Front Master Cylinder

rbt11548 · Feb 7, 2009

Hi All, There has been mention of different types of front master cylinders from different manufacturers for the Commando, I have fitted the RGM Grimeca disc and caliper to mine and was wondering whether to go down the route of getting the Norton,(Mk3), one re-sleeved or replacing it altogether. There are many kinds for sale, even 2nd hand, which after new seals and a rebuild would possibly do.
Any ideas?

bill · Feb 7, 2009

I believe that the grimca and ap Lockheed caliper have the same size pistons (41MM). if so than a stock master cyl with the 13MM sleeve or any other master of that size will make a good brake but an 11MM master will be much better. the 13MM will give a ratio of 19.9 which is below what vintage brake recommends while the 11MM is at the top at 27.8.

windy

JimC · Feb 7, 2009

I have a Grimeca caliper with a 11mm master cylinder and a 12" floating disc. It approaches the performance of a twin disc setup. You can add all the high dollar brake goodies, but if you don't get the 27:1 ratio your brake performance will be lacking.

rbt11548 · Feb 7, 2009

JimC said:
I have a Grimeca caliper with a 11mm master cylinder and a 12" floating disc. It approaches the performance of a twin disc setup. You can add all the high dollar brake goodies, but if you don't get the 27:1 ratio your brake performance will be lacking.

Hi Jim , is it the Grimeca master cylinder you have or another type?
Thanks
Robert

JimC · Feb 7, 2009

Yes, it's a Grimeca. It's one with a square reservoir and a mirror mount. It's from a MZ 250. I'd say it was circa 2000.

Ron L · Feb 7, 2009

Robert,
A major part of the decision on whether to sleeve the stock master or go to a Grimeca, Magura, Brembo, etc. is whether or not you want to keep the stock switchgear. Changing switchgear would also mean you would need to change the gear on the left handlebar and come up with a clutch lever to match your new brake lever, depending on how important aesthetics are to you.

As Windy points out, going the sleeve route with your caliper gets you to only 19.9:1. Going to a 4 X 32mm caliper gives you 24.2:1 with the sleeved Norton master, but you will need to adapt the caliper to your fork. JimC's solution of an 11mm master will get you where you want to be at 27.8:1 for the most effective brake, you will just have to deal with switchgear and clutch handle.

Keep in mind other factors, like disc diameter, wheel diameter and lever mechanical advantage also factor into this. The lower (numerically) you go on the ratio, the more wooden the feel. Too high and the brake can feel mushy.

JimC · Feb 7, 2009

I saved the stock switch gear. I fabricated a plate with a U in it for clamping to the handlebar. I also replaced the clutch lever with one from a MZ and did the same for the right side switch gear. Someone with a mill and a billet could do better.

rbt11548 · Feb 8, 2009

Ron L said:
Robert,
A major part of the decision on whether to sleeve the stock master or go to a Grimeca, Magura, Brembo, etc. is whether or not you want to keep the stock switchgear. Changing switchgear would also mean you would need to change the gear on the left handlebar and come up with a clutch lever to match your new brake lever, depending on how important aesthetics are to you.

As Windy points out, going the sleeve route with your caliper gets you to only 19.9:1. Going to a 4 X 32mm caliper gives you 24.2:1 with the sleeved Norton master, but you will need to adapt the caliper to your fork. JimC's solution of an 11mm master will get you where you want to be at 27.8:1 for the most effective brake, you will just have to deal with switchgear and clutch handle.

Keep in mind other factors, like disc diameter, wheel diameter and lever mechanical advantage also factor into this. The lower (numerically) you go on the ratio, the more wooden the feel. Too high and the brake can feel mushy.

Hi Ron, I have fitted the 12" floating disc and Grimeca caliper kit from RGM which also comes with braided lines and a lever with a different configuration which is meant to improve leverage, but if the ratio is not changed I can't, as you say, see the lever making a big difference. The switchgear issue is not a big issue for me, as there are a lot of switches that would be useful I'm sure, and I would have the stock stuff here if I decided to change back. In fact I read somewhere on here about a L/H switchgear unit that had all the neccessary buttons on it. I'm sure I could source switchgear somewhere.
As for the master cylinder I was wondering if there possibly a Guzzi, Ducati, Yam, etc. unit that would fit and give me the ratio as they seem to be plentiful on the ground at not too bad prices. As I said earlier I don't mind having to do a wee bit of work on it, replacing seals & servicing it. Running standard wheel sizes.
Thanks

