Norton P11 Disc Brake Front Option

mdt-son said:

I am surprised you guys don't have much respect for type approval and structural safety issues. The P11 was never factory approved for a disc brake.
In theory .... a disc brake can NOT be fitted to any drum brake bike, unless it has been proven to withstand the braking loads and without causing judder, fork twist and binding of the headstock races, etc.
Obviously you have never welded aluminum, and even less an alloy fork slider. I have (even an AMC one) and I can testify they will distort and ovalize. This is not a viable path. Better to have one slider machined from billet. It's not going to be cheap. Our esteemed member Madass gave up producing his sliders because of machining difficulties.
I do not know how your metal slippers are intended to work, but ... a drum brake can be set up to work really well.
-Knut

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Re; “Obviously you have never welded aluminum, and even less an alloy fork slider”

Yes I have, but with a mig welder ,- my welding is in all honestly not very good 75% of the time; I did say get it TIG welded by someone who does alloy welding all the time.

Re; “I do not know how your metal slippers are intended to work,”

Its an old solution- as old as the hills, Read the posts on the Other Nortons and Commando blogs , at one time you could buy these from my local motorcycle emporium, now I just make my own but ideally they should be hardened and tempered.

If you really want stopping power, Molnar Precision Ltd. will sell you a Fontana 210mm 4LS or a Ceriani 230mm 4LS hub, When polished, these would be far less obtrusive visually than a disc brake.
New sliders should be used, as the old oem sliders are porous and there are reports of sliders cracking when subjected to hard braking.

For the inventive souls, a 2LS brake plate fitting the intermediate hub shouldn't be difficult to make (the brake plate would have to be turned out of a billet disc).
At one time AMC may have experimented with a TLS conversion for racing G12's according to a member of the AJS/M club ......

Of course the 7R/G50/E95 8in 2Ls front hub may be fitted also ....

-Knut

Please find a tasty one-off TLS conversion of the 1955-62 hub and brake plate below. A similar conversion can be made for the 1963 type of hub and brake plate (as used on the P11).

- Knut

The late 60s BSA /Triumph 2 LS is a powerful brake. Im not sure as to what would be involved in fitting it to a Teledraulic fork.
I fitted one to an A 10 Super Rocket and that definitely solved the weak brake problem.
Now I have to do something about the front forks bottoming every time I pull the brake on with gusto.

Glen

I have converted quite a few drum braked bikes to disc, as although it might not look original, it certainly won't when you've run into the back of another vehicle. I have just finished putting a Brembo caliper & Honda CBR 1000 disc on my A65, but would most definately not fit a really powerful brake to original old Teledraulics. The stanchions are only 1.250" diameter & the sliders are very thin & not particularly strong. I've seen a few cracked ones over the years.

Martyn.

Matchless said:

I have converted quite a few drum braked bikes to disc, as although it might not look original, it certainly won't when you've run into the back of another vehicle. I have just finished putting a Brembo caliper & Honda CBR 1000 disc on my A65, but would most definately not fit a really powerful brake to original old Teledraulics. The stanchions are only 1.250" diameter & the sliders are very thin & not particularly strong. I've seen a few cracked ones over the years.

Martyn.

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Cracked from sheer braking force? Or just cracked?

I don't know, but a G9 I bought to restore in the nineties came with a cracked slider. As it was beyond safe repair I cut it in half to see how thick the material was, & was suprised by just how thin a section it was. It also I remember, seemed rather brittle. There is a company in England making new replicas, but just how good/strong they are I have no idea.

p400 said:

The more miles I put on this P11, the more disappointed I am with the front brake.

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Old thread I know

Getting comfortable with how quick one can ride a P11 in the twisties will bring out the worst in that front 7" SLS brake. They were not intended for road racing and doing things like entering downhill turns at any significant speed. People say drum brakes don't fade, but they must ride too slow to know any better.

As mentioned, a drum can be made to stop as well as a disc for street use. The caveat is weight. A really good stopper drum is going to be heavier than a dual disc no matter how you look at it. Plus they are expensive. Ridiculously so. Only reason front drums are still around is historic racing and the restoration market. Sure as heck isn't because they work better than a disc brake.

mtd-son brought up the point that P11 frames were never approved for disc brakes. Personally, I doubt they were ever tested for disc brakes. Off road bikes did not have disc brakes in 1967. I don't think many bikes of any flavor sold new at that time did. The point about the head bearings not being real happy with more brake is a good one though. Too bad nobody makes a drop in bearing kit for that old P11 frame. This is the part where somebody better with google than I provides a link to a head bearing set that drops into a P11 frame. I can dream can't I?

Schwany said:

Old thread I know

Getting comfortable with how quick one can ride a P11 in the twisties will bring out the worst in that front 7" SLS brake. They were not intended for road racing and doing things like entering downhill turns at any significant speed. People say drum brakes don't fade, but they must ride too slow to know any better.

