brake master cylinder diameter reduction

Appologize if this is redundant, but did a subject search and got nothing. From Graeme's string on drilled disk, wanted to start this new so as not to hi jack his subject.

I see Fair Spares America lists 13mm sleeve for the master cyclinder. If I read vintage brake's table, looks like to get a 27:1 optimum ratio with the stock 44mm piston in the Lockheed, a 12mm master cyclinder is the right size. What suppliers have 12mm sleeving available?

A web search says RGM do a 1/2 inch. Close enough to 12mm.

And Rocky Point Cycles can do a 11mm Magura with switches. (sounds interesting )

Regards Graeme.

GRM 450 said:

A web search says RGM do a 1/2 inch. Close enough to 12mm.

And Rocky Point Cycles can do a 11mm Magura with switches. (sounds interesting )

Regards Graeme.

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1/2 is closer to 13mm than 12mm, no? Still has to be better than stock.

Gremica makes a 11mm master cylinder. I ordered one from a dealer who sold MZs. IIRC, it was from the MZ 250 motard. Fitted it to a Grimeca caliper, I believe it's 41mm 2p, from Clubman Racing. Makes for an excellent stopper. The ratio is 27.79

I am with Jim on this one. (I took his advice).
I was told RGM is 13mm, but 1/2" is 12.7
I have tried a bike with their conversion. It is OK, much better than original 5/8", but still a bit wooden to me.
11mm is much better, gets the ratio closer to 29:1.
(We are talking about matching this to a twin pot 41.3mm piston diameter caliper here).
I used an AJP unit which I bought second hand....they are used on trials bikes and some cheapo scooters. It is a really neat unit with a brake light switch and a small alloy reservoir which I have grafted to the original switchgear. It cost me £5 and transformed my braking. I wish I had not spent all that money on fancy disc upgrades now

You can buy any number of 11, 12, or 13mm mastercylinders from Magura, Brembo, Nissin, etc. and they will all work. However, you will lose your switchgear and need to rewire the left switch and/or lose a hi/lo switch or turnsignals. Or replace the switchgear. I have done both a 11 mm Magura and 12 mm Brembo. Not a tremendous difference in feel. Both good

Al Miles does a complete 13 mm sleeve on an exchange basis for the stock Norton master. These are available through a number of excellent dealers, such as Rocky Point and British Bike Connection. I have used these with excellent results. As far as I know there is no kit for an 11 or 12 mm sleeve.

The 27:1 figure is Mercury Morse's own preference. It gets you close and the optimum brake feel is somewhat personal. Some like a firmer, more wooden lever while others like a softer, spongier more progressive feel.

Ron L wrote:
You can buy any number of 11, 12, or 13mm mastercylinders from Magura, Brembo, Nissin, etc. and they will all work. However, you will lose your switchgear and need to rewire the left switch and/or lose a hi/lo switch or turnsignals. Or replace the switchgear. I have done both a 11 mm Magura and 12 mm Brembo. Not a tremendous difference in feel. Both good

Al Miles does a complete 13 mm sleeve on an exchange basis for the stock Norton master. These are available through a number of excellent dealers, such as Rocky Point and British Bike Connection. I have used these with excellent results. As far as I know there is no kit for an 11 or 12 mm sleeve.

The 27:1 figure is Mercury Morse's own preference. It gets you close and the optimum brake feel is somewhat personal. Some like a firmer, more wooden lever while others like a softer, spongier more progressive feel.
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Thanks Ron,

I finally understand what "wooden feel" means with your comparison to "spongy". OK, my stock '72 disc setup is wooden feeling. It work pretty well though. I had Phil at Fair Spares America do a 13mm modification to the master cylinder on my '74 JPN. I didn't notice it was any different than the stock brake on my '72 roadster. That's why I'm asking about a 12mm sleeve.

To give you an idea about the difference in 'feel' from my 5/8" (15.875mm) stock piston and my 11mm one, I could grab the lever with 4 fingers and pull as hard as I could when the bike was stationary, and the lever would not move at all from the original 'grab' position. On the road you needed all four fingers and the bike would still not stop.
With the 11mm piston you can grab the lever and pull it right back to the bars, no problem, when stationary. On the move you need only two fingers, with the increased braking coming in progressively as you pull in more. You get nowhere near the lever touching the bars. I now can feel fork flex. Never felt that before...
The pads (EBC Kevlar) need to be warm to get the best out of them, and my brake is still poor in the wet, especially when cold, even with a drilled RGM bigger disc. I hear there are better pads available Ferrodo Platinum, I think.

RonL
I took the back half of the clamp and threw it away, and milled 6mm off the master cylinder half. I then made two adaptor plates that had the hole pattern of both the original switchgear (4 holes) and the new master cylinder (2 holes)in. This allows the use of the original switchgear. I will post a photo...it still needs 'final fettling'.

I took the back half of the clamp and threw it away, and milled 6mm off the master cylinder half. I then made two adaptor plates that had the hole pattern of both the original switchgear (4 holes) and the new master cylinder (2 holes)in. This allows the use of the original switchgear. I will post a photo...it still needs 'final fettling'.

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If I can't do it with a hacksaw and file I'm screwed! I like the idea though!

I just installed the Andover Norton 13mm master cylinder kit. It's a Grimeca cylinder (I'm pretty sure) adapted for use with the Lucas switchgear. It's not a sleeved Lockheed cylinder.

Personally, I am quite happy with it. The kit came with a brake-light switch and braided steel brake line. Depending on exchange rate, it can be cheaper than the 13mm set up from Al Mile's vendors, which is why I bought it. Also, I understand that the sleeved Lockheed master cylinders can be difficult to bleed effectively. The one I bought from Andover gave no problems.

Based on the feel of this 13mm set-up I would guess that an 11mm master cylinder would be too "soft" for my taste.

Corona850 said:

I just installed the Andover Norton 13mm master cylinder kit. It's a Grimeca cylinder (I'm pretty sure) adapted for use with the Lucas switchgear. It's not a sleeved Lockheed cylinder.

Personally, I am quite happy with it. The kit came with a brake-light switch and braided steel brake line. Depending on exchange rate, it can be cheaper than the 13mm set up from Al Mile's vendors, which is why I bought it. Also, I understand that the sleeved Lockheed master cylinders can be difficult to bleed effectively. The one I bought from Andover gave no problems.

Based on the feel of this 13mm set-up I would guess that an 11mm master cylinder would be too "soft" for my taste.

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Just deciding on a master cylinder it upgrade, how well finished/made is the Andover kit?

I have a Grimeca caliper with standard cast iron disc & s/steel hose on my 850. I also have the RGM sleeved Lockheed m/cyl. I done this several years ago when RGM supplied the parts as a kit, I had to Araldite the sleeve into the original bore and drill the by-pass hole, I don't think they supply it like this any more, you have to send it to them to do I think. The sleeved m/cyl was the last and most effective thing I done to improve the brake.