'70 cmdo drum brake question

never been happy with the brakes on my bike (well, one of my other bikes is a 2010 bmw r1200r).

i don''t know if they are as good as they can be or not.

so i'm guessing one way to find out is ask if anybody knows if any of the cycle mags ever published a 60mph to zero stopping distance. or maybe somebody here knows how many feet it should stop in from 60 mph.

i haven't measuered this with my bike but will do so soon.

found this,
http://www.oldbritts.com/14_063410.html
and this,
http://www.britbike.com/forums/ubbthrea ... ber=320731

thanks,
ed

Ya gotta be kinda honest with yourself and ask how much do I value authenticity and how much do I drive the 70 enough to upgrade to disc for it if you be a driver and NEED to stop but good n' fast. Mine worked well for the first years then the wet factor caused delayed-stoppage alarm in head to fit a later disc type. The drum is one good look'in brake though. My regular ride be a B.ig M.oney W.asted R1100 RT so as you state there is NO comparison and the A.B.S. system only kicked in once for a second. Our 70's are now about 43 years old ,so they are what they are.

I thought we'd been through this. My front brakes used to be about as good as throwing out my feet, I had to plan 3 miles in advance of where I was going to stop. But believe me, these brakes can be made to work adequately. You need to arc the shoes to the drums with #60 sandpaper glued into the drum so you have at least 90% contact. Then you need to set up both shoes so they contact at the same time and the shoes are centered in the drum. It takes a bit of setup, but in an afternoon it can be done. Now my TLS will drag me down from 60 just fine, couldn't compare it to the Mini my wife has, but it's perfectly adequate unless you're racing because it will fade big time. It just depends on how good you want it. Get the high friction shoes from RGM and do the work. I'm happy with mine, and it's 90% better than it used to be. PM me if you want details. Or there have been a few threads on it here in the past.

The other option is send them out to Vintage Brakes for $$$. It's not magic.

Dave
69S

There was an article about the drum brake in Classic Bike Guide earlier this year. Ex-factory engineer Brian Dolman said he was asked to investigate complaints about poor performance at the time; he found that the linings weren't rivetted properly, allowing a 15 thou gap in the middle, plus poor machining. Once sorted he got a 1.5G force on braking. Braking distance was measured by firing a chalk cartridge downwards when first operated.
He later developed the annular discharge silencers and got a 2-3 HP increase by fitting the exhaust balance tube lower down than the production bikes. Said the factory wasn't interested due to financial constraints near the end.

Apart from the brake drum being round and the shoes lined with good friction material the most dramatic improvement is the stiffening kit 06-3410, see http://www.andover-norton.co.uk/Stiffening%20Kit.pdf (by the way, this is a leaflet that a non-Andover Norton dealer offers in e-bay for several Pounds Sterling....).
My customers tell me the kit has improved their drum brake by an estimated 100%. I couldn't tell you any different, both my drum brake Commandos have it.
Joe/Andover Norton

I had a pre Commando 750 Atlas fitted with a Tickle 2ls front brake, which I had oversize green racing linings fitted, by a brake expert. This was then skimmed down to fit the brake drum on a mandrel in a lathe with .020 thou shims fitted (which were then removed) to the EXACT size diameter of the drake drum.
The result was a front brake suitable for racing, but beware, the brake “bites” when the green linings are cold.

For more braking power I use 1 (one!) racing and one standard lining on my shortstroke everyday Roadster. On my way to work I go through a street with supermarkets, and the good housewife in her ABS braked car tends to slam on the brakes when she sees a parking space without prior warning! Both linings in racing quality tend to be too aggressive and just lock the brake.

On my shortstroke Manx I have the '62 double duplex front brake with racing linings. Not a problem on the track at all, but stay away from it at low speeds- it just locks up solid. I fell of in the paddock once, at low speed... very embarrassing! Not a solution for a road bike you want to stop at low, sometimes walking speeds in normal traffic.

i recently got a huge increase in braking power just by changing the cable. I had done all the adjustments and the brake was still horrible. I figured out that after a certain point in brake lever travel, the cable wasnt moving the lever on the drum any farther. What was happening is the sheath of the cable was actually compressing, causing you to only be able to apply the amount of force up to whatever force it took to compress the sheath. Anyway a heavy duty Venhill gave me a giant increase in braking power

so, what's an acceptable stopping distance from 60 mph?

At N-V, I did some tests on the original front brake because of its poor performance. The first thing I found was that increased force on the brake lever beyond a certain point didn't increase braking effort. In fact you could pull the lever all the way to touching the throttle twist-grip after the shoes were in contact with the drum, even while the bike was stationary.

I then did an investigation using"brittle lacquer". This is a clear-tinted paint that, once it dries, it will crack and flake off where there is any distortion. This showed very clearly that the backplate wasn't stiff enough to take the forces applied to the pivot points for the brake cams.

