soft brakes twin disc set up

I agree with both of the points that are made by Patton and luc above. I trust engineers and I have roadraced moderns bikes. My R6 could lock the front wheel from over 120mph with just one finger and I never locked the wheel unintentionally.

I would advise the original poster to install some good brake lines, which are a good upgrade on an old bike ,and see what the results are.

The braking " power" is the result of 4 things:
1/ the COF (The coefficient of friction) between the disc and pad
2/ The size of the contact area between the pad and the disc
3/ The clamping force applied to the disc.
4/ The diameter of the rotor

#1 can be adjusted by using pads with different COF
#3 can be adjusted by changing the MC bore size.
#4 use the same principle than a torque wrench

If you read the many reviews of the Z1 during the 70',you will notice that quite a few testers complained about the lever requiring way to much force and even a few suggesting that the bike needed a smaller M/C bore ( or 2 discs with the same MC)

My comment, from someone that had been using it for the past 10 years, was simply to point out that stating that using a 14mm MC on a dual disced Z1 make the system over sensitive and can result in locking up the front tire in an emergency stop, is not correct when you compare it to newer bikes.
What is over sensitive: a bike where you can lock the wheel at 120mph using a single finger or one where you need a lot of effort and ALL your fingers to do so?

luc wrote:

The braking " power" is the result of 4 things:
1/ the COF (The coefficient of friction) between the disc and pad
2/ The size of the contact area between the pad and the disc
3/ The clamping force applied to the disc.
4/ The diameter of the rotor

#1 can be adjusted by using pads with different COF
#3 can be adjusted by changing the MC bore size.
#4 use the same principle than a torque wrench

If you read the many reviews of the Z1 during the 70',you will notice that quite a few testers complained about the lever requiring way to much force and even a few suggesting that the bike needed a smaller M/C bore ( or 2 discs with the same MC)

My comment, from someone that had been using it for the past 10 years, was simply to point out that stating that using a 14mm MC on a dual disced Z1 make the system over sensitive and can result in locking up the front tire in an emergency stop, is not correct when you compare it to newer bikes.
What is over sensitive: a bike where you can lock the wheel at 120mph using a single finger or one where you need a lot of effort and ALL your fingers to do so?

ditto

I guess Im just not proficient enough,but the first lever I reach for in a hard stop is the clutch--so I can shift down and use engine compression for a quick slow-down or stop.Locking up the rear tire with its larger contact patch seems a lot safer than locking up a front tire and losing all steering control.I seldom use my front brake and that only for holding the bike at a traffic lite.I been riding that way for a long-g-g time and no issues yet.I guess if bikes were FWD and being pulled instead of pushed I would feel differently.bj

The problem with locking up the rear wheel is all the weight is being shifted forward as you stop ,taking weight off off rear wheel and sticking it over the front wheel.

Thats the reason for those big rotors on the front and small ones on the rear ,just like on a car/truck.

dam10r wrote:

I have a 1977 kz1000. I recently switched out from a single disc to a double disc set up. I think I got all of the correct parts from a motorcycle salvage. But I can't get the brakes to work right! There is no bite. I still have the original master cylinder which I know can affect feel. But I thought I would still have some braking. Am I just not bleeding them right??

Amazing how fast things can go off on a tangent (or several) !!

No bite:


Are the pads new ? You may have gotten some oil contaminated pads from a salvage bike with bad fork seals.

Soft lever feel:

Even properly bled you will now have a softer lever feel due to using your existing 14mm M/C. Install some good brake lines and the soft feel will disappear.

IMO (ducking !) New pads and new lines combined with your existing M/C should give you a pretty good braking system, one with adequate feel, control, and power.

mjg15 wrote:

dam10r wrote:

I have a 1977 kz1000. I recently switched out from a single disc to a double disc set up. I think I got all of the correct parts from a motorcycle salvage. But I can't get the brakes to work right! There is no bite. I still have the original master cylinder which I know can affect feel. But I thought I would still have some braking. Am I just not bleeding them right??

Amazing how fast things can go off on a tangent (or several) !!

No bite:

Are the pads new ? You may have gotten some oil contaminated pads from a salvage bike with bad fork seals.

Soft lever feel:

Even properly bled you will now have a softer lever feel due to using your existing 14mm M/C. Install some good brake lines and the soft feel will disappear.

IMO (ducking !) New pads and new lines combined with your existing M/C should give you a pretty good braking system, one with adequate feel, control, and power.

good point,if the pads are glazed over they wont grab.
if the lever feels solid with no air in it id try scuffing up the pads and rotors to knock glaze off of them

Was fortunate enough to own and enjoy riding several brand new Z1's, and enjoyed reading a plethora of Z1 magazine articles and reviews, but didn't share the complaining testers' concerns, as Z1 front brake would readily squall the tire on clean dry pavement without undue lever squeezing effort.

