Twin disc caliper modification?

[philward]

Great job - and the thread will be great for future converters

[sprinta]

Thanks for the replies and comments.

With respect to the use of a GL1000 master cylinder. Having only just recently had my original master cylinder re-anodised I would wish to continue using it but clearly if it proved not provide the necessary braking force then I would look to replace it with a GL1000 or similar version.

As indicated, there would appear to be two lengths of the Z900 brake hose, one is the same length as the Honda one and one is slightly longer, see attached. Fortunately the one I had was the longer  one. However, the std Honda one may be OK? It depends on how you intend to secure the hose. As I wanted to use the original hose brk I needed a slightly longer hose another type of retention may allow the std Honda hose to be used?

With respect to the GL1000 disc bolts. I think you will find that they are no longer available new, see attached.  I bought mine s/h from DK or Two Wheeled Spares on e-bay, see attached,together with the caliper and caliper brks etc. They currently still have a number of sets available. I was fortunate with the the bolts and plate I bought as the bolts were as new and the plate reusable, so you need to look at the photos carefull or ask them to give a condition status before purchase.

[K2-K6]

Nice looking job Sprinta.

... I’ll be interested to learn if the braking is 2x improved. My K2 stops like a pig (even with sintered pads) ... it takes a lot of effort at the lever. If the (original?) master cylinder pressure output is effectively halved as now supplying 2 brakes, are you actually better off? This is doing my head in!

As you indicate,  it's hard to follow the theory through without seeing the inversions taking place. 

From running a contemporary system with twin disc and standard mastercylinder years ago on a 750 K2,  I can vouch for it being twice as powerful.  They really are potent in that arrangement and come close to the feel of a modern system in their ability to bring the tire to its limits of grip. That's accomplished with longer lever travel though. 

The larger reservoir used on some is simply to cope with any additional displacement of fluid during pad wear,  and avoid running it into aerating the line in extreme situation.

The leverage is dependent on the mastercylinder bore obviously,  but if you add another piston / caliper it changes the ratio insofar as the same effort at the lever now exerts something like twice the clamping force on both calipers. 

The original system was much more limited by the chosen ratio rather than any particular torque shortfall of both disc and caliper. They are quite a significant diameter on the 750 after all.

[Lobo]

... thanks K2-K6. You’ve forced me to think further, and what I see now is the same pressure being applied .... but over twice the area. (Ie the pressure is not halved; but rather the pad area - defacto braking force - doubled.)

Sprinta... be sure to keep us posted!

[sprinta]

... thanks K2-K6. You’ve forced me to think further, and what I see now is the same pressure being applied .... but over twice the area. (Ie the pressure is not halved; but rather the pad area - defacto braking force - doubled.)

Sprinta... be sure to keep us posted!

Will do as soon as we get out of this bloody lockdown.

[Bryanj]

Correct with pressure but you have to move twice the volume so lever comes farther back. When i twin disced a 500 back in the 70's Girling had just started doing Honda bits so bought a GL1000 one from them

[71 V12]

Thanks for the replies and comments.

With respect to the use of a GL1000 master cylinder. Having only just recently had my original master cylinder re-anodised I would wish to continue using it but clearly if it proved not provide the necessary braking force then I would look to replace it with a GL1000 or similar version.

As indicated, there would appear to be two lengths of the Z900 brake hose, one is the same length as the Honda one and one is slightly longer, see attached. Fortunately the one I had was the longer  one. However, the std Honda one may be OK? It depends on how you intend to secure the hose. As I wanted to use the original hose brk I needed a slightly longer hose another type of retention may allow the std Honda hose to be used?

With respect to the GL1000 disc bolts. I think you will find that they are no longer available new, see attached.  I bought mine s/h from DK or Two Wheeled Spares on e-bay, see attached,together with the caliper and caliper brks etc. They currently still have a number of sets available. I was fortunate with the the bolts and plate I bought as the bolts were as new and the plate reusable, so you need to look at the photos carefull or ask them to give a condition status before purchase.

Hi Andy, I ordered the GL1000 bolts from DK which I received today, and as with you in as new condition 👍👍👍

Do you have a Kawasaki part number or application for the longer brake hose?

Many thanks,

Kevin

[sprinta]

Thanks for the replies and comments.

