| Author | Message | ||
     Puddlepirate |
Anybody know what size the XB master cylinder bore size is? It should be stamped on the side of the reservoir somewhere. I'd appreciate the info! Puddlepirate | ||
| Gentleman_jon |
Assuming that you are talking about the front brake master cylinder, it is 1/2". It is stamped on the underside of the cylinder. If you are contemplating replacing this master cylinder, you will find that most front brake master cylinders are larger, 5/8", if I recall correctly, as most sport bikes have twin discs. It is unwise to use a anything larger than 14mm as a front master brake cylinder as the required force at the brake lever will be a lot greater than the original spec. | ||
| Puddlepirate |
Thanks a lot, Jon. I was asking because I'm fitting the 9/16" master cylinder from a Harley to the Buell XB front caliper. I've got a pic of my project in my profile. Thanks again! | ||
| Justin_case |
You're gonna lose a lot of power going to a larger master cyl. | ||
| Puddlepirate |
Will the 1/16" change make that much of a difference? Wouldn't the larger master cylinder move more fluid, resulting in higher pressure and more braking power? Bigger bore=more fluid=better braking? Maybe I'm backwards here. | ||
| Al_lighton |
It's all about piston AREA ratios, not diameter ratios. Hypothetical scenario with imaginary numbers, working backwards from your caliper. Say you need 100 pounds of normal force on the brake pads against the caliper to generate your stopping force. Say that you have 1 square inch of piston area at your brake caliper, and 100 PSI in the brake fluid. Up at the master cylinder end, you create that 100 PSI. If you had a 1 square inch MC piston, you'd have to put 100 lbs on it to get 100 PSI in the fluid. But if you had 1/2 square inch of piston area, it would take only 50 lbs of force to create 100 PSI in the fluid. But of course, if you have a 1/2 sq. in. piston, a given displacement of the piston will only move 1/2 of the volume of brake fluid as the 1 sq. in. piston. Calculate the area of a 1/2" piston and a 9/16" piston (d^2*pi/4). The area ratios change more than you might think for that little 1/16". Just like lever systems, there is no free lunch. You can always trade force for displacement. A smaller piston will generate more pressure but move less fluid for a given input force and displacement. A larger piston will move more fluid but generate less pressure. | ||
| Al_lighton |
BTW, if you look at modern radial MC's, you see MUCH larger piston diameters, like 17 or 18mm diameter instead of 12 or 13mm diameter. But the reason they work is because the physical configuration/orientation of the master cylinder relative to the lever lets the manufacturer create much higher mechanical leverage ratios against that piston. The hand lever is about the same length as before, but the distance from the lever pivot to the piston actuation rod is tiny relative to the old style MCs. This results in very high piston forces capable of generating the same fluid pressures with a larger piston. I just put a Nissin Radial MC on my Uly, and the combination of the more mechanical leverage with a bigger piston provides better feel, IMHO. | ||
| Puddlepirate |
Excellent info Al, thank you very much. I managed to get my hands on a front master from a 2004 single disc XL, which is 1/2". I just found out that 04+ single disc Sportsters use the 1/2" master. No other Harley uses 1/2". Thanks to all for the info, I can't imagine what could have happened had I gone with the 9/16" bore master cylinder. | ||
| Eboos |
I just put on the radial MC that Al uses and sells on his site. I installed it on my M2. It installed easy and accepted the stock banjo bolts (I used an XB bolt with a 14mm 6pt head instead of the stock one with a 3/8" 12pt head). I did have to rotate my starter switch and throttle assembly so that the throttle cables cleared the banjo. I also built my own brake line with 2 35 degree fittings and a 30" line (same length as stock, a stock line from a XB12S should work). The brake light switch plugs right up. Bleeding the system was pretty easy since there is a bleeder on the MC. Lever pressure feels a bit firmer then the stock one. I am going to ride it today for the first time, I just finished the installation last night. I'll post how it goes. | ||
