13mm Master Cylinder Upgrade (Again)

Before I pull the trigger and order the 13mm master cylinder from Andover Norton I would like to know why the upgrades are all 13 mm and not 12 mm.

The stock Norton caliper has 2 - 44mm pistons. I have read the ideal ratio is 27:1.

According to the chart on Vintage Brakes website a 13 mm master cylinder provides a ratio of 22.91:1 while a 12mm master cylinder provides the "near perfect" 26.89:1 ratio

What gives?

27 is not ideal ratio just where moderns settled for general public as a compromise of caliper pressure developed vs the distance the lever must move towards grip to supply the volume needed to move caliper pads enough. Lockheed seleeved 12 mm lever travel may be a factor if ease of just 2 outer fingers means having to curl in enough requires re-grip positioning of hand on throttle. Kind of annoying to be braking a squeal with ease but lever travel requires some throttle twist so engine rev's w/o load till releasing hand pressure which messes with maintaining desired slowing with an interval of free wheeling to grab well again with slightly more tendency to over do as a bit slower than just prior. If all goes well may never care. If any engine drag being used prior to needing a good quick brake let go grip before braking or tends to speed up till ya do.

1/2" (12.7mm) or 13mm is a common size for mastercylinders. 12mm is not.

madass140 said:

1/2" (12.7mm) or 13mm is a common size for mastercylinders. 12mm is not.

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So what you are saying is it’s a matter of availability and there just aren’t many 12mm master cylinders available.

arch said:

So what you are saying is it’s a matter of availability and there just aren’t many 12mm master cylinders available.

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Well, not just that, no. As hobot pointed out, the lever travel is markedly increased. A smaller piston must necessarily travel farther down the bore, and the lever closer to the grip, so as to move the same amount of fluid to the caliper. In fact, I wd hazard a guess, and say that a 12 mm bore with an old ballooning rubber hose, and little pad material left, you might even pull that lever all the way to the handlebar before you reached max pressure. That's not gonna brighten your day.

By my limited math skills, I get 33% more movement needed for 13 mm, compared to the stock 5/8.
Again compared to stock, a 12 mm needs 43% more movement.
Cross sections:
5/8" bore - 198 square mm
13mm - 132.7 sq mm
12mm - 113.1 sq mm

Mr. Rick said:

Well, not just that, no. As hobot pointed out, the lever travel is markedly increased. A smaller piston must necessarily travel farther down the bore, and the lever closer to the grip, so as to move the same amount of fluid to the caliper. In fact, I wd hazard a guess, and say that a 12 mm bore with an old ballooning rubber hose, and little pad material left, you might even pull that lever all the way to the handlebar before you reached max pressure. That's not gonna brighten your day.

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I do not think pad thickness has anything to do with excessive lever travel, as the wearing pads will always be a certain distance away from the disc. Now an even a slightly wobbly disc knocking the pads away, that is a different story. I would say your decision on the non sleeved brand new 13mm Andover Norton MC is a great one (unless you go full blown big sized non OEM Norton aftermarket).

Thank you for all the input.

The discussion on lever travel was interesting.

I am planning on keeping the stock caliper and go with the Andover Norton 13mm m/c

If I decide go with an after market disc / caliper at a later date I am certain there will be a buyer for my improved stock set up.

Contrary to hobot’s comment, 27:1 is the ideal ratio for a 2 piston single caliper brake. I had 27:1 ratio setup and it performed light years better than the grossly oversized 5/8" bore of the stock master cylinder. 23:1 will be a big improvement. 27:1 is just a little bit sweeter. The information posted on Vintage Brakes website is dead on.

13mm bore, upgraded Ferodo pads, Blanchard-ground disc, and a stainless braided/Teflon jacketed hose took the fear out of panic stops from days gone by. Now, if I could just keep the idiot drivers away from me...

Nathan

I settled on a 1/2" diameter (12.7mm) because I could get the seals from Harley. Rebuild kit is $16 at HD dealer.
Before I finalized my design I put a 11mm Yamaha MC on for a try. It worked great, but I decided that 1/2" would be enough.
Anything less than the 5/8" stock will be an improvement. It is not critical from my experience.
Jaydee

I have the AN upgrade with a Venhill hose with the stock caliper and it works well for me.

arch said:

Thank you for all the input.

The discussion on lever travel was interesting.

I am planning on keeping the stock caliper and go with the Andover Norton 13mm m/c

If I decide go with an after market disc / caliper at a later date I am certain there will be a buyer for my improved stock set up.

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That sounds like a great plan, Arch. If not for cost, and having already bought the madass kit, I'd do the same.
I think we wd all agree that a braided hose is pretty much mandatory as well, and especially so if the original is still fitted. Big payoff for few dollars,

getting back to EXCESSIVE LEVER TRAVEL, can the lever have a dab of weld added on to the point where it pushes the master cylinder piston? Is the aluminum lever weldable? The kit I am dealing with has the piston made of Delrin.

