1973 850 Commando front brake M/C question

I just installed an AN new master and it works well.
There is another advantage (more than the smaller bore that gives more hydraulic advantage.)

The handle moves more than on the stock (squirting brake fluid up out of first reservoir hole) before hydraulic lock occurs that builds pressure to move the pads. This means finger muscles are applying more force due to how the muscles are positioned.

Dennis

NorCat said:

My resleeve Kit failed after 6 years of use.
I am installing a New AN 13 complet New unit now that are available.

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I had an RGM 13mm resleeve kit installed in my original mc of my Roadster 19 years ago. It still works quite well. Never a problem. My more recently acquired Interstate's front brake was just unacceptably bad. I bought and installed a new A/N 19mm mc. It and the resleeved one function identically.
What I'm saying is that while I have had a very good experience with the resleeve, I wouldn't do it again.

MC piston ratios were universally terrible on early disc brakes- my RD350, renowned when new for having excellent brakes, has terrible feedback and feel by modern standards. The change to smaller pistons and less flexible mounting systems (radial master cylinders for example) have resulted in there being more lever travel for a given pressure, such that they are easier to modulate and provide better feedback.

And we all know that….

It’s my belief that this was likely a choice by manufacturers to make the very early disc brakes feel like the drums they were replacing.

Re-sleeving seems like a solid notion to achieve some improvement but the potential drawbacks don’t really align with the cost, especially if a new unit at the “corrected” size is available. I’ve not ridden a Commando before and after such a swap but have done a similar change to my RD400 race bike, going from a 5/8” master (stock RD400f) to a 12mm unit, and the change in brake feel and power was stunning. The RD is equipped with a 3-fin Lockheed caliper, so I would expect the results may be similar with the Norton swap to a 13mm.

In this same vein- my R80g/s has had its brake lines swapped to braided stainless and a large rotor kit installed- and while brake power is now very good the feel is wooden and lever pressure is high.



Unfortunately the master cylinder is built into the throttle assembly, and it’s the smallest piston BMW offered. I’m pondering sleeving it down to a 11mm this winter (from 13mm) to see if I can improve it…. But I might see if I can find a used unit to monkey with and save the original in case I’m unsuccessful.

My Seeley 850 has two steel discs on the front , both with Lockheed AP calipers with asbestos pads. The master cylinder was designed for one caliper. I also have a Yamaha TZ350 twin pull, quick action twist grip. When racing three of my fingers and my thumb grip the throttle and my forefinger operates the front brake. It has to be that way. With disc brakes, the rider can brake anywhere safely. With drum brakes the rider needs to be much more careful. The front brake and the gearbox determine how fast you can ride. Used properly, a slow motor is usually fast enough.
When I sold my Triton back to the guy who had built it in about 1958, the first thing which happened was he phoned me and asked what linings were in the drum front brake. If you grabbed a handful of that, you would probably die. With disc brakes it is usually safe to brake in the middle of a corner - not with a drum brake. Motorcycle road racing is only really dangerous the first time you do it. After loss of ego has happened, it becomes much safer.

Sure, modulation and feedback are the reason discs are so much better- in addition to being fade resistant and utterly predictable- and they have only improved as the piston ratios have been monkeyed with. Acotrel’s distain for drum brakes is understandable and well founded, even though dullards like myself still find them fascinating.

This is a Norton forum, after all- it wouldn’t exist were we not enamored of the old, weird, and obsolete.

Sleeving as a means of repairing or restoring master cylinders has been a pretty standard deal in vintage cars and using it to re-size a motorcycle master cylinder certainly seems like a solid notion. But it can go wrong, and I would agree that one is likely better off with a good non-sleeved cylinder is that’s an option.

I did my own in the end, I tried the RGM but it looked so bad I couldn't face fitting it.
It uses a Honda 12.7mm seal, sleeved master cylinder.

works realy nice.
Fits the exactly the same as the original with the rubber boot etc. and lever position is the same.

I've played with a lot of brake variations over the years including a comedy 6 pot caliper on a big disc and this is so much better.

Elfix said:

Sure, modulation and feedback are the reason discs are so much better- in addition to being fade resistant and utterly predictable- and they have only improved as the piston ratios have been monkeyed with. Acotrel’s distain for drum brakes is understandable and well founded, even though dullards like myself still find them fascinating.

This is a Norton forum, after all- it wouldn’t exist were we not enamored of the old, weird, and obsolete.

Sleeving as a means of repairing or restoring master cylinders has been a pretty standard deal in vintage cars and using it to re-size a motorcycle master cylinder certainly seems like a solid notion. But it can go wrong, and I would agree that one is likely better off with a good non-sleeved cylinder is that’s an option.

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I love the appearance of large drum brakes, but they are not good for racing. They need to be one-finger operation, but they are never as good as twin discs. My T250 Suzuki had a drum brake - during races two-stroke engines heat-up and get slower, and drum brakes heat-up and change. After 5 laps - where are you ? With my Triton 500, my nightmares were about being balked in corners. Using a drum brake in the middle of a corner is dangerous if you do not know what is going to do. And if my motor dropped out of the power-band - slipping the clutch would cause the bike to go sideways. I love my Seeley 850 - it never tries to kill me. With twin discs, the brake can be used anywhere - and the strong smooth power-band is lovely. I might be a better rider than many, but I know what pain feels like.
Nobody should ever learn to race by doing what I did. I should have been banned.

Resleeving the master cylinder is better done by a brake shop. I think there are sometimes sharp edges internally which can damage the cup.

Be better to install a new MC with the right size for single disc, lot of options around and better than fixing a 50 year old MC, in fact best thing I ever done was upgrade to a full modern front brake system when my old system failed without warning, that was over 10+ years ago now and when recovering was when I did the full upgrade, now my Norton stops and easy one finger if I want to use one finger.
Full Grimica front brake system was just over $500 all up from RGM and delivered to my front door, 12" floating disc, 4 pot caliber, mounting bracket, SS hose, MC and longer brake lever and no mods needed, fit, bleed, ride, one of many best upgrades to my old Norton and my life is worth the money well spent.
I went through the fixing and rebuilding the old brake system but in the long run the full new upgrade was the best, one day your 50 year old front brake will fail and let you down when you need it as mine did without any warning.

Ashley