As mentioned, a drum can be made to stop as well as a disc for street use. The caveat is weight. A really good stopper drum is going to be heavier than a dual disc no matter how you look at it. Plus they are expensive. Ridiculously so. Only reason front drums are still around is historic racing and the restoration market. Sure as heck isn't because they work better than a disc brake.

mtd-son brought up the point that P11 frames were never approved for disc brakes. Personally, I doubt they were ever tested for disc brakes. Off road bikes did not have disc brakes in 1967. I don't think many bikes of any flavor sold new at that time did. The point about the head bearings not being real happy with more brake is a good one though. Too bad nobody makes a drop in bearing kit for that old P11 frame. This is the part where somebody better with google than I provides a link to a head bearing set that drops into a P11 frame. I can dream can't I?

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I made my own. It wasn't hard. They are a tight fit into the steering head (had to use a brass hammer to tap them in), and I am using tapered roller bearings in them. The down side is that the resulting steering head assembly is a good inch taller than it was with the loose ball bearings, which limits the number of front ends you can use due to the length of the steering stem. But it can be done. I'm running a Kawasaki KZ1000P front end on mine with an early 1970's Honda CB front hub and disc laced into an Akront style flanged rim. Haven't decided what caliper I am going to use yet, but I plan to use something from the 1970's. I've considered a vintage aftermarket Lockheed, but even the repops of those are pricey. I may go with an early Gold Wing caliper, which can be made to look vaguely Lockheed-ish. Or I may go with an early KZ caliper, which might bolt on to my front end, I haven't checked yet. But yeah, I agree with you on the disc-drum thing. In my experience, having ridden a lot of bikes with both, I'll take the front disc every time. I care less about the rear brake, though again experience has taught me that a good rear brake will make it possible to ride quite a bit faster in the twisties than a lousy brake will. Better braking, better feel, less maintenance, what's not to like? Okay, it's not OEM, and that is kind of a shame, but on the other hand, do you own it to ride it or just to look at it?

baz said:

Cracked from sheer braking force? Or just cracked?

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I think I read these were prone to cracking if moisture was allowed to build up, as their 'flimsy' construction made them prey to frost damage if the oil wasn't changed regularly..

EstuaryBoy said:

I think I read these were prone to cracking if moisture was allowed to build up, as their 'flimsy' construction made them prey to frost damage if the oil wasn't changed regularly..

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I've seen project commandos for sale with cracked sliders from standing outside in the winter

Junglebiker said:

I made my own. It wasn't hard. They are a tight fit into the steering head (had to use a brass hammer to tap them in), and I am using tapered roller bearings in them. The down side is that the resulting steering head assembly is a good inch taller than it was with the loose ball bearings, which limits the number of front ends you can use due to the length of the steering stem. But it can be done. I'm running a Kawasaki KZ1000P front end on mine with an early 1970's Honda CB front hub and disc laced into an Akront style flanged rim. Haven't decided what caliper I am going to use yet, but I plan to use something from the 1970's. I've considered a vintage aftermarket Lockheed, but even the repops of those are pricey. I may go with an early Gold Wing caliper, which can be made to look vaguely Lockheed-ish. Or I may go with an early KZ caliper, which might bolt on to my front end, I haven't checked yet. But yeah, I agree with you on the disc-drum thing. In my experience, having ridden a lot of bikes with both, I'll take the front disc every time. I care less about the rear brake, though again experience has taught me that a good rear brake will make it possible to ride quite a bit faster in the twisties than a lousy brake will. Better braking, better feel, less maintenance, what's not to like? Okay, it's not OEM, and that is kind of a shame, but on the other hand, do you own it to ride it or just to look at it?

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You chose the right way to go for a retro modified street bike as far as I am concerned. I went nostalgia on the front brake replacement for my version of P11. The big drum nostalgia bit me in the arse due to a quality control issue. I would not fit one again on a bike that will only see the street regardless of where I can get one because of the weight and maintenance issues.

Made your own head bearing set?
Did you write that up anywhere?

What did you start with and how did you modify the bearings and head set. I have longer forks than stock already on the old P11. I could easily work with the longer head and stem height required.

Schwany said:

You chose the right way to go for a retro modified street bike as far as I am concerned. I went nostalgia on the front brake replacement for my version of P11. The big drum nostalgia bit me in the arse due to a quality control issue. I would not fit one again on a bike that will only see the street regardless of where I can get one because of the weight and maintenance issues.

Made your own head bearing set?
Did you write that up anywhere?

What did you start with and how did you modify the bearings and head set. I have longer forks than stock already on the old P11. I could easily work with the longer head and stem height required.

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Eventually I'll have to figure out how to post pics to the site--I did take some, though they may not be super quality. To make my bearing adapters, I started with a coupel of chunks of mild steel round stock a little more than 2.75" in diameter and about 3" long. The surface of these chunks of steel was heavily pitted, it'd been sitting outside somewhere for many years, I guess. Anyway, once I had a nice, uniform surface, I turned one end down so that it had a shank about 1" long that fit tightly down into the steering head. The other end I turned down to where it matched the outside diameter of the steering head. Through the middle I drilled a hole a little bigger around than 1", big enough for the steering stem to fit through with plenty of space, but not so big as to make the wall thickness any less than about a hundred thousandths where it fit into the steering head. On the lager diameter end, I machined a seat for the outer race of a set of bearings intended for a Kawasaki police bike. The lower bearing is larger than the upper bearing and so I had to make the seats different sizes accordingly. I also designed it all so that the new seals that came with the bearings would have a place to seal. I am pretty pleased with the final result, and I promise to get pics up as soon as I can figure out how.