| Mtg |
So nobody has answered my question the pirate racing pages, so... Does anybody know the diameter of the XBRR master cylinder, and whether it has a brake light switch? A picture would be super as well. I'm looking to put a bigger master cylinder on my XB9R with the stock caliper (I like a hard pull on the brake lever) and the stock system takes way too little effort for my tastes. Thanks. | ||
| Mtg |
I have a radial mount front master cylinder on the way from a 2006 GSXR 600/750. It's 3/4" diameter and will make the lever quite a bit stiffer. The math says 2.3 times harder lever pull, assuming the same leverage ratio. I'll see how it turns out. Install updates to follow... | ||
| Vagelis46 |
I have installed a conventional Nissin 14mm master cylinder. It was a good move. There is an improvement to the "feel" and to the braking power, but I always use 3-fingers on the level. Unfortunately I do not think you can use 2-fingers with the ZTL. Also with the 14mm, the level do not get soft after hard use, as the 1/2" did. The GFA345HH from EBC, are really helping the ZTL to perform OK with no overheating issues. | ||
| Vagelis46 |
The good thing with the Nissin conventional 14mm master cylinder, is that it is very easy to find, and very cheap. I got mine for free, from a friend with a bike using 2 x 4pot calipers (Triumph Speed Triple). He upgraded to a Nissin radial 17mm, so I got the 14mm. It is an instant improvement. | ||
| Mtg |
2 fingers with the ZTL? You may need to do some hand exercises if you can't stop the bike with 2 fingers. I switched mine to a 3/4" (19mm) master cylinder, combined with the change in leverage, I'm at about 15 - 20% HARDER pull on the lever than stock and I've used one finger on the front brakes threshold braking at the end of straights at trackdays. That mod was pretty good for brake feel. The GSXR master cylinder also has a bleeding port on it, which makes removing bubbles at the top of the system very easy. By the way, if you switched out to a 14mm m/c, the stock is already 12.5mm. That's barely a change at all, unless the leverage is different. (Message edited by mtg on October 15, 2007) | ||
| Gotj |
I realize that this thread is about front brakes so pardon the hijack attempt. I have an 06 Uly and I'm interested in stronger rear braking. One reason is that I have two other bikes which have stronger rear brakes and when I get back on the Uly, I have to reprogram my braking technique. BTW, I will not re-work the other two bikes to get Uly-like rear brakes. What is the reasonable and straightforward solution? | ||
| Vagelis46 |
Gotj, I am sure I have seen a 2-piston rear caliper, sold for the XB. Mtg, "2 fingers with the ZTL? You may need to do some hand exercises if you can't stop the bike with 2 fingers." It is not just me to say this. There are also the UK's PB journalists, that said that after a 1-2 hard laps, it was very hard to stop the XB12R, due to brake fade. In these situations 2-fingers is out of the question. You say that 2-fingers is more than enough. You are either not pushing as hard as them, or you have found a perfect pad-fluid combination that I would like to know, or you have gorilla's forearms. | ||
| Mtg |
Well, I normally use 2 fingers braking at trackdays, and the back wheel is barely on the ground (and sometimes comes off the ground a little). I'm riding with stock brake pads (not for long), BUT I did put in race grade brake fluid (Galfer with a 600F dry boiling point) and I am very careful about bleeding ALL air bubbles out. The GSXR m/c helps with the bleeding with the bleeding port on it as well. In the short time I've owned my XB9R, I've put it to the test at Miller Motorsports Park and Pueblo Motorsports Park. Both days the brakes held fade free all day with the above conditions. I did notice on my CBR (which was a little prone to have brake fade) that the faster your lap times, the less brake fade you get  (Message edited by mtg on October 15, 2007) | ||
| Bleblanc03 |
If I install a 14mm master cylinder (from either a pre-radial Yamaha R1 or a Triumph) should it be a bolt-on upgrade? I imagine it will fit 7/8" bars, but will my banjo bolt just fit right on? (Message edited by bleblanc03 on April 27, 2008) |
