Master Cylinder Ratio Chart

[8trackmind]

Ok fellow GS'rs. It's brain pickin time.

Most of us have attempted to make our bikes go faster. Jets, Pods, exhaust...but other than the folks with the GSXR front ends, who has a GS that can hope to stop as well as the newer bikes? That's what I thought.

Anyone used a late model master cylinder?
What size piston in you're master cylinder?
What size pistons are in you're calipers?
Anyone swapped to a two piston calipers like on the 81 is honda CBX?
Anyone found a multi piston caliper that bolts on the stock fork without adapters AND clears the stock wheel?

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

AOD and I have already started some research on this but...decided it may be best to involve the entire GSR think tank.

Sooooo...Do you know what your master cylinder ratio is?

[AOD]

I've had two fairly lengthy chats with Micheal Morse from Vintage Brake and Rob at CycleRecycle2 about improving the braking feel.

First off, Rob said most guys don't properly bleed their brakes, which causes most of the greivance with bad brakes. His suggested key point was to make sure you bleed the master cylinder, as well as the calipers, by cracking the bolt at the banjo to bleed the system. Before going off and trying new pads, master cylinders, etc. - check this.

Rob's thoughts on sizing were a bit backwards from what Micheal at Vintage Brake thought though...

If you refer to the chart on the page 8track posted above, it has some text about brake feel and ratio. Typically how the ratio thing works is the smaller the master cylinder diamter, the higher the pressure / force it can deliver, but it requires more travel.

More lever travel and higher pressure will result in more feel through the brake lever and better perceived braking control.

As you increase the size of the master cylinder diameter, you move the lever less to move the same amount of fluid, however, you have a greater change in fluid flow but less pressure. This results in less responsive, more touchy brakes.

Micheal believes Zook probably went with master cylinders on the larger side, so I need to confirm this before I start speculating exactly what size I should be after. The target ratio for our bikes with two single piston rotors up front (non-opposing) is 14:1.

In the meantime, if anyone KNOWS for sure the diameter of the master cylinders on most GS bikes (state your year/model), please post it. The diameter is stamped into the casting on the bottom of most master cylinders.

~Adam

[Billy Ricks]

Should be right on the master cylinder itself. I may be wrong but I think my stocker was 5/8. I can't confirm that though since I sold it to someone here. The size is usually cast into it near where the banjo fits.

[Macmatic]

Just got done replacing my OE master on the 750EF with one off a Hayabusa. Both were 5/8. This was cast in and confirmed with calipers.

The 'busa master give a MUCH harder lever but I'd say its a 50/50 shot that I never really bled the OE master properly. I "rebuilt" it before putting the bike on the road... reused the old parts but cleaned the gunk out of it and inspected for wear/corrosion. I think the old seals were fine but I may have never "bench bled" it... always had a so so lever.

"Bench Bled" the 'busa and it was hard as a rock after a quick bleed of the upper banjo. I might keep the old master around just to test it out when I get some forks under the project bike...


Oh yeah... simple answer.

1984 GS750EF, 5/8in ID Master Cyl.
2003 Hayabusa Master, also 5/8in

/\/\ac

[8trackmind]

Hmm, I can see now why there aren't many threads on brakes.

[AOD]

Everybody just wants to go fast...not slow down fast.

[Billy Ricks]

Everybody just wants to go fast...not slow down fast.

I don't fit that category. 4 piston pots and PFM ductile iron rotors up front.

[8trackmind]

Everybody just wants to go fast...not slow down fast.

Zactly...:-D

[8trackmind]

I don't fit that category. 4 piston pots and PFM ductile iron rotors up front.

Hey, Billy, I know you have decent brakes. I was thinking of you when I wrote this...:-D
"other than the folks with the GSXR front ends"

[Billy Ricks]

Hey, Billy, I know you have decent brakes. I was thinking of you when I wrote this...:-D
"other than the folks with the GSXR front ends"

Oops.

[8trackmind]

Anybody got a CBX...

with calipers like this?

[AOD]

We all live in reality...not the Barber Museum.

[8trackmind]

We all live in reality...not the Barber Museum.

The caliper...not the bike...
Maintain focus or we will lose all credabilty...8-[

[Mysuzyq]

I got the impression that switching to steel braided brake lines, and the Vesrah kevlar brake pads, along with proper bleeding, gave the GS a significant improvement in braking.....(some here have the ability to stoppie, reportedly:shock: ). I'm inclined towards trying these first, before considering a non-stock master.......in an emergency-braking situation, being able to properly modulate the brakes, and brake hard without lock-up is just as important as outright braking power.....a late model master that can induce a stoppie with two fingers is also a dangerous thing sometimes .

Tony.

[8trackmind]

I got the impression that switching to steel braided brake lines, and the Vesrah kevlar brake pads, along with proper bleeding, gave the GS a significant improvement in braking.....(some here have the ability to stoppie, reportedly:shock: ). I'm inclined towards trying these first, before considering a non-stock master.......in an emergency-braking situation, being able to properly modulate the brakes, and brake hard without lock-up is just as important as outright braking power.....a late model master that can induce a stoppie with two fingers is also a dangerous thing sometimes .

Tony.

Make no mistake, I'm not looking for outright braking power. Nor am I looking for racer replica brakes. I'm looking for what the standard is in 2006.

You have to admit, many of the new Japanese cruisers will out stop a GS. They are just as heavy and many have front wheels that are just as narrow. Even the entry level bikes have a more positive feeling braking system than a GS.

Don't get me wrong, better pads and ss lines are a great start but...There must be more that can be done. You can add all that stuff to a GSXR that already has great brakes and it improves as well.

The master I'm using won't allow a two fingered stoppie. Won't lock the front wheel up either. I have a little too much lever travel and I still have stock calipers. You can, however feel exactly what the brakes are doing.
Which is a nice change.

I'm NOT recomending that everyone change their master cylinder. I do however believe that if we put our heads together, we can come up with a solution that will give our bikes some of the advantages of newer bikes.
The engine is already there, let's do the brakes!:-D

Best regards, Jeff