What Size Brembo Master Cylinder?

[SEBSPEED]

I may have a deal on a used Brembo master cylinder - if it's the right size...

Stock 86 VFR master cylinder is stamped 5/8", which translates to 15.87 or roughly 16mm.

I am using CBR600F3 calipers on the bike, but they appear to be about the same as the VFR parts(I know, appearances can be deceiving...)

The Brembo unit I can get is 16x18, will this work for me? There might be another available in 19x20, but that seems way out of line with the stock parts?

Thanks!

[V4 Rosso]

Going from RC24 calipers to F3 calipers means reducing the caliper piston area (that is linear to the force applied to the brake pads given a fixed pressure) by a factor of ~1.4 At the same time going from 16 to 19mm implies reducing the area of the master cilinder piston by ~1.4 (linear to brake line pressure given a fixed pivot length and lever force). I do not think the smaller pivot length of the brembo master cilinder makes up for this 80% loss of force that can be applied to the brake pads. What is the pivot length of the RC24 master cilinder?

As slowf2332 mentions, his GSXR caliper pistons have twice the area of the F3's. So a master cilinder that has numbers close to his will not be adequate for your setup. There are more factors that come into the equasion (e.g. rotor & brake pad size), but hydrolic ratio as explained in veefer800canucks post has the biggest impact as demonstrated in the above example.

[Veefer800Canuck]

OK, so to clear all the corn-fusion, I took the liberty of asking Brembo themselves.

I gave them Seb's 4-1-1 and am awaiting their reply.

[SEBSPEED]

Going from RC24 calipers to F3 calipers means reducing the caliper piston area (that is linear to the force applied to the brake pads given a fixed pressure) by a factor of ~1.4 At the same time going from 16 to 19mm implies reducing the area of the master cilinder piston by ~1.4 (linear to brake line pressure given a fixed pivot length and lever force). I do not think the smaller pivot length of the brembo master cilinder makes up for this 80% loss of force that can be applied to the brake pads. What is the pivot length of the RC24 master cilinder?

As slowf2332 mentions, his GSXR caliper pistons have twice the area of the F3's. So a master cilinder that has numbers close to his will not be adequate for your setup. There are more factors that come into the equasion (e.g. rotor & brake pad size), but hydrolic ratio as explained in veefer800canucks post has the biggest impact as demonstrated in the above example.

I was just going to post about the rotor size, funny you mentioned it!

I am using the entire F3 front end - forks, wheel, rotors, calipers, etc.

I just found out that the stock F3 m/cyl size is 1/2".

[SEBSPEED]

OK, so to clear all the corn-fusion, I took the liberty of asking Brembo themselves.

I gave them Seb's 4-1-1 and am awaiting their reply.

Now why didn't I think of that?? :blink:

Thanks Rob! :biggrin:

[V4 Rosso]

I just found out that the stock F3 m/cyl size is 1/2".

As the F3 calipers are similar to the RC36 calipers, and the bore of the m/cyl match I suspect the same goes for pivot length: 1/2"x1"

If that is the case than the 16x18 brembo will be a pretty good match.

[SEBSPEED]

Provided that the radial and conventional style m/cyl's can be swapped apples to apples(16mm -> 16mm).

I'm interested in knowing what Brembo has to say about this.

[Veefer800Canuck]

Provided that the radial and conventional style m/cyl's can be swapped apples to apples(16mm -> 16mm).

I'm interested in knowing what Brembo has to say about this.

Still awaiting their reply.

I did get an auto-response that thanked me for my inquiry and assured me that a LBP (livebreathingperson) would answer me.

[Veefer800Canuck]

I told him I was building up a CBR600F3, and here's what they said:

Hi Robbie,

I was told you had a question regarding Brembo master cylinders. OPP is the Canadian distributor for Brembo motorcycle parts so I can answer any questions you have. Regarding your set-up, you will need to examine your calipers to see which size you should use. If memory serves me correctly, you would have four piston calipers on the front so you could use a 19RCS (which has a 19x18 and 19x20 configuration) or a 19x20 forged master cylinder. If you have an older style of caliper such as a two piston floating caliper, then you would need a 16x18 forged master cylinder.

