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Disc Brake Improvements

a review of correspondence from NOC-L

Improving the performance of Norton front disc brakes
including ideas for fitting master cylinders from other motorcycles

Can the master cylinder be sleeved down?

"Why not sleeve the master cylinder down to the same size as the foreign cylinders which seem to be successful, i.e. about 13mm or ½". The great advantage would be good brakes whilst keeping the original appearance.

Those who know about such things say the sleeving is easy and the piston could be turned down but the difficulty comes in finding the right seals. Has anybody out there looked into this?
"

A do-it-yourself approach to uprating the standard front disc brake

The following is intended as encouragement to anyone who wants to uprate the front brake on a Commando but would like to save themselves some money.

Recently, I decided to uprate That Brake on my Commando and chose to go the AP Lockheed route, since I'd still be able to get the pads at a Brit-bike shop. I couldn't afford the fully-floating disc, or the stage-one upgrades offered by the usual suppliers, so I decided to buy just the caliper first (since it's actually the most expensive item in these kits) then make everything else normally sold with the first-stage kit myself and see if the original disc could be made to do anything quickly (apart from rust). Some had assured me it could. be done, others had assured me it couldn't. Les Emery had said it might, but that his kit was the only one that could do it, if it could be done. I wasn't confident about the adaptor bracket sold by one supplier as it uses slotted holes to take the caliper, so that the one bracket can be used with different sizes of disc. Having the caliper mounted on slots doesn't seem wise to me.

I ordered an AP caliper and master cylinder servicing kit, but in the meantime I'd stolen one of the AP calipers off our Kettle racing outfit which is off the track at the moment (perhaps the safest place for it) and I made up a dummy bracket using some plywood. Plywood is ideal for this job since it's easy to file away at it and get it into whatever shape you want it. It took me two goes to get the shape I wanted - about an hour's work. The finished product was this sort of shape:-

With this, I went down the road and bought a 6" x 4" slab of 3/8" thick alloy billet for about £5 and, using my plywood pattern, hacksawed and filed out a duplicate. This took about two hours - three, if you include time taken to go to the breakers and buy the alloy. Drilling the holes took a little care, it but was done with a hand drill and a vice. The caliper slipped in nicely, but the bracket needed careful spacing to get it aligned parallel with the disc. I checked this using a depth-gauge micrometer, but a vernier with the same facility would be accurate enough. I found that, once aligned, a second spacer-bracket of 6mm was needed behind the first to bring the caliper across so that the pads were equally spaced and would act on the disc equally. The whole assembly went together thus:-

Once the new caliper had been delivered, it was a doddle to assemble the whole lot. Using my new bracket I'd already established (using the AP off the outfit) that I could carefully stretch the short length of solid pipe that runs down to the caliper from the mudguard top-mount bracket on the standard Norton-Lockheed caliper system. This allowed me to re-use my old bit of Goodridge hosing off the original system. I stripped and reassembled the mastercylinder (contrary to what it says in the manual this is a simple one-man job) then bled the system and took the bike out for a spin.

I'd guess I've gained about 15-20% in terms of braking efficiency; although how much of this is down to having a brand new caliper on there, I'm not sure. The EBC pads on the old caliper still had plenty of life in them when I took it off. It was worth it anyway, since I've now got a unique front brake modification for about £40 to £50 less than the standard kits cost. In future, I'll get one of my mates in the engineering trade to mill out shallow hollows in the surface of the new bracket, in mimicry of the two Z-plates that mount the footrest hangers. I reckon that'll make it look a bit more professional.

So there it is; £96.06 for the caliper, and about £6 for materials and maybe 8 hours work, in total. The only disadvantage is that the right hand mudguard stay had to be shortened and now runs from the mudguard to the lower mounting bolt of the caliper. It doesn't look bad and is still parallel with the one on the other side. If anyone else is interested in the caliper bracket I made, I still have the plywood pattern and I can try and see about reproducing it in some sort of transmittable form if you like. Alternatively, I can try to work out the precise measurements all round, including spacer thicknesses, etc. although I think some of the latter are best tailor-made for the bike in question. For instance, my bike's a Mk.lla, but if you have a Mk.lll, with the caliper on the other fork leg, the spacings may well be different. With alloy billet its generally best to rest the piece for about two weeks after working on it, since it's hardness will gradually return to it over this period of time. I didn't do this, of course, but I'm impatient.

