Front master cylinder replacement

Simon,

You have to count both calipers i.e. 4 pistons not 2. O8's use a 38mm piston from memory so with a 14mm master cyclinder piston the ratio is 29.47/ 15mm 25.67/ 16mm 22.56. So your on the money I'd say.
You can be pretty sure Brembo get it half right half the time.
Chris
 
Simon

The table that Chris posted doesn't mention lever ratios. It only refers to the hydraulics. From the number that you quoted, I'm guessing you have the standard setup of 38mm P08 calipers and 15mm master cylinder.

Remember that there are two calipers connected to your one master cylinder, so there are 4 active pistons, not two. That brings your hydraulic ratio up to 25.7, which is getting closer to the 27 quoted in the article.

It would be interesting to know who wrote the article. The author clearly states that 27:1 is his personal preference, and from the general context I assume he's talking about track use. He doesn't make any statement about it being generally applicable for road use.

Cheers,
Cam
 
PS: If you don't like lookup tables (and I don't), this formula gives the same result:

Ratio = (S/M)2 x P

Where:
S = slave cylinder diameter
M = master cylinder diameter
P = number of active pistons

However, the table (and the formula above) is limited to calipers with only one size of piston. For calipers with different sized pistons like the Brembo 4-pot, the formula becomes:

Ratio = (P1 x S12 + P2 x S22)/M2

Where:
P1 = the number of slave pistons of diameter S1
P2 = the number of slave pistons of diameter S2
M = master cylinder diameter

Remember to count all pistons in all calipers (with two 4-pot calipers, you'll have 4 of each size)

If you have a 6-pot caliper with 3 different size slave cylinders (if such an animal exists) just add a " + P3 x S32 " term into the parentheses.

Cheers,
Cam
 
Ratio = (P1 x S12 + P2 x S22)/M2

I love engineers. Just goes to show how much real information I've missed out on. That's what happens when you do a degree in the yartz.
You become good at finding shit.

Chris
 
be carefull changeing Brembo disc sizes, especially on 500's the Brembo factory (might) have know what they are up to when they designed and fitted the correct size of 260mm discs but fitting units from a 1000/1200 (280mm) with alloy adapter brackets to move the calipers that little bit further away from the fork legs to compensate for the larger diameter may or may not give the best desired results of feel and modulation.The maker does usually know best (not)
CLEM
 
Here is another long story, originally my Pantah had 38mm Maz forks with the std to Pantah smaller callipers working on 260mm discs,the callipers were mounted with a horrible bodged sandwiched small plate,needed on the 38mm fork.
It worked ok but was shoddy to see.When I fitted the 4 piston callipers to my 3C I decided to fit up the old large 2 piston callipers and master on to the Pantah,I needed a couple of 280mm discs,so now I have my old 3C brakes on my Pantah,looks nicer but does not work much better.It will do for a spare bike but the up rated stuff on the 3C is much better,125cc GP is on,time to go
 
dellortoman said:
It would be interesting to know who wrote the article.
Click to expand...

Cam

I believe it was writ by Michael "Mercury" Morse, who has a web site www.vintagebrake.com. I found the chart there and several other compendia of syllogisms with unverifiable authenticity. What the hell, he sounds like he knows what he's talking about.

Ken

 
Thanks for the comments about ratio's etc. I did not take into account the fact that the two front brakes work in parallel.
That make the front setup 25.67:1 - right on the money according to Mr Morse.

The rear brake is two pistons only with the same master cylinder/piston dimensions, so I assume that the amount of ooomph from the right foot when braking is more than enough to compensate for loss of ratio + you don't need so much force on the rear anyway, otherwise she locks up.

SimonR

SimonR
 
clemtog said:
be carefull changeing Brembo disc sizes, especially on 500's the Brembo factory (might) have know what they are up to when they designed and fitted the correct size of 260mm discs but fitting units from a 1000/1200 (280mm) with alloy adapter brackets to move the calipers that little bit further away from the fork legs to compensate for the larger diameter may or may not give the best desired results of feel and modulation.The maker does usually know best (not)
CLEM
Click to expand...