Thanks!

Nick

[SEBSPEED]

Thanks very much Rob, I love this place!! Now to go find the box with the calipers in it...

[The Phantom]

Another fantastic example of VFRD at work... where else do you find a discussion with such in-depth information that is easy to follow, and with a solution that meets the criteria.

Kudos V4 Rosso, you nailed it!

V4 Rosso: As the F3 calipers are similar to the RC36 calipers, and the bore of the m/cyl match I suspect the same goes for pivot length: 1/2"x1"... If that is the case than the 16x18 brembo will be a pretty good match.

Brembo: If you have an older style of caliper such as a two piston floating caliper, then you would need a 16x18 forged master cylinder.

And Seb you are on the pace, that was the initial solution you proposed.

Slowf2337 and Rob also provided great info, all of which goes to further expand the collective mindset of VFRD. This place is mana for us tinkerers

[JZH]

Er, wasn't it OPP that gave the totally f'd-up explanation in the first place? I've never looked into radial masters, so I have no idea if the same criteria apply as with conventional masters, but it sounds like you guys have sorted everything out--no thanks to OPP! Well done. :laugh:

Ciao,

[KevCarver]

What are you going to use for a brake light?

Dunno yet. You can get pressure switches, right? Either that or find a way to retrofit the Honda microswitch somehow...

My RC51 came with a 19X18 Brembo Radial and standard banjo bolt, but the previous owner suggested I get the pressure switch if I wanted to run it on the street. He included the one he got from the original owner, which was drilled for safety wire and apparently leaked due to the poor job. Anyway, I ordered one from EMA thinking it was a Brembo part and they sent me a Goodridge double banjo pressure switch. It matched the broken one, so I guess thats the one.

It works fine, and turns on with light pressure. It won't turn on as easily as the stock mechanical switch, however it does seem to work without having to mash on it. That's only based on in garage static testing, though. It won't fit the stock connectors on the wire harness, but does come with new ones to attach to your harness wires. Also the appropriate number of washers, three in the case of the double banjo model.

I'm not totally sold on the Brembo Radial yet. Of course that's only with a couple short street rides and no track as yet. It works great, but I can't find the sweet spot of adjustment for my hand. Seems like it is a little too far out, and one click in brings the lever too close to the bar while braking for my comfort. I'm still learning the bike and shaking it down after installing new Vortex clipons, and after my first significant ride I rotated the unit a little forward. That may help, but I haven't been back out. Braking is great, but I haven't tried the stock RC51 master to compare. Maybe the 19X18 isn't the right size for me? Don't know...

I do totally dig the bleeder on the top of the cylinder, though! Swapping the bolt for the new pressure switch bolt was a breeze! About half the air went up into the reservoir tube and I was able to flick the tube until the bubbles went into the reservoir. The rest came out from the bleeder in about two pumps. Bled from the calipers too, just because. Of course, got nothing from them.

For what its worth, my old F3 track bike came with a Suzuki conventional master cylinder with steel lines and stock calipers on EBC Pro Lite rotors. That was a fine setup for the bike. Don't know what size the master cylinder was, though.

[SEBSPEED]

Thanks for the info Kev, I've a 16mm unit on the way, can't wait to try it out! :blush:

The bleeder on top is definitely a plus, I put a bleeder banjo on my F4i when I did the stainless lines, it works well too.

[Veefer800Canuck]

Where did you land with this Seb?

[mello dude]

I may have a deal on a used Brembo master cylinder - if it's the right size...

Stock 86 VFR master cylinder is stamped 5/8", which translates to 15.87 or roughly 16mm.

I am using CBR600F3 calipers on the bike, but they appear to be about the same as the VFR parts(I know, appearances can be deceiving...)

