SOHC.co.uk Forums > CB750
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:
--- Quote from: Lobo on April 19, 2020, 11:36:14 PM ---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!
--- End quote ---
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:
--- Quote from: Lobo on April 21, 2020, 11:42:05 PM ---... 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!
--- End quote ---
Will do as soon as we get out of this bloody lockdown.
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