Topic: CB550 Dual disk brakes

[kevinevo7]

Hi,

I've upgraded my 550 Supersport with original dual disks and calipers, steel brake lines and a master cylinder for 2 calipers.
The system is filled with DOT4 oil and bleeded, the brakes perform OK, but the there is no feel in the brake lever. It's soft and I can almost squeeze the lever completely. I'm pretty sure there is no air in the system.
Is this normal ?

Regards,

Kevin

[flatlander]

i wouldnt' say it's normal. i have a similar setup and after bleeding the lever has a definite "stop".
what diameter master cylinder do you use? what was your process for bleeding?

[robvangulik]

Start simple, try how your setup feels with the original master cilinder.

[kevinevo7]

i wouldnt' say it's normal. i have a similar setup and after bleeding the lever has a definite "stop".
what diameter master cylinder do you use? what was your process for bleeding?

For bleeding I've used a vacuum tool that connects to the bleed nipple and sucks the oil down. After that I've tried the traditional way of bleeding, sqeeuze lever a few times and loosen the bleed nipple ...
The master cylinder is this one http://shop.honda4.nl/catalog/product_info.php?cPath=902_146_214_336&products_id=2666

I think I've got to try the 'reverse' bleeding way

[flatlander]

there is a good post here about bleeding: http://forums.sohc4.net/index.php/topic,259.msg207521.html#msg207521

i do it the "traditional" way of pumping it through the bleed nipple until no bubbles come out then leave the nipple closed. after this there are usually tiny bubbles still in the lines which raise to the top over time. pump a few times (slowly!) with the cap off the master cylinder and you will see them being squeezed out into the reservoir.
you can tape or tie-wrap the lever so it's pulled in towards the handle bar grip, leave the diaphragm off the MC and put the cap on loosely. tap the connection points of the lines a few times with a piece of wood or handle of a screwdriver to loosen bubbles. then just leave it sit over night or so, for the last tiny bubbles to raise into the MC.

takes a lot of words to describe - but it's actually very easy to do.

[kevinevo7]

Thanks, I'll try it out.

[SOHC4 Cafe Racer Fan]

In addition, if you are using a stock master cylinder, I am not surprised with the lack of feel and power to the calipers.  The stock master cylinder was not designed to handle twice the braking.  You should consider upgrading your master cylinder.  If you insist on being period correct, there are numerous options -- including master cylinders from Gold Wing models of the same years.  They were designed to handle larger bore piston calipers and two of them.

[flybox1]

MC's dont care what calipers or pistons or rotors are on the other end of their brake lines.   
MC's only do one thing....push fluid! 
stock MC's can work, but they still only push a certain volume of fluid.  You're asking them to do a little more work.
If you want them to work, you need to do a better job of getting all the bubbles out. 
If you cant, you'll always have that spongy soft braking, because your volume is going compressing bubbles instead of pushing your pistons....and you'll need to upgrade to a MC which pushes more volume.

[SOHC4 Cafe Racer Fan]

MC's dont care what calipers or pistons or rotors are on the other end of their brake lines.   
MC's only do one thing....push fluid! 
stock MC's can work, but they still only push a certain volume of fluid.
If you want them to work, you need to do a better job of getting all the bubbles out. 
If you cant, you'll always have that spongy soft braking, because your volume is going compressing bubbles instead of pushing your pistons....and you'll need to upgrade to a MC which pushes more volume.

I'm picking up what you're putting down.  If the lever feels spongy, it is likely air bubbles.  That said, I don't think that the stock lever moves adequate amounts of brake fluid to 2 calipers.  This would not create so much of a spongy lever but more of a wooden ineffective MC.

[flybox1]

MC's dont care what calipers or pistons or rotors are on the other end of their brake lines.   
MC's only do one thing....push fluid! 
stock MC's can work, but they still only push a certain volume of fluid.
If you want them to work, you need to do a better job of getting all the bubbles out. 
If you cant, you'll always have that spongy soft braking, because your volume is going compressing bubbles instead of pushing your pistons....and you'll need to upgrade to a MC which pushes more volume.

I'm picking up what you're putting down.  If the lever feels spongy, it is likely air bubbles.  That said, I don't think that the stock lever moves adequate amounts of brake fluid to 2 calipers.  This would not create so much of a spongy lever but more of a wooden ineffective MC.

Yes...the finite amount of fluid moved by the MC may or may not be enough to stop the bike from higher speeds (and give the 'feel' the user is needing).  I wouldn't trust old equipment to do more that it was designed to do, especially when it comes to life safety systems 

[flatlander]

he's got one that's designated for double discs - helps if you can read the dutch under his link 
but it doesn't say on that page what diameter it is. i guess it would be something more than 14mm?
mine's 16mm and i'm happy with it.

[robvangulik]

The stock mc, mostly 14 mm is too large for one caliper, that's why everyone is convinced that sohc bikes have bad brakes.
Put a 1/2 inch, 12.7 mil on one caliper and it brakes a lot better. I use a stock 14 mil on double cb400 calipers ( 38 mm a piece) and can make stoppies at will.

[mrfish2]

A master cylinder with a 14mm bore isn't a bad idea for a dual disc set up, the problem is that all of our stock MC's that have a 14mm bore don't push enough fluid for 2 calipers. Hence is why everybody thinks they need one from a Gold Wing or something, but using one from say a GL1000 you run into the problem of the MC pushing the right amount of fluid, but your new bore is close to 17mm (11/16" to be exact) and you are still left with a "wooden" feeling brake lever.

[flybox1]

A master cylinder with a 14mm bore isn't a bad idea for a dual disc set up, the problem is that all of our stock MC's that have a 14mm bore don't push enough fluid for 2 calipers. Hence is why everybody thinks they need one from a Gold Wing or something, but using one from say a GL1000 you run into the problem of the MC pushing the right amount of fluid, but your new bore is close to 17mm (11/16" to be exact) and you are still left with a "wooden" feeling brake lever.

14mm is only part of it.  need to factor in the 'stroke' of the piston as well. 
anything pushing more than stock single disc volume, is sufficient.
a 17mm would be just fine.  if it pushes more volume for the same stroke it will move the pistons plenty and you'll have a nice feel a the lever.
I purchased an <$100 14mm MC for my dual disc setup. 
Its firm at about 1/3 lever travel, and at 1/2 travel my back end gets rather light