The Brembo unit I can get is 16x18, will this work for me? There might be another available in 19x20, but that seems way out of line with the stock parts?

Thanks!

A bit of an old thread Seb - get it sorted out? If you need help - I can whip the calculator out. - I assume the second number is lever pivot point distance. Just for a comparison, on most honda stocker resourvour type master cylinders the PPD is about 25/26 mm.

I have an RC51 mc on my bike and the PPD is 16mm. (Bore is 11/16" or 17.46mm)

I played the same game when I went for the brake delink on my 5th gen. (In a past life, I was a brake engineer.)

MD

oops sorry canuck - didnt see your post.

[KevCarver]

Actually I was meaning to post to this as well. After two track days on my RC51 with steel lines and the Brembo master, I really dig it! I totally see why some of you guys are all excited about the RC51 front ends on the VFR. The Brembo offers great feel when paired with the steel lines. I don't feel like radial calipers are even necessary. My previous track bike was 636 with radial calipers and standard master with steel lines, and I like my RC set-up better. Before that was F3 with steel lines, EBC Pro Lite rotors, Suzuki standard master, and stock calipers. Good, but least of the three. Naturally.

Oh, and the adjustment knob is super easy to use. Even without the racer style left clipon adjuster cable.

Canuck: I think you could fab up a rear rotor yourself from old beer cans and duct tape with no worries since you have that sweet RC51 front end bolted up!

[SEBSPEED]

Actually, it's funny this came back up! I did get the 16mm master, but have not put it to use.

Yesterday I drove to New Jersey to help a guy install a 929 front end on a 900RR, and in exchange for the work he gave me the complete front end from the 900, the whole thing - triples, brakes with stainless lines, clip ons, and freshly powdercoated wheel with rotors which has a new Metzler M3 on it.

If I can find another 86-89 VFR stem, I am going to put those rotors on an F3 17" wheel and throw the whole shebang on the VFR. Not sure how the 16mm master will play into that scheme, hadn't given it thought yet!

[Veefer800Canuck]

Now there's a development!

MBD combined with ADD. :laugh:

Hey look, a squirrel! :huh:

[SEBSPEED]

Now there's a development!

MBD combined with ADD. :laugh:

Hey look, a squirrel! :huh:

A what?!? Where?!? :blush: :huh:

Rob, if only you could feel the pain I've had trying to find a straight pair of used forks; 2 sets of bent F3 forks so far... I'm really crossing my fingers that the third time's the charm... :blush:

Quick edit - you left out one important acronym... OCD!

[Guest]

This is really a bit easier than you are making it, You need to find the total active area of the pistons, in the calipers. Then figure the ratio of mc area and active piston area. what does this ratio translate to?

at about 20:1 you get very wooden brakes with poor feel

at about 25:1 I'll bet this is pretty close to factory number you get a pretty good street feel and a firm but 2 finger type of brake

at about 27:1 is about the best to me in the feel dept but the lever pressure will feel a tiny bit mushey (1-2 finger brakes at the track)

At about 30:1 you can generally bottom a lever if it does not have a lot of travel

now there is one more factor and that is leverage ratio ie pivot to center of piston shorter = more line pressure less fluid movement and visa versa

why change lever ratio?, well here goes say your setup comes in at 20:1 then you need to reduce the pivot ratio over original, if it comes in at 30:1 you need to go to a longer pivot ratio to return full power to the brakes and pick up a bit better feel.

We used to carry several different bore size m.c. to the track on race day and would go up or down based on the track and conditions.

remember that friction is simply based on rotor contact area and coefficient of the pad material.

for this discussion lets stay out of rotor heat and the like this is all you need for a good base line.

Now the real reason for the radial M.C., It was designed to save space on the handle bars, and nothing more any other "reason" it has an advantage is just hype in the real world, oh yea it is easier to and cheaper to build too, the altered lever ratios can be machined into the same body part and the same lever can be used = less cost for the mfg. by making fewer parts and reducing inventory (this was a secondary bene for the space thing)