D.J. Walker (djw12@leicester.ac.uk) on NOC-L 26th. Mar 1997


Norton Commando Front Brake Improvements

My front brake was improved by reducing the size of the master piston diameter from 5/8" to 14mm some time ago, as described in an earlier article. The change in area provides a leverage increase of 28%, which makes the brake feel reasonable but not as sensitive as the twin leader on my A10 (another make of bike!) which is the 1968 Triumph design. Still the improvement was such that I felt it necessary to fit a fork brace to cure the rapid fork twisting that happened under heavy braking. So what further improvement could be made?

I could have gone to a 12mm master, but didn't really want to because this would increase the brake lever travel. I've ridden a bike with a 12mm master and it was good, but had significant travel in the brake lever - nearly back to the bars. The change from 14mm to 12mm would however give a further 36% improvement, and from the original 5/8", a total improvement of 73%. So what else?

I could have spent money - and fitted a 12" disc, which looks good too. This with no other change improves the leverage by the ratio of the sizes i.e. 12%. The various discs and adapters available don't allow using the original caliper. Stock calipers to suit adapters available are Lockheed and Grimeca; the latter being the least expensive. But the Grimeca and Lockheeds readily available have 41mm pistons, versus the stock Norton 44.5mm. The combination of 12" disc and 41mm caliper piston size gives a leverage decrease of 5%. This change should reduce lever movement, because less fluid needs to move, but the combination will give virtually no change in leverage and hence braking effort. There are however calipers advertised with 'larger pistons', (RGM) which they coyly say are 'better' in their catalogue.

Courtesy of BMS (Wellington, NZ bike shop), the details are as follows:- The usually advertised/available Lockheed is CP2696, 41.3mm, and the Grimeca, readily available, is also 41mm. Apparently Triumph use 41mm. The RGM advertised 'better' Lockheed is CP3697 at 44.5mm. If this is used, then the leverage improvement with a 12" disc is 12%. There are other sources of calipers and discs, e.g. second hand Japanese ones but beware the cost of new discs from the land of the rising sun; also their discs tend to be 5mm thick and prone to distort. Examples of new original Norton discs measured 6.6mm, the same as an original Triumph disc, and the RGM floating 12" is 5.8mm.

Wilwood calipers, made in the U.S.A., are available from Cardwell, 20, Sheffield Crescent, Christchurch (Tel. + 64 (0)3 358 2828) or from 4, Crum Avenue Auckland (Tel. + 64 (0)9 826 0202). The catalogue shows 2, 4, and 6 pots of which the possible one to use is the 4 pot Superlite 11A at NZ$219 but modifications will be needed to suit 6.5mm disc thickness. The piston diameter choice is 44.5mm or 35mm, and the ratio using the 4 pot with the 35mm piston on a 12" disc with the stock master cylinder size is 45%, which sounds good. But as said, modifications are necessary to suit the 6.5mm disc thickness - the Wilwood is for 20.6 mm thickness, and a suitable adapter plate will be needed.

Fair Spares also advertise a 13" floating disc, which alone provides a leverage improvement versus the stock 10.7" of 22%. The actual feel and braking effectiveness is not solely determined by the leverage though; factors such as pad material, pad area and lever shape and probably other things I haven't thought of, also affect this.

However, is the leverage the basic factor? I bought the RGM kit and fitted it. The overall change in leverage given by the 14mm master and 12" disc with 44.5mm pistons is 44%. The good news is - it was better, but not that much better. At first I was disappointed, but a few hard stops from 70 m.p.h. showed it was an improvement. And most important, the first panic stop I did, I didn't lock the wheel although it did make interesting squealing protest noises (both me and the tyre). The bad news, besides the cost, is that it is not a kit in the usual sense of the word. You can't just bolt it on as it requires some modifications to fit.

The pads are accessible from the top, i.e. there is no need to remove the wheel, but need to be reduced in height by 5mm or so, to clear the buttons holding the floating disc. The same buttons brush the inside of the fork slider, and RGM advise 'remove metal from the slider' - brilliant! So I put a 0.5mm washer between the slider and the wheel, which was possible because the wheel has clearance to the offside slider - just. The caliper doesn't clear the mounting plate, and RGM advise removing metal from it. I took some off both caliper and mounting plate, a total maybe of 5mm. The bolts (nice stainless button head Allen key ones) are slightly too big to go in the slider holes and are apparently metric whereas the slider is AF. So, the holes needed to be opened up by maybe 0.5mm. They were also longer than I was comfortable with, clearing the disc by a mm or so, and were therefore shortened. Still it does look real trick, with very well finished parts, and the disc hub fit is excellent.

Of course any changes from stock brakes you make, are at your own risk, and legally speaking need to be done by a qualified person and checked by an approved engineer.

Alan Lewer (galanl@actrix.gen.nz)
in the NZNOC Newsletter and June 1997 'Ocker Noccer' (New South Wales Norton Club newsletter)


Alternative master cylinders for the front disc brake

My opinion is that it's not all that important to retain the original appearance of a braking system that everyone knows is poor. From everything I've tried, it seems the pads are the weakest link in the Lockheed chain. And of course, they're so small, it's hard to do much better.

As an order of first priority, I would check into high-friction modern technology pads. As for sleeving the master cylinder, it would be fairly tricky, aside from the logistics of making up a new piston (I've made them up in the past, from stainless bar), you'll need to carefully drill tiny, tiny holes in the sleeve for the feed and bleed holes from the reservoir. These are somewhere in the size of 0.010", and not easy! Then of course, you'll need to de-burr the bore of the sleeve after drilling, or say good-bye to your new seals. The other snag to watch for is the sleeve creeping while in use. When this happens, the sleeve blocks the ports, rendering a complete loss of brakes! In my case, I couldn't get adequate performance at all with much fiddling with the Lockheed components, and finally fitted an entirely new system: why take half measures? With careful selection of components, it turned out to be fairly easy.

I used a 4 piston caliper from a 1986 Suzuki GSXR-1100, along with a 12.5" floating disk from a 1989 GSXR. A disk from the 1986 model would have been better as far as alignment, but I could not find a really good one at the time. No matter, the newer one worked well. You could opt for disks from the 750 if you did without the floating hub. As for the master cylinder, I initially used the Lockheed, which was OK, but the hydraulic brake light switch was dodgy.

Thereafter, I fitted a 5/8" bore unit from a Honda CBX. It worked very well, except the lever travel was a little short for my liking. Still later, I fitted a 13mm master cylinder from a 1982 Yamaha XV550, which is there to this day. I did not notice all that much improvement in braking over the 5/8" bore unit, but the lever travel is much more pleasant. The only downside to the conversion at first was losing the perch for my off-side rear view mirror. I later solved this by milling one from a bar of 6061-T6 alloy, and fastening it to the place where the Lockheed master cylinder used to be.

Greg Kricorissian (grkricor@ccs.carleton.ca) on NOC-L 11th. Sep 1997


Finding alternative sources for master cylinder seals

The seals on the Commando master cylinder are standard fluid seals. Indeed the seals on the fork legs, ignition rotor, crankshaft, etc., not only on Commandos but on just about any bike, built by any manufacturer, anywhere in the world, are standard fluid seals. Very rare is it, to find a bike manufacturer make up such a simple part as a one-off. Only the dust boot is in any way special, on the Commando, and even then, I think it was a common fitment on many British Leyland car master cylinders of the time, along with the wee retaining washer thingy. (Commando brake discs are identical to Ford Capri ones, I believe).

Just look in your local Yellow Pages and find a dealer who specialises in such items and quote the diameter and thickness you require. The main item you want is the correct thickness of fit, at the piston (I mean lengthways thickness, obviously). It'll help if you take the old one along, with the newly worked piston, and explain your problem.

D.J. Walker (djw12@leicester.ac.uk) on NOC-L 11th. Sep 1997


Increasing leverage by modifying the brake lever pivot

I found the squeeze on my brake much too hard and also the rest position of the lever too far away to grab with my rather small hand. Eventually I got the same effect as resleeving by relocating the pivot point of the lever to bring it nearer to the piston, thus giving more mechanical advantage. This involved plugging and redrilling the holes in the casting and the lever and was tricky, but not inordinately so. This can't give you as big an improvement as resleeving, because there's a limit how close the pivot can get before it breaks into the brake cylinder bore itself, but the improvement was very satisfactory I wrote it up in Norton News about 10 years ago, if anyone's interested.

Personally, if I were resleeving a master cylinder, I wouldn't try to turn down the piston, but instead I'd get a damaged master cylinder from a Honda or other large-production Japanese bike that already had a suitable-sized piston (and make sure to find out which year and model bike it was), then just bore a sleeve for the Lockheed out of suitable metal until the piston had the same clearance it had in its original cylinder. That way, you'd have the right clearance for the piston (or at least what the original Japanese engineers thought was right) and you could get the right replacement seals for that piston at the appropriate Japanese-bike dealer.

Mike Taglieri (miketync@aol.com) on NOC-L 13th. Sep 1997


Grimeca alternatives - a reference

As has been stated, modifying an existing handlebar master cylinder can be problematic. It has been suggested that Buna N O-rings should be the correct material for the seal, but that's a question I haven't seen a peep on.

A difficulty with some of the O-rings is they sometimes have a mould separation line on the largest part of the o.d., where you don't want it! Grimeca used to have a normal sized reservoir 14mm handlebar master as well as the small reservoir ones in 13mm and 14mm as shown on http://www.thekinetics.com/phantom/sonofP11.htm but don't go road racing with the teeny reservoir; we have had trouble with it (the kind you don't want to duplicate) as the pads wear, and with big lean angles! Even on a street bike, you do need to fill the reservoir to the top level, then angle the lever to taste and check the level once in a while. Failure to do so could be 'troublesome'.

Tom Davenport (tom@thekinetics.com) on NOC-L 13th. Sep 1997


A Kawasaki alternative master cylinder

The shop that once advertised in the Norton News discontinued modifying master cylinders do to lack of demand and profits. I have been using one of their modified master cylinders for about 3,000 miles with great results. The difference between the original and the modified cylinder is phenomenal. The lever has more travel, which is expected. This additional travel gives me more 'feel'. I can now lock up the front wheel at will and in a totally controlled fashion. Keep in mind my caliper is stock.

The modification can probably be duplicated by somebody with good machining skills. A Kawasaki EX-500 master cylinder rebuild kit is purchased. This kit includes seals and a new piston. Using measurements from the Kawasaki and stock Norton piston a special piston is machined with length and profile similar to the Norton one but with seal grooves that have the dimensions of the Kawasaki piston's seal grooves. The master cylinder is sleeved to reduce its diameter to that of a Kawasaki master cylinder. I do not know what this exact diameter is, the press fit (interference fit) of the sleeve, or how it was done. I seem to recall the owner of the shop telling me he experimented until he found a sleeve size that would yield the correct press fit and inner diameter once pressed so no additional machining was required. I am not sure if the master cylinder bore was machined prior to sleeve installation in order to allow for a sleeve with thicker walls.

Raul M. Biascoechea (raul-sandy@juno.com) on NOC-L 16th. Sep 1997


A disc brake modification using Suzuki and Yamaha parts - full instructions

I had some interest in the brake modification I did to my Mk.lll 850, so here's a quick overview of what I did. The conversion worked out quite well; taking the following steps:-

  • (1) Mount the disc rotor to Norton hub with adaptor plate
  • (2) Mount the caliper to the fork leg with adaptor plate
  • (3) Assemble caliper and rotor and shim to centralise
  • (4) Mount master cylinder; fabricate SS lines

I wish I could say that I had CAD drawings of the adaptors that I could email to you, but that is not the case. I designed them in the best traditions of cafe racers everywhere; by hand drafting the key dimensions on paper, and then developing the finished shapes on cardboard templates.

(1) The 1989 Suzuki GSXR 1100 disk has a centre hole that is a little larger i.d. than the spigot on the Norton hub, and the bolt holes are on a larger circle than the Norton disc, so the first thing you need to do is to machine an adaptor plate that sandwiches the disk rotor to the hub. This plate is made from ½" 6061 T6 alloy, machined so that the spigot is the thickness of the disk rotor hub, with the remainder left for the clamping surface for the plate. The spigot in the plate is raised in its centre in order to centralise the disk on the hub ,and locate it. The o.d. of the whole thing is the diameter of the depressed center of the rotor. Once the sandwich plate is machined; mark out, drill, and then countersink holes in the plate to match up with the original holes in the Norton hub. Lastly, drill holes in the hub of the Suzuki brake disk rotor to line up with the Norton hub. Assemble the sandwich plate and disc to the Norton hub with 5/16" UNF flat head Allen screws, torqueing them evenly.

(2) The 1986 GSXR 4-piston caliper is light, works well, and is easy to find. A similar version was also used on the Gamma 550. There is lots of choice in pads; I used ones with Kevlar linings. I mounted my GSXR 1100 caliper on an alloy plate made from 3/8" 6061 T6 sheet. The plate bolts to the outside surface on both the caliper's mounting lugs, and the two lugs on the Norton fork lugs. I considered making the plate extend downward to pick up one of the smaller lugs. Originally, the shape of the plate is designed so that it hugs the outline of the caliper, and overlaps the lugs on the forks to the greatest extent possible.

(3) Assemble the disk onto the hub if you haven't already, and install the completed wheel into the forks. If you're using the late GSXR disk, you will likely find that the grommets will lightly foul the fork slider. Fix this by installing a small distance piece on the axle between the fork leg and the bearing in the hub. Bolt the caliper plate solidly to the fork leg, and align the center line of the caliper on the rotor. Make up distance pieces to suit the required amount to space the caliper on the plate. When you're finished deburring smoothing and polishing, ensure everything is tight, and be sure to use at least Grade 5 bolts and nuts.

(4) I used a Yamaha XV550 master cylinder with a 13mm bore. It mounted very nicely inboard of the standard Norton switch gear, and looks 'right'. You may choose to retain the Lockheed master, but lever travel may be limited, and the hydraulic brake light switch is marginal at best. What ever you do, spend the money on braided stainless/teflon lines.

The final thing I did on my bike was to fabricate a right side mirror mount, since using the Yamaha master cylinder means the loss of the stock mounting boss. I machined a suitable 'L' shaped mirror mounting from a block of 1" x 1" x 2" 6061 T6 alloy, which bolts to the upper two screw holes for the original master cylinder mounting in the twist grip, and juts forward to pick up the mirror stalk, which threads (10mm x 1.0) into the alloy.

Greg Kricorissian (grkricor@ccs.carleton.ca) on NOC-L 16th. Sep 1997


Brake seal materials

While the dimensions of brake seals may be standard, the material is (should be) different for brake seals. Common nitrile will swell in time when exposed to glycol based (DOT 3.4 in the US) fluids. The recommended material for brake seals is ethylene-propylene. There is actually a specific E-P compound for this but I have good luck with the generic compound. O-rings in this material can usually be found at an industrial supplier. Other seal types may be difficult to find except from the brake manufacturer.

I have been running a Dunstall dual front brake unit since 1972 and was changing caliper O-rings every one to two years until I was informed of this fact. It has now gone for 7 years with no leaks.

Pete Serrino (serrinop@ehsct7.envmed.rochester.edu) on NOC-L 16th. Sep 1997


Improved front brake lever - a source

I have a friend that can do stoppies using the original Norton brake components and race compound rubber but he has the upper body strength of Arnold Schwarzenegger. To get the same results I need to use a rotor with the chrome plating ground off, EBC pads, braided steel line, and a Lockheed Racing brake lever from RGM Motors which has an improved ratio over the standard item (part number APCP2233).

Gary Slabaugh (gdslabaugh@sprintmail.com) on NOC-L 16th. Sep 1997


More on brake seal materials

E-P seals should be available in general sizes from good suppliers of these goods.They may be hard to source in the U.S.A., but are not in the UK.

Standard fluid seals can be used with silicone brake fluid, which anyone who lives in the late 20th century ought to be using. So, if you have difficulty, switch to silicon fluid and use standard seals.

D.J. Walker (djw12@leicester.ac.uk) on NOC-L 20th. Sep 1997


Success with the Kawasaki based conversion

I have now modified my front master cylinder along the lines suggested by the modifications to Raul's brake. The modification was cheap, easy, quick. The cylinder was sleeved to 1/2 inch and a piston made with the length dimensions from the Norton one and the width dimensions from the Kawasaki.

I can report that the front brake has been improved about 100%. It doesn't lock up the wheel above about 10 m.p.h. but it sure hauls the speed down without desperate forces on the lever. It makes me want to laugh with glee every time I put the brake on. It just stops.

Chris Ghent (ghent.chris@a2.abc.net.au) on NOC-L 8th. Oct 1997


A front disc brake conversion based on Honda parts

I have been running a beat up old master cylinder off a Honda CB450 on my 850cc Norton now for years and years. It's not too pretty, but I actually like it more than that cludgy giant integrated set up on the Mk.lll or even the standard Lockheed model. Admittedly, I am not at all concerned with maintaining a 'stock' appearance or any of that - but the real reason it's lived on my Norton for so long is that it works so very well. I can easily bring the front wheel to near stoppie (rubber 'chirping') and have excellent control - all for a total cost of about $10 or so (used - swap meet). Other factors: none, except for no chrome on the disk; otherwise stock caliper, lines and pads with the only drawback being no integrated brake light switch.

This setup has worked so well that for years now I have put off spending the approx $100 for a Grimeca or Magura, and I run the thing in the city with no back brake; I just haven't felt the need to buy that new rear master cylinder.

The bore on the Honda master cylinder is 13mm (or thereabouts) and is thus smaller: a smaller bore gives higher line pressure for less force exerted and hence better braking. My 'conversion' was this simple:-

  • (1) Take the old Lucas handlebar piece off
  • (2) Replace it with any Honda CB450 master cylinder from ca. 1974
  • (3) Since the pipe thread used is the same in the UK, USA and Japan, use whatever line is the appropriate length.
         You will have to eliminate the stock line pressure switch for the brake light as it screws directly into the Lucas
         master cylinder assembly - but it can be replaced with an in-line one (also cheaply and widely available)

Bennett (bennett30@earthlink.net) on NOC-L 30th. Oct 1997 & 13th. Nov 1997


A disc brake modification using Kawasaki parts - full instructions

Some time ago I started a thread on the list to do with Commando front brakes and subsequently modified mine along the lines suggested by return letters. I acknowledged the success of the project but wondered whether anybody would be interested in the full story.

My brakes have been through a few permutations. There was a time when they were just inadequate; that was when you could push the bike forward with the brake hard on. This was followed by the period when the fork seal was leaking all over the pads. Things improved when I rebuilt the master cylinder and bought a new and shorter brake hose. The brake was a lot better, but still the fastest the bike had ever pulled up was when I was bringing it home on the trailer.

A few months ago I ground 3mm off the actuating end of the lever to bring the lever in closer to the grip. I tapped a small screw into the back of it to adjust free play and this meant I always had a handful of lever in an emergency rather than the tips of my fingers clinging on in desperation. Somewhere in my trawling through magazines I had come across the notion that the smaller the master cylinder piston in relation to the caliper pistons, the more force could be exerted on the pads. Applying this small bit of knowledge to the Norton brake meant that if the piston were smaller, while it would have to move further to have the same effect: it could place more force on the caliper at the same lever pressure, and maybe produce more braking effect.

I decided to sleeve a Lockheed down and see if it would stop the plot. The very next day in the next bunch of NOC-L messages, a bloke called Raul who works in Seattle registered that he had had his cylinder sleeved, taking the bore size from 5/8" to 1/2", using seals off a Kawasaki EX 500 (GPZ 500 in Australia). He made the piston by taking relevant measurements from the Norton and the Kawasaki pistons.

I took the cylinder to Marion Brakes where a bloke called Terry Milligan gave me lots of info and sleeved the cylinder to 1/2" in stainless for A$47-00. I bought a seal kit for the Kawasaki for A$49-00 , and to provide more information, bought a second hand complete cylinder from a wrecker at a cost of A$50. There are twin and single disc EX500s and this modification needs the single disc kit. I spent some time looking at the two pistons, the Lockheed and the Kawasaki: they were just so different. In principle I had to take the diameter measurements off the Kawasaki and the lengths off the Norton, but there were complications.

I had to build in the groove for the boot, that was easy; but the primary seal, that's the one that does all the work, is a free floating full cup that sits in front of the piston on the Norton. On the Kawasaki this is a ring cup like the Norton secondary seal. Would this matter? Also, between the primary and secondary seal on the Kawasaki there was a spiral groove. Was this a piece of job justification from a Japanese designer and if not, what did it do? Additionally, at the end of the Norton cylinder is a rubber valve that restricts the flow; the Kawasaki doesn't have it. What was it supposed to do?

In a flash one night I realised the spiral groove was actually a bearing surface, grooved to allow the fluid to pass through. The bearing was necessary as the flange in front of it supporting the primary seal which you would expect to be the bearing surface had to be able to allow fluid to pass over it and past the seal on the exhaust stroke, and consequently could not be a close fit on the cylinder wall. Another worry was whether there would be enough distance between the two ports in the bottom of the cylinder reservoir to allow the increased travel needed so the smaller piston could still pump the same amount of fluid. A reduction of 5/8" to 1/2" is 50% less in terms of area. The answer meant the piston would have to travel half as far again as it used to.

I measured the travel in a standard setup; it was about 9mm - the new setup would therefore need about 14mm. Comparing the distance between the seals on the Norton piston and the positions of the holes in the reservoir showed there was about 20mm available. In action, the primary cup has to start close behind the primary port, which is small so it doesn't rip the cup as it passes over it. The hole is there so the fluid in the line and caliper is the same body of fluid as in the reservoir. As soon as you move the lever, the primary seal moves across the hole, closes the system, and then begins to pump fluid down the line. The secondary seal travels behind it and basically scavenges the system, pumping excess fluid back into the reservoir through the secondary and bigger port. The brake must take up before the secondary seal reaches this port. In the modified brake there is plenty of room but the secondary port could be shifted closer to the primary port if you wanted to use another caliper such as one of the fancy Lockheed ones which probably need more fluid to be pumped than the original. This would only work as long as the primary cup does not reach a travel limit in the bore, such as the compressed spring, before it has pumped enough fluid to put the brakes on. If anyone ever gets that far please take into account the wear on the pads. Failure to do so could result in an event to be filed under the category sudden frightening experiences at speed with crosslinks to stain removal and the parts list.

I produced a drawing of the piston which was duly translated into metal. I was thrilled when the machinist cut it off the lathe and handed it to me. I hurried off home, fitted the seals and installed it on the bike. The first thing I did was put as much pressure on it as I could, both hands at once in a primitive pressure test. I then pushed it forward and the instant I touched the brake it stopped dead. There was nothing more I could do without taking it out. I progressed down the street trying it harder and harder. Satisfied it wasn't about to pop, I rode to a clear area and whacked it on hard. The effect was so dramatic I found myself laughing. I rode up and down crashing to halt and soon my wrists were aching from the effort of holding on.

I found I could make the wheel chirp from about 20 m.p.h. down and occasionally it could be locked up if I tried hard. The increased lever travel means more feel, so its great on the open road. I used the spring from the Kawasaki kit; it was a little short so I stretched it from 40mm to 55mm. I have now decided it is not strong enough and intend to wind my own sometime. Without complete confidence in the decision, I left out the flow reduction valve in the end of the bore. This part probably generated more talk than any other aspect of the conversion. I decided it was either a slow on/fast off valve with a roll in a prevention of front end dive or lockup, or it was a relic of attitudes towards brakes at the time of the original design.

I rang Brian Slark who was rumoured to have made this modification at some stage. When I spoke to him in Alabama he was welcoming and encouraging but had no info. What he did have was insight into the original process of designing the brake. "We tried to make it as much like a drum brake as possible" he said, citing consumer resistance to new technology as the reason. He also said they were worried about young American kids hauling the thing on, losing the front and then sueing Norton. In order to satisfy these worries they cleverly made the brake so it didn't work. It was clearly enough in the eyes of the sales people to be seen to have a disc. Its a great feeling twenty five years later to experience the brake the Commando could have had, and from the outside no-one can tell the difference. It's now been on the bike for a couple of months, which translates into about 1200 miles.


So what did it cost? In total about A$220 of which about A$100 was development costs. Anyone following needs to sleeve their cylinder at a cost of $47-00, buy the seal kit for A$49-00, and get a piston made for what? - my guess is about A$30 to A$40. I now have the piston design as a .BMP file if any one wants to clap eyes on it. Mine is made from aluminium bronze 2, and the cylinder liner is stainless steel, although other materials could be used.

Chris Ghent (ghent.chris@a2.abc.net.au) on NOC-L 25th. Dec 1997
and in the 'Ocker Noccer' (New South Wales Norton Club newsletter)


A Bonneville master cylinder works well

I run a Mk.lll, fitted with a Norvil 12" front disc and Grimeca caliper. On the advice of a Triumph-fan friend, I fitted a stainless Bonnie master cylinder, and greatly improved things.

Frank Westworth (classbikes@aol.com) on NOC-L 7th. Jan 1998


Experiences using a 13mm Grimeca master cylinder

I used a 13mm piston Grimeca handlebar master cylinder on a 1972 Combat Wombat about 20 years ago, and having tried many, cannot think of a nicer unit for your bike: this was with a standard issue rotor, but drilled with ½" holes (really!) and standard caliper.

The only problem I ran into, and it was a serious one, was that the caliper side fork slider wore out. A sturdy fork brace is mandatory if the slider is to have a decent life span. The extended bushing housing/seal housing (Hyde, I believe) is a terrific move toward correcting this situation by moving the top and bottom bushes further apart, giving more effective engaged support.

A possible hair-raiser is the small reservoir capacity of the rectangular reservoir Grimeca handlebar master cylinder, which really benefits from filling while level and closing up before mounting to the handlebar. Whilst I never had any occasion to be scared witless by losing the front brake due to fluid drop compensating for pad wear on the front, it could catch up those who don't check the level once in a while or use one of these on a racer or other bike with soft, rapidly wearing pads.

Nowadays, I have one of them on my P11 (10" twin disc Brembo front brakes from a Ducati 500 vertical twin and Marzocchi front end) and am delighted with it. I hope I can find another one for my next Commando! Personally, I do not care for the Lockheed-Triumph handlebar master, but without specific criticism other than it does have less line pressure than the 13mm Grimeca.

Tom Davenport (tom@thekinetics.com) on NOC-L 8th. Jan 1998


Copper plating of front discs

On my old Mk.lll, the rear disc worked better than the front, so I had the front disc dechromed, drilled and chamfered, and then copper plated (one of the initial processes prior to chroming). The copper helped to dissipate heat a bit better and gave a very satisfactorily rough surface for the pads to grab. As a result, the front disc worked almost too well.

John Kula (johnkula@islandnet.com) on NOC-L 28th. Jan 1998


Stainless steel vs. rubber brake lines

After replacing stock rubber lines with Teflon or Kevlar stainless steel covered lines about a half dozen times now, I can say it has never improved subjective 'performance' -- at least measurably. However, these replacements have improved 'feel'. The (rather expensive) change has usually made the brakes feel less 'rubbery'. One disadvantage to stainless steel covered lines -- at least if they're not covered -- stainless steel braids make excellent hacksaws. Be sure the line is not rubbing any parts which might suffer from abrasion.