I did this experiment in the last couple of weeks at N-V before I emigrated, so I never saw the follow-up, but I think the Norton stiffener kit resulted from my tests. There was a lot of work being done on disk brakes at the time, but none of the concepts had worked out by the time I left. They were all fixed caliper/sliding disk ideas which always jammed and distorted the disk

RGM Linings.
Stiffening Kit.
Arc the shoes to drum as described above.
Chamfer the edges.
Replace the cable with the stoutest you can find.
It can be made a very good brake, but will still fade if used in real anger.
This means real money, but so does a disc, and for me anyway, it stops as well as my disc braked bikes.


Classic Bike Oct. 2009, tested a 1971 750 against a 1975 850. Stopping distance from 70mph was 140m for the 750, and 163m for the MkIII. My guess is that the 750 drum as tested had not been fully upgraded/modified.

A good rule for old bikes is to always plan your stops - even the panic ones!

When one thinks about the braking technology back then, one has to remember that those brakes were typically better than the traction available from those skinny tires.

40 years ago, cars didn't stop any better than Commandos. The problem is riding a machine like this in modern traffic, where the majority of new cars have grippy low-profile radials, 4-wheel disc brakes and ABS (and a driver busy texting behind the wheel).

goo said:

never been happy with the brakes on my bike (well, one of my other bikes is a 2010 bmw r1200r).

i don''t know if they are as good as they can be or not.

so i'm guessing one way to find out is ask if anybody knows if any of the cycle mags ever published a 60mph to zero stopping distance. or maybe somebody here knows how many feet it should stop in from 60 mph.

i haven't measuered this with my bike but will do so soon.

found this,
http://www.oldbritts.com/14_063410.html
and this,
http://www.britbike.com/forums/ubbthrea ... ber=320731

thanks,
ed

Click to expand...

Not 1970, but the disc equipped '73 Commando was second only to the Sportster and Water Buffalo in poor braking :lol:

thanks..seems to me its a lot of work to downshift while braking with the '70 norton but it can help. i wonder if they did that during the tests.

anyway, i now have a reference distance (165')... thanks again


fwiw... the 60-0 distance for my bmw r1200r is 119'...

i guess i'm spoiled

Plan your panics ahead of time is great advice! Looked in to see if any drum advice might appeal to my bud Wes on his '71. I'm must be off my rocker but the best stopping cycle i've ever experienced braked so sharply I could not stay in seat nor prevent flying over handle bars w/o letting up some. All others I've tried stoppie'd before pulling down as hard and short as I got spoiled on. Definitely in my plans for a 100>0 shoot out with ABS bikes. The issue i've 'run' into on drum front is how hard it is to squeeze lever for such little effect then suddenly locking to squeal front out from under. The dang inline cable brake light switch seems to take up most the lever force before shoes engaged. Has anyone found a work around for the front drum light switch?

hobot said:

Has anyone found a work around for the front drum light switch?

Click to expand...

There's a thread about a mechanical switch tied to the lever arm on the brake - similar to the old Triumph rear brake switch. Not connected to the cable in any way

BTW, 2006 Triumph Speed Triple - 60-0 in 104.75' The S3 does have fantastic brakes, and I can't just jump from one of the Nortons to the Triumph without a little break-in time (Note to self: 1 finger on the brake lever, shift on the left, one down-five up, hold in the clutch and press the red button to start)

broken link removed

I've been thinking about putting a micro-switch on the lever where the cable comes out at the wheel and running the wires up to the connectors by the headlamp to get rid of that rubberized switch. I'm sure that would do a lot for that brake. Others have just gotten rid of the switch and make sure to use the rear brake too. I'd rather have it work right, it's dangerous enough out there.

Dave
69S

DogT said:

I've been thinking about putting a micro-switch on the lever where the cable comes out at the wheel and running the wires up to the connectors by the headlamp to get rid of that rubberized switch. I'm sure that would do a lot for that brake. Others have just gotten rid of the switch and make sure to use the rear brake too. I'd rather have it work right, it's dangerous enough out there.

Dave
69S

Click to expand...

+1

Wes used wooden clothes pins and fork/spoon cut bent to make a fail safe switch that mounts on lever and perch. Surely a small switch and tidy bracket + activating tab could be fabbed up nicer than hillbilly method though not any better function. Depending on Norton rear brake switch over front is about the scariest funniest advice I've read yet. Mine wear or get wiped out regularly so gave up on rear switch years ago.

I am so pleased to hear how dangerous to jump from sluggish Commando braking to modern jerk down bikes, as I've *exactly the opposite fear* jumping from my Peel with slight modified factory lockheed system to a modern dual super dupper dual brakes, as the modern is extremely dangerous to ride if going by the G force reflex I got on Peel just commuting slowing for blinds no panic at all or even real need to brake. Can ya even believe my sanity to state I also think moderns are braking cripples as bad as corner cripples compared to Peel on 110 front tire. Center of Gravity makes a big difference in tolerating slowing G vs just flipping on nose like a greble in a ball, ugh. I fear for those on lessor craft new or vintage.