever but dont want to ride it due to lack of braking. I've checked for proper alignment on the caliper holder etc...
I've never had so much trouble getting a set of front brakes sorted out. I've been running bikes for 40 years and this one is stumping me. 
Any ideas would be a big help.

Oh, any idea what the bore size is on a Kawaski EX M/C? is that a 500?

[rotortiller]

13mm (Nissin 1/2"). There are other 13mm masters available that do not move enough fluid due to a smaller piston stroke and unsuitable lever geometry. The problem was they pulled too close to the handlebars.

[Rosinante]

Update:  Braking has gotten a little better, perhaps due to bedding.  Still underwhelming.

I think I still have the pads that were on this bike when it came to me about 10 years ago and there is still meat left.  Might be worth popping them in there to see what happens.  Somebody mentioned the evil asbestos OEM.  I suspect one thing that could fix this is a very soft, sticky pad.  One that would wear out more quickly but stop better.  If such a puck exists.  Pads is a potential solution.

MC with smaller bore is also a potential solution and if it results in a spongier feel then that would be because of the increased hydraulic pressure, which is a good thing unless you run out of level travel.  SS brake line would likely be the thing to install along with that smaller bore MC.

Dual disks might also be a solution but one I would prefer to avoid.  Just more unsprung weight, which is a bad thing, and should be unnecessary.  Perhaps someone will still chime in here with a story of how their brakes became twice as effective.  I'd settle for twice, but 3 times would be better.  Some folks have suggested it is best to have brakes that the operator basically cannot lock up, and I don't agree with that.  I'd like brakes that good but also, this bike would have to have WAY WAY WAY more braking power for that. 

I'm feeling the same way as gmet.  Brakes this poor give me an uneasy feeling. 

Here is the spec for this bike:

30 - 0 mph :  10m
60 - 0 mph :  41m

I notice several things about this.  First, this is actually not much poorer, or maybe near the same as, my current braking performance.  Pathetic.

I have a car, same 1978 model year, that can brake at least this good and weighs five times as much.  No ABS.  Yes, front tires can be locked up even with modern tires, but this is safer than not being able to brake at edge of adhesion.  What we call "threshold braking."  I feel safe in this car.  I feel unsafe on this motorcycle.

Another thing I notice is that today's tires are LIGHT YEARS ahead of stock 1978 tires.  I cannot overstress this.  If these stock braking specs were at the edge of 1978 tire adhesion, then that 60-0 MPH distance could be cut by a third!

Discuss.

[Rosinante]

I appreciate that rotortiller, and I think the right brake hose might address this.  If you think about it, the MC and caliper are not flexing and fluids are inelastic (cannot be compressed).  So ALL of that sponginess is in the hose.

[pekingduck]

Since you rebuilt the master cylinder, you might have the old piston to measure the diameter.  I think it would be 14mm or 12.7mm (1/2").

[calj737]

Sintered pads offer the best friction. Comparing the braking performance of a 4-wheeled vehicle to a motorcycle is irrelevant. The weight of the vehicle helps promote friction when the brakes are applied despite the mass energy involved in stopping distance.

A single piston caliper on a nearly 50 year old motorcycle will feel like crap when compared to your memory and to modern equivalents. Even with more modern compound tires. If you want to avoid dual disc setups, then upgrade your single piston caliper to a 2 pot caliper and fabricate a mounting package and adapter for the rotor. There’s ample examples from others doing this. You can retain a stock appearance and benefit from improved braking.

Me, I’d upgrade to two modern calipers and modern rotors if you plan any measure of spirited riding. But that’s me.