Hortons Norton · Feb 8, 2009

Matt at Colorado Norton Works has Brembo master cylinders and the matching clutch lever, Also switch gear for the left side. The set up looked good to me so that is the route I am going,
When I someday finish this bike (LOL) I will report back on how it works.

rbt11548 · Feb 8, 2009

Hortons Norton said:
Matt at Colorado Norton Works has Brembo master cylinders and the matching clutch lever, Also switch gear for the left side. The set up looked good to me so that is the route I am going, When I someday finish this bike (LOL) I will report back on how it works.

That lot is neat!, it is certainly worth considering, will check it out .
thanks

Ron L · Feb 8, 2009

Is that a Magura clutch lever? That's what I used on my cafe bike. Works nice, but had to redrill the lever to take a Norton clutch cable barrel. (easy mod)

rbt11548 · Feb 15, 2009

Hortons Norton said:
Matt at Colorado Norton Works has Brembo master cylinders and the matching clutch lever, Also switch gear for the left side. The set up looked good to me so that is the route I am going, When I someday finish this bike (LOL) I will report back on how it works.

Had a look on the CNW site, the Brembo master cyl looks good , I noticed it said 13mm, will that give close to the 27:1 ratio that is meant to be the best?

Corona850 · Feb 15, 2009

rbt11548 said:
Had a look on the CNW site, the Brembo master cyl looks good , I noticed it said 13mm, will that give close to the 27:1 ratio that is meant to be the best?

No. It gives 19.89:1.
See the chart at Vintage Brakes site http://www.vintagebrake.com/mastercylinder.htm

rbt11548 · Feb 26, 2009

Corona850 said:
rbt11548 said:

Had a look on the CNW site, the Brembo master cyl looks good , I noticed it said 13mm, will that give close to the 27:1 ratio that is meant to be the best?

Click to expand...

No. It gives 19.89:1.

Hi guys, sorry to labour this a bit, I was trawling the net with regard to the front master cylinder. Tha AP lockheed site has front master cylinders, but the bore size again, is 15.8mm, which wouldn't give, on the RGM grimeca caliper, the 27:1 ratio, but I have noticed various classic racers using them on Nortons fitted with the aforementioned, or Lockheed calipers, (Grimeca is an almost direct copy of the Lockheed), would the braking be improved by fitting a modern master cyl. even although the bore would be about 15mm? The only cyls that seem to be available in 11mm are for smaller trail bikes 175's , 250's etc., would one of those do?

JimC · Feb 26, 2009

A master cylinder doesn't care what bike it's on. The 11mm master coupled with the Grimeca caliper is what I happen to have and it's from a 250cc bike. Excellent stopper. The most important part of a disk brake setup is the ratio of 27:1. You can have twin floating discs with six pot radial calipers, but if the master is not of the correct size it's all for naught.

rbt11548 · Feb 26, 2009

JimC said:
A master cylinder doesn't care what bike it's on. The 11mm master coupled with the Grimeca caliper is what I happen to have and it's from a 250cc bike. Excellent stopper. The most important part of a disk brake setup is the ratio of 27:1. You can have twin floating discs with six pot radial calipers, but if the master is not of the correct size it's all for naught.

Thanks Jim, just wasn't too sure, didn't want to take a chance on getting wrong one and being stuck with it. So you reckon a small Honda or similar cylinder would be fine as long as it's 11mm?

JimC · Feb 26, 2009

Korrecto!

rbt11548 · Feb 26, 2009

JimC said:
Korrecto!

Jim... thanks for putting it in such a way that I cannot be mistaken :lol:

rbt11548 · Mar 2, 2009

On the hunt for a 11mm front master cylinder, would a 10.9mm do? there seem to be a few of those kicking about.
What's 0.1mm between friends? :shock:

cash · Mar 2, 2009

In my early days of messing about with m/c sizes I found the 11mm could be an absolute pig to bleed unless there was enough stroke to give plenty of flow, and for me 11mm gave too much lever movement. I've used 13mm set-up for near 14 years and find it more than adequate, with two fingers I can stand the Commando on its front wheel. (not intentionally I add)
I reckon anything between 13mm and 11mm will be OK but that 0.1 less might be the last straw.

Cash

Front Master Cylinder

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