Optimal master cyl size for AP caliper

[Fast Eddie]

Can anyone tell me what the optimum master cylinder piston size is for use with a single fitment dual piston AP racing caliper ?

 

[Nortoniggy]

Mine is sleeved to 13mm and I use a standard disc. It is a very good brake. Plenty of power and feel. The standard master cylinder had a very wooden feel.

 

[kommando]

The AP pistons are a different size from the Norton Lockheed so for the 27:1 ratio you need a smaller piston that the 13mm, can't find my calcs but from memory it is either 12mm or 11mm. If you calc it yourself you are looking for the mm2 ratio to be as close to 27:1 you can get.

 

[L.A.B.]

Front Master Cylinder Ratio Chart

 

[MichaelB]

Pretty sure the AP caliper is 41mm.
At 27:1, aligns up with what Kommando commented about 11-12mm.

 

[Fast Eddie]

Thanks all, I had seen that chart recently, it does indeed show that for a twin 41mm piston caliper, 11mm is the closets to optimal.

But (to my totally ignorant mind) 11mm seems so small !

The ‘correct’ AP master cylinder for a single disc (which is no longer available) is .625” or 15.875mm… so a LONG way from 11mm.

However, the last time I used one of those .625 master cylinders, I do not recall it being great for feel !

Has anyone here actually tried an 11mm master cyl with a twin 41mm pot AP caliper ??

 

[MichaelB]

Never to old to learn.
I've read this before, it was nice to have a refresher.

Vintage Brake Tips & Tricks

 

[kommando]

I have a master cylinder sleeved to 11mm on the shelf, not tried it yet. I expect the issue will be the lever will be back to the grip before the brakes are fully on. There is a later version of the 27:1 calculator which includes the lever ratio. Sure I posted that a long time ago when FE was inquiring about radial master cylinders or some such modern upgrade.

Here it is

Post in thread 'Brakes, old or new'

May 4, 2024

"Radial masters have a different calc for the magic piston diameter but the same principle means the diameters need to differ too."


Please say more on this.

The lever pivot orientation to the piston, also part of the "mechanical advantage" equation, I assume.

I forget a lot lot as I move from project to project so its a bit hazy, I did investigate Radial master cylinders as part of upgrading an Aprilia RSV1000 and there are calculators out there for selecting the right piston diameter which are more extensive than the simple 27:1 ratio from Vintage Brakes. These take into...

• kommando

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[Fast Eddie]

I have a master cylinder sleeved to 11mm on the shelf, not tried it yet. I expect the issue will be the lever will be back to the grip before the brakes are fully on.

That’s kinda my fear also.

FYI this job doesn’t involve a radial MC.

I have a 13mm Brembo on the shelf, and I know that worked superbly with a 4 pot caliper. Based on your calculations comparing a 4 pot to a bigger piston AP twin pot, it should work well, so I’m thinking I’ll try that first.

Steve Borland also reported a 13mm working well with a single AP.

I’m just not looking forward to bleeding it, I seem to recall that being something of PITA…

 

[B+Bogus]

I haven't tried an 11mm master cylinder, but the RGM 13mm re-sleeved Norton-Lockheed master cylinder works really well with an AP Racing CP2696 caliper.
Great feel, and tyre-squealing power.
Personally, I wouldn't 'feel' the need to go any lower.
My old Rickman Trident had the '70s setup; AP-CP2195 caliper and CP2215 master cylinder, the same as the early Ducati 750GT. It was utter rubbish. '70s pad material didn't help, but it was like squeezing a brick.
Strangely, the rear brake (same geometry) was pretty good. It needed to be
The Production Racer parts listing shows the same Master cylinder for single and twin disc applications. I have the same geometry (5/8" master cylinder, twin CP2696 calipers) on my T140 and it's great, just like modern braking performance.

 

[Holmeslice]

That’s kinda my fear also.

FYI this job doesn’t involve a radial MC.

I have a 13mm Brembo on the shelf, and I know that worked superbly with a 4 pot caliper. Based on your calculations comparing a 4 pot to a bigger piston AP twin pot, it should work well, so I’m thinking I’ll try that first.

I’m just not looking forward to bleeding it, I seem to recall that being something of PITA…

Edward Rapido,

13mm Brembo is magic with a single CP2696. Proof is in the eating. They are the easiest to bleed of any M/C if you ask me. And if you want to get really punk rock you an get a lever with an adjustable ratio, and change it during the race, as I do.

 

[Fast Eddie]

Edward Rapido,

13mm Brembo is magic with a single CP2696. Proof is in the eating. They are the easiest to bleed of any M/C if you ask me. And if you want to get really punk rock you a get a lever with an adjustable ratio, and change it during the race, as I do.

