Topic: What size mastercyl. is necessary for 550 dual-disk conversion?

[A Grove]

Just got my dual-disk pretty much done... I need a new MC with a bigger bore to push the fluids to both calipers.  What "size" or bore dia. would be good for a stock dual-disk conversion? running two stock calipers, that is.  Also, where are you all sourcing your hydraulic fittings/hose to fit to this set-up?

Thanks a ton

[FunJimmy]

Even with two stock (single piston) calipers the fluid demands aren't that high compared to modern dual (multi piston) brake setups.
Using a master cylinder with a smaller piston will increase the mechanical advantage on the calipers at the expense of lever travel.
Modulation and feel will also be enhanced with the smaller piston master cylinder. Alternatively, a master cylinder with a larger piston will feel firmer at the lever and require a firmer pull to achieve the same stopping power of the smaller master cylinder.

If you find a master cylinder from a modern single caliper bike like a Buell Blast you will probably have a good compromise and a mirror mount too.

Good luck
FJ

[rachet]

Thanks FJ, Good stuff to know!

Rach-

[A Grove]

Oh wow, FJ. From my experience with bicycle disk brakes, etc. I was positive it was just the opposite. I thought you had to use a larger-than-stock mastercylinder because you are needing to push twice the fluid.  I was under the impression if it was pushing less fluid you would have less power and thus not gaining tons with the dual-disk?


Not doubting you, just confirming I supposed.

[FunJimmy]

Here's a great explanation of the prinaples used in all hydraulic systems.

http://science.howstuffworks.com/hydraulic1.htm

Cheers
FJ

[ev0lve]

Nice explanation. I had thought it was a 1 to 1 relationship with the upside of the larger MC piston being more fluid for a shorter throw but not necessarily that it would require more force at the lever.

It's fun learning things. 

[coyotecowboy]

Well said Jimmy!!

I was afraid I was gonna have to explain all that stuff again, lol.

Go here while you're at it >>> http://www.vintagebrake.com/mastercylinder.htm

This guy really knows his #$%*

[bryanj]

If you want it to look the same you need an early goldwing master cylinder which has the brake light switch on it then you can remove the hydraulic brakelight switch on the 3 way adaptor and just bolt up the extra flexible with a standard banjo bolt.

Having done tis you do need a bigger bore master to push more fluid to move both pistons

[A Grove]

Thanks for all the information, all.  I think im going to upgrade to a different M/C for sure... probly try to find one similar to what FJ suggested.

[WHALEMAN]

I have dual's on my 1972 CB750 and I used the stock master cylinder. I used stainless braided line from the master cylinder to each disk. The key is using speedbleeders that allows ALL air to be purged. I have a good hard lever with maybe just a little more pull than stock. About the same as single disks that have not been perfectly bled of all the air. Dan

[A Grove]

Dan - I've done a decent amount of bleeding over the past few years... With these brakes the only way I found fit to bleed was from the top ---> down.  Open bleedport, squeeze lever, close bleedport. repeat.  This has worked fine for me.. I have use syringes in the past but didnt feel it was necessary here.  What system/how are you bleeding your brakes?

Also... does anyone feel that any noticeable difference will be achieved by running a similar-bore, but MODERN M/C?  Due to leverage ratios, etc...  thanks

EDIT: I got lots of information, but still cannot find the caliper dia and m/c dia of the stock 550k brakes.  Anyone? or should I just start tearing into them to measure myself.

[bryanj]

From memory so dont quote me

Caliper piston diameter 37 or 38 mm
SOHC master cyl diameter 14mm
GL1000 master cyl Diameter 17mm

[A Grove]

Awesome, thanks bryan.  That helps me a lot.