Topic: Dual Disc Conversion questions-Master Cylinder

[Bikebuff]

Good Morning All!

I'm collecting parts for the dual disc conversion on my 1970 cb750 K0 and I have one question about the master cylinder.  I've read that a modern master cylinder from a dual disc sportbike is a good way to go.  So, here's the question: would a master cylinder from a larger sportbike (ie: Honda CBR 929/Fireblade 1000) be a better idea since it is capable of slowing a larger and higher horsepower bike, or would a master cylinder from a CBR 600 be adequate enough? I don't want to take chances with an underperforming master cylinder. 

Thanks!

Prost!

[ProTeal55]

I believe any master with a 5/8 bore will work 4 ya..
An easy way to pick the correct one is to just look to see if the bike the master was originally installed on had dual disc brakes from the factory. I bought a new Nissin 5/8 bore master for my CB750 project becasue I didnt want to deal with a used one (had bad experiences with one, didnt want to go down the road again)...

The master I got for the CB450 project WILL NOT work for a dual disc application becasue the Diaphram is too small to support two calipers/discs (but it looks pretty slick )

[eldar]

Most anything for a dual disk app will work. I would not want to drop below a 500 bike though.

[Geeto67]

It takes more pressure to operate a single caliper setup than it does a dual disc setup. Probably because with dual disc the "normal" stopping forces are much less per caliper. On most single caliper systems the M/C has a smaller piston which leads to higher line pressure than a dual disc system.

For kicks (and mostly because the MC went bad) I replaced the master on my 78F cafe bike (dual disk) with one from a 76f (single disc). I find that the new master does a better job overall of stopping the bike than the one on my 6000mi stock 78F, however the stock 78F has more lever "feel", meaning it is a little easier (less lever travel) to lock up the brakes on my cafe F than on my stock F (my stock 78F has more brake control through the lever).

My next expirement is going to be using a MC from an 82 450 sc nighthawk on the dual disc brakes and see how it will work (more concerned with the diaphram than with the piston size).

If you really want a sport bike m/c then I think only the suzuki's have a werid banjo bolt size (I have to remember what it is), other than that the cbr's should work (and I know a bunch of DOHC cb750 guys who use them).

[Bikebuff]

Great!  I think I'd like to stick with a Honda m/c, and I'll probably try and get one from a cbr 600 or 1000.  Thanks much for the input.  Any thoughts on how to correctly measure the amount of stainless braided line I need and any recommendations on who I should go with (Galfer, HEL, etc.)?

Prost!

[Geeto67]

Great!  I think I'd like to stick with a Honda m/c, and I'll probably try and get one from a cbr 600 or 1000.  Thanks much for the input.  Any thoughts on how to correctly measure the amount of stainless braided line I need and any recommendations on who I should go with (Galfer, HEL, etc.)?

Prost!

just did braided line on my buddy's goose (that's Guzzi to the non italians) and here is how we did it.

Proped the bike on the main stand and then ratcheted the back of the bike to the work bench so that the front end was off the ground and full extended. Since he didn;t have existing lines I taped the fitting to one end and then ran the line the way I wanted to go to the other end (where the fitting was installed on the caliper). I then gave myself an extra inch of "screw up room" and began to install the fitting at one end. Once I got it without screwing up I would cut 1/2" off the other end (if I screwed up I would just cut the 1/2 inch and start over) and install that fitting (the logic being that slack is always better than it being close to tight). I suppose you can install one side and then measure but we did it that way because we had a long coil of braided line and it was easier to work with in segements. We used fittings and line from Earls and it all went together fairly easy.

[eldar]

Really all braided lines seem good. I have yet to see anyone complain about a braided line of any make.

[gerhed]

I have run both off the stock master cylinder.
But you have to pump it a couple times to get 'em both to clamp.
This is O.K. as long as you're not in a big hurry to stop right Now!

[chippyfive50]

Great!  I think I'd like to stick with a Honda m/c, and I'll probably try and get one from a cbr 600 or 1000.  Thanks much for the input.  Any thoughts on how to correctly measure the amount of stainless braided line I need and any recommendations on who I should go with (Galfer, HEL, etc.)?
Prost!

I just asked the braided line question  in another thread, and the consensus seemed to be that the HEL,and Galfers were fine but that the Speiglers were the nicest, but they are $20 more...I haven't ordered any yet..
I can't say enough about the NISSIN M/C...it is really nice. $129.00
 http://shopping.speedwerks.com/catalog/c0m0bm0b0s1pn0p4182np0

[Shadowjack1020]

Here's a site I learned about from Randakk's site (one of my other bikes):

http://www.vintagebrake.com/mastercylinder.htm

I believe he sells the 5/8" Nissin M/C as an upgrade for early Goldwings. More details on his site at http://www.randakks.com/

Terry

[Geeto67]

Here's a site I learned about from Randakk's site (one of my other bikes):

http://www.vintagebrake.com/mastercylinder.htm

I believe he sells the 5/8" Nissin M/C as an upgrade for early Goldwings. More details on his site at http://www.randakks.com/

Terry

well that is a heck of a lot easier than my trial and error method.

[Bikebuff]

Thanks for information everyone.  I checked out both websites and was wondering about the Nissin website (Shindy's).  When ordering, it asks if you want 5/8" or 14mm piston.  ChippyFive, which did you pick?  Does it matter?

Also, ChippyFive, I love the paint scheme on the bike in your avatar.  Is the light green a factory color?


Prost!

[dpen]

I got a master from an early Honda Rollerdoor & it works brilliantly with the twin disc

[batdan]

Here's a site I learned about from Randakk's site (one of my other bikes):

http://www.vintagebrake.com/mastercylinder.htm

I believe he sells the 5/8" Nissin M/C as an upgrade for early Goldwings. More details on his site at http://www.randakks.com/

Terry

Looking at that website it seems to suggest that the single 38mm single piston caliper on my cb750 oughto have a master cylinder size of 10-11 mm! I'm pretty sure it comes with a 14mm master cylinder so that seems ridiculous.
It seems like a larger master cylinder feels more solid while a smaller one will feel more "squishy" but will actually give more line pressure and thus more braking power. And also it should be more controllable because since it's squishy you'll be able to control pad pressure more linearly. But of course if you brake too hard then you can lock the front wheel which is always a disaster.  Is 14mm really the ideal for a bike with stainless steel lines and modern tires? Perhaps going down to 12 or 13mm for a master cylinder would give more braking power without causing a huge chance for accidental lockups?

This site http://www.yoyodyneti.com/category.aspx?categoryID=2733 seems to sell all sorts of different size brembo master cylinders. Perhaps I'll buy a smaller size as an experiment  because I destroyed my stock master cylinder and need a replacement anyway. If it doesn't work well I can just sell it and buy a different size.

[Shadowjack1020]

I don't know all that much about this, but according to Randakk, the master cylinders on first-gen disk brakes were entirely too large, because of the perceived idea that they shouldn't be TOO powerful. Which is why my '77 Goldwing has an 11/16" front master. As time drew on, the feel and power expected changed and the size of the bores went down.

[paulages]

i haven't got around to changing the stocker out on my 550, and it brakes quite well with dual disks. it has a strange feel---kinda soft like car brakes, but still quite efficient. if you have to pump several times, you have air in the lines, not too small a m/c.