With respect to the use of a GL1000 master cylinder. Having only just recently had my original master cylinder re-anodised I would wish to continue using it but clearly if it proved not provide the necessary braking force then I would look to replace it with a GL1000 or similar version.

As indicated, there would appear to be two lengths of the Z900 brake hose, one is the same length as the Honda one and one is slightly longer, see attached. Fortunately the one I had was the longer  one. However, the std Honda one may be OK? It depends on how you intend to secure the hose. As I wanted to use the original hose brk I needed a slightly longer hose another type of retention may allow the std Honda hose to be used?

With respect to the GL1000 disc bolts. I think you will find that they are no longer available new, see attached.  I bought mine s/h from DK or Two Wheeled Spares on e-bay, see attached,together with the caliper and caliper brks etc. They currently still have a number of sets available. I was fortunate with the the bolts and plate I bought as the bolts were as new and the plate reusable, so you need to look at the photos carefull or ask them to give a condition status before purchase.

Hi Andy, I ordered the GL1000 bolts from DK which I received today, and as with you in as new condition 👍👍👍

Do you have a Kawasaki part number or application for the longer brake hose?

Many thanks,

Kevin

Hi Kevin

Good that you also managed to get a good set of bolts from DK.

With respect to the longer Kawasaki hose. As indicated there appears to be two possible lengths available. The longer one is around 380mm compared to the shorter one which is around 360mm, which looks to the same length as the std Honda ones?

The Kawasaki code No is: 43059-011 however, I can't advise if that is the longer or shorter version you would need to ask whoever you purchase it from it's length before purchase.

I would also hold back until you decide how you are going to anchor the hose as you may well find that the std Honda one may suffice?

Andy

[71 V12]

Hi Andy,

Did you get a chance to ride since the twin disc upgrade?

Interested to know your impression of the brake performance.

Regards,

Kevin

[sprinta]

Hi Kevin

I have been a bit amiss by not following up with impression of the twin disc conversion.

I've done around 200 miles on it over the last couple of weeks or so.

The extra weight certainly took me by suprise on the first ride with the extra weight dropping the front into corners quiet noticeably, but I soon got used to it and it now give a sense that the front end is firmly planted to the road.

Yes, the twin disc does make a considerable diffierence and certainly worth it, in my opinion.

As the pads I used were a bit thick I had to reduce their faces and I also bevelled the edge's, perhaps a bit too much as only about 40% of the pads are currently in contact with the disc but even so it is a significant improvement and will clearly improve as more of the pads wear into contact with the disc.

No, they are not in the same league as modern brakes but they are certainly as good as twin disc bikes of the same period such as the Suzuki GT750 and the Kawasaki Z900A4, both of which I own so can comfortably make the comparison.

The std master cylinder works just fine and I can see no reason to go for anything larger, such as the GL 1000 etc.

One thing I have noticed is that the speedo cable runs very close to the outer edge of the disc and after the first run it had cut into the outer plastic covering of the cable. I have overcome this to a degree by packing the cable to the mudguard stay and time will tell as to if this is a satisfactory solution?

So overall I am very happy with the conversion which I have found to improve the the braking, as long as you accept the limitaions of any twin disc setup of that period.

The only down side, as previously expressed, is that it will be necessary to have to remove the whole caliper and brk assy to get the front wheel out, which will hopefully only ever be needed to change the tyre.

Andy

[robvangulik]

Drilling the discs can make a considerable difference in weight! I removed 1,5 kg in total from 2 discs.

[71 V12]

Hi Andy,

Many thanks for the update, it sounds like the effort and cost is well worthwhile.

I need a day or so to complete the job on my K4, your information has been very helpful and great motivation👍👍

Regards,

[sprinta]

Drilling the discs can make a considerable difference in weight! I removed 1,5 kg in total from 2 discs.

Totally agree that losing some weight would help and I'm sure that braking would be further improved with thiner discs as they would heat up much quicker.

But as I want to keep the bike as std as possiible neither are options or routes I can go down, such is the price of originality, even with twin discs.

[Bryanj]

Kunifer never corrodes and is a damn sight easier to form to shap, also gives a beter flare in my experience

[sprinta]

Kunifer never corrodes and is a damn sight easier to form to shap, also gives a beter flare in my experience

That is why I used it to make the RH solid brake line. However, it does have a slightly coppery finish so I had a length zinc plated before bending and flaring it to match the original finish of the LH side.

I see that all new replacement solid brake lines have an olive finish.