Thanks a lot Kenny, that’s just the kinda first hand punk rock experience I was hoping for !

 

[Holmeslice]

BTW - I'm talking about a Brembo square 13mm reservoir M/C like the bevel Ducatis ran, not one of those New Wave radial masters the kids are into these days.


-KC

 

[Fast Eddie]

BTW - I'm talking about a Brembo square 13mm reservoir M/C like the bevel Ducatis ran, not one of those New Wave radial masters the kids are into these days.


-KC

Yessir, that’s what want.

I’ve got a new wave radial on the punk rock Seeley and it’s sweeet!

This is for a job where I’m after a more trad punk set up.

 

[acotrel]

I use two AP calipers with a master cylinder which was designed for one. I use my forefinger to operate the brake and the rest to operate the twin cable quick-action throttle. The main thing with the AP calipers was the pads - not the hydraulics. The pads in my front brake are the early asbestos pads - anything else did not work. My front brake always works with one finger - even if it is a drum brake. If you need to move your hand to apply the brake, you might be too late. I think some people prefer to grab a handful of brake - you would not do that on any bike which I have built. Quik response is important. Drum brakes cannot be used in the middle of a corner - discs can.

 

[SteveBorland]

I use two AP calipers with a master cylinder which was designed for one. I use my forefinger to operate the brake and the rest to operate the twin cable quick-action throttle. The main thing with the AP calipers was the pads - not the hydraulics. The pads in my front brake are the early asbestos pads - anything else did not work. My front brake always works with one finger - even if it is a drum brake. If you need to move your hand to apply the brake, you might be too late. I think some people prefer to grab a handful of brake - you would not do that on any bike which I have built. Quik response is important. Drum brakes cannot be used in the middle of a corner - discs can.

I have (I think) a 5/8" Lockheed master cylinder with 2 AP calipers on my Ducati 750 bevel, and this is extremely effective. When I was doing track days with this bike, there were very few (if any) other bikes who were out braking me, and I don't consider myself as an especially good rider.

Really good feel, possibly a bit much brake for such a light bike, but it seems to work very well indeed.

I have an adjustable Lockheed 5/8" master with the same 2 AP calibers on a T160, but I've yet to try this. Don't ask why not....

 

[Andy Higham]

Many years ago I had a Suzuki GSX1100, the brakes were appalling. Pulling the front brake lever produced very little braking, harder pressure on the lever (white knuckles) produced some braking but the wheel would lock ie no control.
I changed from a 5/8" master cylinder to a 14mm and the braking improved, i had complete control

 

[Onder]

Cannot remember if it is 12 or 13 mil but probably 13. Works a lot better than the stock AP monster for certain.
Fair amount of lever travel almost goes to the grip but I prefer that anyway. Got it off ebay it wasn't expensive.
It says 'Brembo' but one never knows.

 

[linker48x]

If the question is, has anyone used an 11 mm master cylinder with a 41 mm two piston Lockheed, the answer is, I used that combination on my AHRMA 750 sportsman Triumph 750 in a Redline frame for nearly 25 years, and on my AHRMA F500 RD 430 for 10 years, and then I stopped racing or I would still use that combination on the track. I still use it on the street these days on my Norton Commando with a 12 inch floating disc, and on my Triumph T140D with floating disc. They have all worked really well. My usual answer to this question is to include the link to the Vintage Brake table, so you can see what an expert recommends, but that appears up above--Michael Morse knows brakes and knows what he is talking about. The lever is a little soft, with a woven stainless line, if you are used to old fashioned British disc brakes with a large master cylinder, the feel is about like my R-1 race bike, but I have many times picked up these bikes on the front wheel with the brakes, so the braking power is high, and the feel is also very good. You should use whatever you have tried and like, and if that is a 5/8, or 12mm, or 13 mm, whatever, you should use it. Use what works for you, change it only if you are displeased with what you have, but that is what I have used for many years. But one thing---if the lever is going to the bar with the 11mm, or any combination, there is something wrong, and you need to fix it--with stainless braided line, and careful bleeding, this should not be happening.

 

[Fast Eddie]

Cannot remember if it is 12 or 13 mil but probably 13. Works a lot better than the stock AP monster for certain.
Fair amount of lever travel almost goes to the grip but I prefer that anyway. Got it off ebay it wasn't expensive.
It says 'Brembo' but one never knows.

I’m pretty sure they don’t make a 12mm, in that design at least, so it’ll most likely be a 13. It should say PS13 on it somewhere.

BTW, those two tiny unused holes are for a super neat brake light micro switch.