Kawasaki's factory right hand double disc conversion kit (Part Number 99990-523) was offered as an optional extra for the Z1. Among other components, the kit included a larger 5/8" bore master cylinder to replace the smaller 1/2" or 14mm single disc size m/c.

The similar optional factory kit for 1977 KZ1000-A1 also included a larger 5/8" bore master cylinder to replace the smaller 1/2" or 14mm single disc size m/c.

Presumably, there were legitimate engineering reasons for the the larger m/c, but I don't know the particulars.

The oem barrel shape m/c reservoir used on large Kaw fours through 1977 (single front disc) was changed to a trapezoidal shape reservoir on 1978 KZ1000-A2 with 14mm m/c (same single front disc). The trapezoidal shape reservoir in later years was used with a 5/8" m/c (dual front discs).

As far as I know, Kawasaki never produced a dual front disc brake model with the smaller 14mm master cylinder.

Meanwhile, have never desired to lock the front wheel while riding, regardless of speed.
But sometimes had it squalling on the verge of locking. And wasn't particularly concerned with the number of fingers required (probably because of the adrenalin).

The vast improvements in modern brakes are imo not necessarily aimed at reducing strength of hand grip required at the lever. But toward such things as less fade, less heat retention, etc. Brakes are getting so good and so sensitive (and perhaps so toggle-switch), that ABS may soon be par for the course.

Also enjoyed some rather extensive touring on a 1984 Gold Wing Aspencade 1200 with oem dual front discs and inter-connected brake system. As I recall, the front brake lever operated only the front brake, but the brake pedal operated both front and rear brakes (perhaps the rear disc plus just one front disc?). And it wasn't possible to apply only the rear brake.

Just guessing, but perhaps the horror stories are in part due to onset of a severe emergency braking situation before the rider grew accustomed to the more sensitive front braking.

Meanwhile, be careful with the front braking on those damp curvy mountain roads with patches of wet leaves, sand and loose gravel. Locking the front wheel is bad enough when the bike's perfectly upright. It's really bad when leaned over.

Good Fortune!

"Just guessing, but perhaps the horror stories are in part due to onset of a severe emergency braking situation before the rider grew accustomed to the more sensitive front braking."

That will make perfect sense.

PLUMMEN wrote:

The problem with locking up the rear wheel is all the weight is being shifted forward as you stop ,taking weight off off rear wheel and sticking it over the front wheel.

Thats the reason for those big rotors on the front and small ones on the rear ,just like on a car/truck.

I can dig it ,especially on a FWD car. Ive never had a bike swap ends with the rear brake firmly applied. However,I have had dirty skivvies a time or two when I instinctively grabbed a handfull of front brake in a near miss situation.Then the bike wanted to swap ends and my end was clutching vinyl.Oh well,to each his own driving style.Be safe all.bj

hocbj23 wrote:

I guess Im just not proficient enough,but the first lever I reach for in a hard stop is the clutch--so I can shift down and use engine compression for a quick slow-down or stop.Locking up the rear tire with its larger contact patch seems a lot safer than locking up a front tire and losing all steering control.I seldom use my front brake and that only for holding the bike at a traffic lite.I been riding that way for a long-g-g time and no issues yet.I guess if bikes were FWD and being pulled instead of pushed I would feel differently.bj

And you are still alive to post here? Amazing!!

Dude, use your front brake and stay alive!!
Seriously.

The only time I use the rear brake on my 750 twin is when I'm already at a stop and use it to keep the bike from rolling.

I don't know if I could lock the front tire with just one finger, but I know I could with two.

Mix and match brake components:

96 GPz1100 master cylinder (15mm I think)
Dual braided stainless lines between master cylinder and calipers. Got rid of that brake splitter.

83 GPz750 calipers.

80 KZ1000 brake disks

on a 79 KZ750 twin.

I love it!! Best brakes I've ever had on a bike! I can easily out stop the 85 GPz750 Turbo and the 82 KZ1000.

GPz750 has 10" brake rotors, the 1980 KZ1000 has 12" brake rotors. That's 20% more radius which equals 20% more stopping power using the same calipers.
I think the GPz750 had a 5/8" master cylinder but I'm not sure. If true then that would account for even more stopping power with the 15mm.

Been two years so far and no problems yet.

I think I could do a stoppie, but I lack the intestinal fortitude to attempt it. :blush: