Are front drum brakes really that bad?

Hiya,
I'm pretty confident that I need to do most of a front end swap on my KZ400 S2 with drum brakes in front. The forks are bent and the wheel rim is rusted through in sections.

My kneejerk reaction was to replace the front end with a disc brake setup because I'm under the impression that's better than the drum brake currently installed. I don't actually have a good reason for thinking discs are better though so wanted to see what folks here think since there are likely a few front drum brake users floating around.

It also sounds like there are issues finding seals for the KZ400 stock brake calipers. To avoid that I was considering doing a front end swap from a KZ440, wheel, forks, brakes and all. Those seem to mostly be the cast type wheels rather than spokes so I'd eventually have to seek a matching rear and I'd be moving away from stock which I'm on the fence about.

Does anyone have any ideas on whether going out of my way to ensure a disc setup is necessary or if drum brakes are really as bad as they're made out to be? The only one I've ever used was the rear brake on my first bike, a Honda Shadow 125. It was fine but that was just normal, low duty, rear brake use so doesn't really help.
If the bike gets back on the road I'm not going to be taking it to any race tracks or anything. Normal road use, no drag races

My impression is that the biggest issue with drum brakes is that they can have mechanical positive feedback.  That is, the drag of the shoe against the drum can pull the shoe into the drum, increasing the braking effect automatically, which pulls the shoe in more, which increases the braking force, which pulls the shoe in more.... until the wheel locks up.

I think the better drum brakes were configured in a way that tries to reduce this effect.  The twin-leading-shoe drum.  I don't have any idea how common that was.   www.motorcyclespecs.co.za/Techinicale/Le...shoe_drum_brake.html

Also, drum brakes are not great a self-adjusting which requires regular checking and maintenance.  Hydraulic disk brakes are very good at self-adjusting.

And I think disk brakes are better at shedding heat, since the disk is exposed instead of enclosed inside the hub.  And since the job of all brakes is to turn kinetic energy into heat, that seems like a good benefit.

If it were me, I'd convert a front drum brake to disk if I were actually going to ride it.
 

Drums in good working condition will stop your 400 just fine. 
Drums  have a weakness in older  bikes of the shoes delaminating from the backing and causing wheel to lock up. ( rare , but happens )
Drums in motor cycle applications are cable or mechanically  activated
Discs are lighter  , Always hydraulic giving more options in locating  controls, Easier to modulate pressure for better feedback. 
Disc are self cleaning  and  shed heat better. .
Dave

I don't actually have a good reason for thinking discs are better

Every motorcycle manufacturer on the planet has a good reason or they never would have changed, Disc brakes are simply superior....

Every motorcycle manufacturer on the planet has a good reason or they never would have changed, Disc brakes are simply superior....

I understand and I should have been clearer in my question. It's not that I don't believe what I've read but I didn't have a good understanding of why disc brakes are better. Now that I'm at a point where I can choose my replacement I need information to base my choices on.
There's an added clause to the question that goes 'are the easily replaceable disc options for the KZ400 that much superior to the drum alternatives that I should discount drums entirely when planning a swap'.
I don't really have the know how to put the twin 300mm brakes from my old FZS600 on this bike but if I did that's what I'd be considering. Without that ability I'm left with more 'straight swap' options like the KZ400 disc which probably doesn't perform quite as well as the Fazer's did.
 

Drums in good working condition will stop your 400 just fine.

This and the other information helps a lot, based on all the information here I'm going to seek out a disc based swap but it's good to know that I can swap out the shoe and eliminate some issues if I'm forced into a drum replacement.

Sounds like the summary of what makes drums a poorer choice goes:

• Potential delaminating of old shoes
• More potential to lock wheel due to positive feedback (braking action can pull the system into a more engaged state)
• Greater mechanical complexity and frequent maintenance needs
• More potential to overheat due to the enclosed braking system
• Greater weight
• Don't look great do they (my own opinion
  
  )

Thanks for all the information, this really helps a lot and I'm convinced to limit my search to disc based swaps.

wrote:

Don't look great do they (my own opinion

)

 

I don't know. Some of them look pretty cool.  I still don't want one, but the vents and fins and external linkages look neat.


 

wrote:

I don't know. Some of them look pretty cool.  I still don't want one, but the vents and fins and external linkages look neat.

Haha - fair enough I do see what you mean. I do find the one on the 400 a little... boring? It's so personal I'm not even sure why I think that because it's not like I see them often.
I think if there weren't quite so many cons to drums I'd have considered keeping them just because they're different. I can see the look growing on me over time if not for that.

You have had a lot of good information returned, but I will add a few more thoughts on this.  Brake fade to repeated use, feel and wet.  Disc brakes have far better resistance to brake fade then drum brakes especially with repeated use in a short time span.  Part of this is due to the fact exposed rotors cool off much faster than drums do, so in repeated hard braking events disc brakes work much better.  The large drum brake "air scoops" in the attached pictures were an attempt at increased drum cooling, but they never were as effective as good disc brake setups.  Disc brakes also offer a much better braking "feel" to the rider than drum brakes ever could.  This leads to better and more efficient brake application by the operator once he/she understands what threshold braking is all about.  Drum brakes also had an uncanny way of feeling different as they would heat up and cool down.  Disc brakes also tend to work much better in wet conditions than drums do especially if water or moisture gets inside the drum.  There aren't many things as interesting in life as trying to stop a motorcycle with wet drum brakes.  Don't ask how I know this....
My vote always favors disc brakes.

Rick H.   

P.S. Watch a night time Nascar race and pay attention to the disc brake rotors on the cars in the race.  It is absolutely amazing to watch how fast the brake rotors heat up red hot and cool off within just a few seconds.  Drum brakes could never take this sort of usage.

A properly set up front drum brake should still be enough to get you into trouble if you grab a handful at the wrong time.

I recall reading about a service some company was offering where they would make the drum and the shoes concentric so the shoe would make 100% contact with the drum. i think once the shoes begin to wear that will more or less occur naturally but can't say for sure.

I'm working on a KZ440B project right now. I intentionally chose the B because I wanted the retro look, including the spokes and the drum brakes. The front will eventually be vented as shown in the pics DOHC posted. The plan is to start relacing the wheels this weekend so we'll see how that goes.

wrote:

There aren't many things as interesting in life as trying to stop a motorcycle with wet drum brakes.  Don't ask how I know this....


 

Gotcha - that level of variability is a little frightening. I'm more than ok with as much consistency as I can get in my brakes.
Side note, I've never watched Nascar, is it any good beyond the example of brake resilience? Expensive to watch? Not sure if it's subscription etc.

wrote:

I'm working on a KZ440B project right now. I intentionally chose the B because I wanted the retro look, including the spokes and the drum brakes.

That sounds like a fun project. I love the spokes look on these bikes particularly, the whole thing goes together super well. Hoping to see how this weekend goes for you! 
 

Oh there is no doubt a drum brake can get you into trouble when you least need it.  Going back to my younger days in factory fast cars with drum brakes, you had one or two hard applications of the brakes and then they would start to fade, or give out as we used to say.  There were a few things you could do to make things a bit better such as very aggressive linings and such.  In my days as a mechanic at a dealership we had a special "arching" machine to grind material off the brake linings until they made complete contact with the drums.  At that point the linings were "married" to the drums and you better not mix them up or else.  It was an art using that machine properly.  In those days we only trusted riveted brake linings, not glued ones.  Guys would machine slots or holes into their backing plates and drums trying to get more cool air into their brakes, but it also allowed more moisture in too.  Disc brakes came on the scene and all those issues went away.

To your question about NASCAR, there is no simple response.  NASCAR today is not the NASCAR of the past.  It used to be racing of and for the masses pitting manufacturers against one another.  It was fun to watch and root for your favorite driver, manufacturer and team.  Drivers came in all sorts of types and personalities and if you couldn't find one that you liked you weren't looking hard enough.  Unfortunately, NASCAR became almost too popular and race directors started to "sanitize" the sport.  Certainly it was made safer especially after Dale Earnhardt Sr. was killed, but rules came into effect that made cars and powertrains almost identical.  At that point I lost almost complete interest in the sport.  When it became difficult to tell one make car from another and NASCAR started cultivating drivers I gave it up.  The individuality of the sport was lost to me and NASCAR became nothing more than a scheme to make money for the owners and directors.  I just used the NASCAR night time racing example as it shows the continuous use of disc brakes in the extreme and the abuse they can take while still working effectively.

Rick H. 

Just to add my 2 cents, the way a brake works is by converting "kinetic" energy into heat. The biggest advantage of a disc brake as others have said is dissipating the heat (a cold drum works just as well for a equal friction serface)
The phenomenon described by DOHC of a drum pulling itself on is called the "self servo effect" and is an intential part of the design.