Junglebiker

A couple of points. The headstock casting is rough inside and will not provide a good support for loose bearing adapters. At the very least the headstock needs to be line bored. A shank of 1" only is pretty short. These adapters should be much longer, bridging the gap formed by the spine tubing aperture. They should be braced in place. Additionally, the centerline of the casting may not coincide with the centerline of the bearing seats machined by the factory. Line boring need to take this into account.

My largest concern about this mod is frame strength. Please recollect where this frame came from. Developed for the G85CS as a Rickman 650cc contender, bending stiffness of spine and downtubes are marginal. No need to consider hard braking for a track bike! The P11 on the other hand .... in the guise of a street scrambler it had deserved a different frame. By keeping the same front brake the G85CS had, NV may have argued the frame stress criterion was fulfilled .... I doubt NV ever performed a re-analysis of the frame.
Yes, they did fatigue testing as seen in the 1968 Commando widow frame testing video we all have seen.

You are fitting stiffer forks and a much more powerful front brake to a frame for which it was not designed, without strengthening the frame. This is frightening! Are you willing to take the chance of a frame breakage? Or ruptured joints? Without a proper stress and strength analysis and/or testing, your approach is irresponsible IMHO.

If the frame and it's original brake doesn't suit your riding style, the obvious solution is to look for a different bike or at least a different chassis.

Some keywords: Metisse, Wasp, Ase Custom, Dresda, Metal Malarkey Engineering. D&M Engineering, Framecrafters

My 10c.

- Knut

Knut! I was expecting something like this from you. Thanks!

Would it be viable to laser weld caliper mounts without distorting the lower fork leg?
I do know a local who modified a number of Commando fork legs this way to take a Japanese caliper. The only details I recall was that the person who did it had access to sophisticated welding equipment through his employment.

nortonmews said:

Would it be viable to laser weld caliper mounts without distorting the lower fork leg?
I do know a local who modified a number of Commando fork legs this way to take a Japanese caliper. The only details I recall was that the person who did it had access to sophisticated welding equipment through his employment.

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Unlikely, but why don't you ask your acquaintant? By using telescopic gauges, it's easy to find out if and by how much a "tube" deforms. Yes, essentially the slider is a thin-walled tube, and even if laser welding is a process which develops localized heat, it is not a cold process. Any heat impact will release residual stresses from the casting process, resulting in ovalization of the "tube". Thus, you will be better off by not applying heat directly onto the slider.

Why do we discuss welding? There are lots of sliders which can be adopted to the "Teledraulic" stanchions. You will need to machine two pairs of wider bushes only. Converting the damper and spring system requires more ingenuity, but I am sure it can be done.
Alternatively, it's not rocket science to order a set of triple trees (crown and yoke to you brits) which mimics the P11 triple tree. Note: I believe there is an "ANG" involved for adjustment of the trail.

- Knut

People have been modifying motorcycles for years without laboratory test facilities and factory approvals. NV back yard parking lot and road testing was not sophisticated. Actually, ridiculous by today's standards. I believe the P11 can benefit from more front brake and the frame survive it. Anyone that doesn't believe that should definitely play it safe and stick with the little 7-inch SLS brake and be happy with it.

Schwany said:

People have been modifying motorcycles for years without laboratory test facilities and factory approvals. NV back yard parking lot and road testing was not sophisticated. Actually, ridiculous by today's standards. I believe the P11 can benefit from more front brake and the frame survive it. Anyone that doesn't believe that should definitely play it safe and stick with the little 7-inch SLS brake and be happy with it.

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The key word is "belief".

As for testing facilities with NV (Plumstead actually), we know precious little about them. One thing we do know is, they employed very experienced test riders who clocked up thousands of miles on new models and provided reports in writing. Dirt bikes and road race bikes were tested to the ground. It took AMC two years to develop the G85CS. I wouldn't call the test regime ridiculous. Except for abundance of electronic sensors and telemetry found in testing vehicles nowadays, practical testing is conducted much the same way today, probably on a smaller scale though because component testing and design simulation is so elaborate.

- Knut

One thing to remember here is it doesn't really count how powerful a disc brake is or a drum brake is
The tyre will break adhesion at the same point
IE if that SLS 7" could lock the front wheel up at any speed and skid (ok I know it's not a good example) then a bigger drum brake would lock up at the same point
So would a single disc
And a dual disc
Usually there is a fair safety margin built into something like a motorcycle frame should be able to take a pounding although the widowmaker commando did not!!!
I'd guess a more powerful brake would be fine if used sensibly
No stoppies etc
And braking hard from a 3 figure speed on a regular basis