To add length to just the lever piston contact is risking heated brake fluid to cause un-releasable lock up on even slight brake grip. Lever bending or made like RGM race level might work if hand long enough to keep some brake covering grip. Some modifiers have added adjustable set screw to adjust lever position. Modern solution is more smaller calipers with less volume needed to move than cavernous Lockheeds. Also smaller pads in a row used to just heat narrow rim of 'bigger' rotor which distorts less than heating over wider band like vintage issued.

When I got into Commandos little to none of the current upgrades available so most my mods were on factory parts. If not sticking to obsolete parts then plenty of proven bolt on better brakes to spend on. All's I can add is if ya think 90 or 100 front tires is adequate and slightly lighter feel more vital - I fear for your safety in a panic stop.

seattle##gs said:

getting back to EXCESSIVE LEVER TRAVEL, can the lever have a dab of weld added on to the point where it pushes the master cylinder piston? Is the aluminum lever weldable? The kit I am dealing with has the piston made of Delrin.

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Besides having been warned away from doing anything except polishing the contact points of piston and lever, it seems to me that this wd not help anyway. There is a minimum volume of fluid that must be moved. The primary cup (retracted, at rest) is positioned just short of the bypass port so it begins working immediately. So I think if you "cheat" the piston forward, you might run out of travel before enough fluid has been moved.
Thanks to L.A.B. for showing me this:
http://www.slideshare.net/shaikusmanshag/5-classification-of-brakes


Also, this is a good place to note that my calcs above relate to piston travel, not necessarily directly to lever travel. There is of course a pivot and a lever involved and I'm not smart enough to figure out if those two are correlated as a linear function. It may well be that the piston moves much faster (or slower) as the lever comes back.

I'm adding to this post 'cause I learned something that might help somebody someday:

With a stock 5/8 bore, the piston actually moves very little. About 1/4" or 6.3 mm (ALL numbers her are approximate)

Lever movement to lockup (measured halfway down the lever, about 3" or 76mm from the pivot bolt) was about 3/4" or 19mm with a stainless hose and no leaks. It rotates around the pivot bolt about 12°.
And this takes into account slop in the system, directly measured with a working brake.


Using an additional 35.65% based on cross-section difference (and assuming a linear correlation) we get for a 1/2" bore:
Piston movement of about .34 inch, 8.6mm
Lever travel of 1" or 25.8mm and about 16.3° of rotation

So I now conclude that (unless you have VERY large grips installed) increased lever travel is a relatively small consideration when going to a smaller MC bore, if all the parts are working properly.

I've got the 13mm and the lever travel is much more than standard, more feel as well. I think the 12mm MAY have too much lever travel. Brakes are brilliant!

FWIW, I have a sleeved OEM MC and a CNW Brembo masterclinder. The sleeved OEM is a notable improvement over stock BUT the CNW Brembo MC, a SS brake line, and Ferodo pads on the OEM caliper/disc will stop the bike with the same authority and feel of most modern machines. Of course, the Brembo does not look stock and if that's a big consideration, then it's a non-starter. But you can buy a mounting plate from CNW that allows the MC to bolt to the OEM switchgear. That method doesn't look so "incorrect" as having to replace the OEM switchgear with "modern" stuff.

I have routinely switched from the sleeved OEM to the Brembo and back because when I bought the CNW, they did not have the adapter plate; you had to replace the OEM switchgear. CNW sold some Honda (I believe) switchgear for that purpose which is what I used. I loved the braking performance of the the Brembo MC but didn't care for the Honda switchgear. SO I would dislike the look and periodically put the OEM sleeved MC/switchgear back on, then hate the brakes and, a month or two later, put the Brembo back on. IMO the adapter plate now available solves most of the problem though, of course, the Brembo is still not "stock."

On a Commando with a Oem-size front tire (4.10-19) with the Brembo MC and stock caliper with Ferodo pads, and a SS brake line, the braking is limited by the front tire. IOW, adding dual discs is totally unnecessary; you will get no additional stopping power. The Brembo MC/stock caliper can lock the front wheel; adding another disc/superduper calipers will not add any performance to the mix on a stock -wheeled/tire bike.

Oh, FWIW, my sleeved OEM caliper failed once and I had to send it back to the company to be resleeved. The sleeve shifted or something like that - I don't recall - but it gave me bit of an uncomfortable feeling about sleeving...

MexicoMike said:

.................. but it gave me bit of an uncomfortable feeling about sleeving...

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+1

I made my own sleeve and JB welded it in. It will not shift.
Jaydee