John S. Morris (jsm@mediaone.net) on NOC-L 1st. Feb 1998


Chamfering holes in disc brakes

Originally, when disc brake technology was new, it was believed that drilling holes in the disc would reduce the tendency for 'solid' disc brakes to lose their grip in the wet. They were drilled, I believe, to allow water or debris a place to escape pad pressure, although it seems to me that centrifugal force should merely have slung water, mud, and debris onto the riders pants.

Modern high performance bikes drill their large diameter discs to reduce unsprung weight. My Ford pickup has no holes in its discs and they perform well, wet or dry, and the pads last forever.

In my opinion, the holes are chamfered to reduce the possibility of the drillings becoming stress-raisers. Any hole drilled in highly stressed metal will eventually cause that piece to fail unless stress is relieved. This is best achieved by avoiding any sharp edges or square sides and chamfering is a common cure for this.

Imagine, if you will, the consequences of these holes being linked by stress cracks. Home mechanics and rookie-racers are best advised to not drill parts willy-nilly in order to reduce their weight or to 'improve' their functionality, without chamfering. Brake discs, in particular, due to their cycling of temperatures can be susceptible to this failure.

Joe Michaud (triumph@fda.net) on NOC-L 1st. Feb 1998


Disc pad materials

I deal with Ferodo directly for the pads I use for race and road use for (classic) Triumph and the 2 piston AP race caliper. I am often asked for pads for the Norton road caliper, and I can say that Ferodo no longer make this pad. So, any Ferodo you are supplied will be quite old stock, not that that is any sort of problem (apart from re-supply of course).

The pad marketed as AP, in the yellow blister packs, is made under licence by SBS (Scandinavian Brake Systems?) and is in all respects apart from the number, identical to the SBS part. All newly made brake pad materials have to be asbestos free, and some of the manufacturers have been much better at developing new compounds than others. I feel there is a lot of hype and marketing involved in the sale of brake pads and that an owner may have to try several types before he discovers on that suits his riding. By the time he purchases next the compound may have been changed! However, before searching for brake performance answers in pad materials I feel it is worth remembering that fresh master cylinder and caliper rubbers, with of course new fluid, will have a remarkable effect on the feel of any brake.

Philip M. Pick (pmpick@triples.demon.co.uk) on NOC-L 1st. Feb 1998


How not to chamfer holes in discs

As others have mentioned, the holes should be chamfered - but make sure the chamfer is small. Another way to achieve the desired results (as opposed to using a counter-sink) is to place a ball bearing somewhat larger than the diameter of the hole on top of the hole and give it a good whack with a hammer.

If you do this, the metal lifts in a sort of crater around the hole. This makes an interesting noise when the brake is applied. Equally interesting is the reduced braking effect and the rapid wear of the pads...

Frank Westworth (classbikes@aol.com) on NOC-L 4th. Feb 1998


Experience with Grimeca conversion

When I acquired my Commando 850 Mk. 11a in April 1997, I was shocked to find out just how bad the front brake was. Last winter the front end was dismantled and when reassembled boasted an RGM 12 inch floating disc, a Lockheed racing caliper, new master cylinder internals, a Goodridge line, a Lockheed racing brake lever, and a new Roadrunner (100/90 sitting on an 18" WM3 Akront).

I took it out down the road, gently squeezed the front brake lever and - nothing; squeezed a bit harder and - nothing, so grabbed it as hard as I could and was aware of the faintest sensation that the bike was very gradually losing speed. I was so disappointed. Even though I tried EBC green pads, and overall braking was better, it was not what I had been expecting.

There does appear to be a wide discrepancy in the performance of standard master cylinders. Although always lacking in feel, some standard set-ups are capable of locking the front wheel; mine was not. I read with considerable interest Nick Forster's article in Roadholder 196. I then met him at the BMF and after discussing the merits of the Grimeca 13mm master cylinder I ordered one from RGM. The result is more or less as Nick described in his article. It is two fingers powerful, controllable and it is the difference between a machine which is downright dangerous on public roads to one which inspires confidence in all road and traffic conditions. In fact I was temporarily satisfied.

On the downside I'm not over impressed with the build quality, and I'm having problems with the odd weep of brake fluid despite using new copper washers; but the improvement for around £45 is incredible.

Adrian Draper (adriandraper@adelanta.co.uk) to Editor 16th. Sep 1998


 

[There is more about disc brake modifications for Commandos on the Members Only pages, from the Norton Owners Club magazine Roadholder, issue No. 196 - Editor]

 

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