Clem, ::) you have unwittingly helped me illustrate exactly the point I was trying to make in my original post. The bigger discs I fitted to my 500 have provided a bit more mechanical advantage and improved the effectiveness of the brakes for track use, which is where I intend to use the bike. However the downside is they have increased unsprung weight and increased the gyroscopic forces . The standard brakes on a 500 are nigh on perfect for road use and I wouldn't consider changing the spec on my road bike.

The added weight was a compromise I had carefully considered before making the decision to change the disc size and it underlines my comment that you can't have your cake and eat it, something always have to give. To compensate for the extra weight I opted to fit earlier thin web wheels which are significantly lighter than the OE wheels. All in all it was actually a fairly complex modification, carefully thought through to minimise the downside. My post was simply trying to highlight the need to think things through before acting on impulse. A bit of advice you might do well to consider....


 
Can't you skim, drill and scallop the discs to reduce weight?
I remember Rufus's SFC 750 even had a groove milled in the outer edge of the discs.
If drilled, can you open up the holes more?
Titanium axle?
Unpainted wheels?
Helium in the tyres?
 
I saw that groove on Rufus' SFC , it was a neat idea and I think that it was an original fitment, Marnix will know...
I'll definitely do something with the discs Grant, probably along them lines of what you suggest.
Titanium axles are an obvious route to save a goodly amount of weight but unfortunately are outlawed in classic racing, at least in the UK...
 
I have never seen another SFC with discs like Rufus had on his. Not sure they were standard fitment.

Ok, could you hollow out the standard axle, then plug the ends???
 
Hi all,
For many a year ran (track bike) single 280mm  disc with P08 caliper on the front using std Monty master cylinder on my Binnion framed Monty for many a year.Far far better than the std set up .Braking was more progressive,with feel and bite.Less weight improved the handling also.The std discs are way to heavy,and the calipers tend to bind up on the discs.
In my opinion Bob you should try your front end with just a single disc,your hopefully find you have more feel of what the front end is doing and therefore brake later and longer into a bend ,thus carrying more corner speed;which racing a 500/600 is all about - Corner speed!

Andy
 
Andy, I've always thought your brake suggestion has real merit and I've been intending to try it at some stage. I'll get the bike a bit more settled in and probably give the single disc idea a whizz later in the year. Priorities at the moment are fine tuning the carbs and timing. The bike passed its Mot yesterday and so I can now put some road miles on it to get it fettled.
First impressions are that the Atlas motor is a really nice unit. The bike drives cleanly from 2000rpm and then a big shove comes in the midrange, I've not explored beyond 6000rpm yet out of respect for the brand new motor but I'm going out on it later and might give a few short bursts to see if the revised cam timing allows it to breathe up there. I'm getting quite excited 'cos I'm running it at Goodwood next weekend .....
 
I've mentioned it before somewhere, but after I experienced a scary  front brake failure at 90mph in the fast lane of the motorway on the way back from the festival of 1000 bikes last year(no harm done luckily), and this with a m/cylinder fitted with the seal repair kit 4/5 years before, I've now got the round black grimeca. When I was looking around, Wolfgang didn't do them..i mentioned that i had got one to him...it works much better than my brembo ever did..I run stainless hoses (Andy wagner sourced back in 02.) The downside is that it comes with the mirror hole undrilled...Motomecca did that for me when I whined....and  it comes in my case anyway with a black lever....and since my alloy one wouldn't fit,I bought a new black levered clutch one to match.Not cheap.
I'm no engineer, but I love the quality of the Grimeca..looks sandcast and is one piece with a neat window to check level...not the screw in plastic brembo design. Bought meself a brake beeding suction pump thingy when I couldn't get the fluid in the system..bloody marvellous thing..inspired me to change the rear fluid too....and move on the my Suzuki DRZ...no bother, even for me(and that's saying something!).I seriously can't see the point of 4 pot calipers and the like on the front for the road at least now I have this set up.
Nick7
 
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