Rear hub drum to disc conversion

For me, the motivation to loose the rear drum setup is a functional cush drive and loosing a lot of unsprung weight. And a predictable rear brake for wet weather braking is always nice.

ludwig said:

montelatici said:

Why would you replace a rear drum brake with a disc brake? That's some more hydraulics to go bad in time. Do you actually use the rear brake outside of holding the bike on an incline? I use it a bit when I race to adjust entry into corners sometimes when I am off a tad, but I never use it on the street above 30 MPH and rarely below 30 MPH, it's dangerous.

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Do you trust the hydraulics of your car ??
The original rear drum +hub is a huge lump of unsprung weight and unreliable :
sometimes it can lock up the rear wheel , and the next time it is non existent .
Each time you adjust the chain (and don't tell me about centering ) it is different .
Hot or cold , wet or dry .. always different , and THAT is dangerous .
Me likes to know what's going to happen when I push that brake pedal .
I have cars and bikes with drums and disks , and I like disk better .

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"Do you trust the hydraulics of your car ?"

Most cars don't sit for long periods of time, which is what causes hydraulic degradation.

As many have indicated using the rear brake on the street is not really the smart thing to do in the first place, and the rear drum on the Commando is more than sufficient for what one should do with a rear brake anyway. Plus, a correctly set up drum is just as consistent as a disk brake, if fact, some racers stayed away from disks because they enjoyed the consistency of the campagnolo 4 leading shoe brakes most were using in GP.

I find it hilarious that someone would be concerned about "un-sprung" weight on a 30 year old Commando, but really, how much of a weight difference is there anyway.

^^^^Unsprung weight has a lot to do with it. A Commando is pretty light compared to a CB750 so any weight shaved off our old Commandos would be a good thing I would think.

"you have mentioned hydraulic failure twice now, but I wonder how many have broken a rear brake cable :?:"

Actually, I have never had a broken rear brake cable on any street bike, which is understandable given my usage. I vaguely remember one rear brake cable failure on a motocross bike, but then rear brake usage is a different story in motocross.

"so any weight shaved off our old Commandos would be a good thing I would think."

Assuming that for the use you put your Commando a lighter bike will make a lot of difference.

How much more do you figure a rear drum and cable weigh compared to a rear disk, caliper/mount, master cylinder and plumbing?

All I am trying to say is that there are probably more cost effective upgrades than going from a rear drum to a disk.

I disagree with the most of the negative comments regarding rear brakes.

I use my rear brakes all the time, on all my bikes, on the street, roadracing, and in the dirt.

The FIRST TIME I ever had a tire leave the pavement in roadracing was on a borrowed H1 in Formula 500, with virtually no rear brakes. It was at Grattan, Michigan, just after getting totally airborne over the hump, I was a tad bit hot and couldn't make the right hander at the bottom using everything it had in the dual drilled front discs and what precious little it had in the stock rear drum. I just touched the grass and managed to keep it revving enough to buzz right back on the track and continue. Until I got in a few more races on the bike, I wasn't as fast as I could have been if I knew I had some rear brakes to work with.

They serve a very useful purpose and I wouldn't attempt to ride without them.

"They serve a very useful purpose and I wouldn't attempt to ride without them."

Good for you, but I recommend reliance on the rear brake on the street.

---28. Motorcycle riders in these accidents showed significant collision avoidance problems. Most riders would overbrake and skid the rear wheel, and underbrake the front wheel greatly reducing collision avoidance deceleration. The ability to countersteer and swerve was essentially absent. ---

The Hurt Report

http://www.magpie.com/nycmoto/hurt.html

That is. I DON'T recommend the use of the rear brake on the street.

montelatici said:

---28. Motorcycle riders in these accidents showed significant collision avoidance problems. Most riders would overbrake and skid the rear wheel, and underbrake the front wheel greatly reducing collision avoidance deceleration. The ability to countersteer and swerve was essentially absent. ---

The Hurt Report

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"Most riders"

I'm not like most riders. I KNOW how to use a rear brake.

Very nice and clean, Ron. Do you have a pix of the brake lever/ master cylinder too?

Don

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As promised I got out in the garage and snapped a few shots. However, I didn't roll the bike out as it is blocked in by a few others and my drive is still ice and snow covered.






It's a little hard to see (I didn't want it to stick out anyway), but it is a simple bracket made from a piece of scrap aluminum channel I picked up from the local re-cycler. A band saw, drill press, and buffing wheel did the trick. The master cylinder is a Brembo from a Ducati 900 that came with the rear caliper. It has a remote reservoir which is mounted above the rear fender.

By the way, the pictures are deceiving. There is plenty of room between the bracket and the chainguard.

How does the cable motion actuate the master cylinder plunger? Hard to tell from those shots.

montelatici said:

As many have indicated using the rear brake on the street is not really the smart thing to do in the first place, and the rear drum on the Commando is more than sufficient for what one should do with a rear brake anyway. Plus, a correctly set up drum is just as consistent as a disk brake, if fact, some racers stayed away from disks because they enjoyed the consistency of the campagnolo 4 leading shoe brakes most were using in GP.

I find it hilarious that someone would be concerned about "un-sprung" weight on a 30 year old Commando, but really, how much of a weight difference is there anyway.

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This is just my opinion, but track work is quite different to riding on the street. One seldom brakes as hard on the road as on the track, except in an emergency. A rear brake for the street should be able to assist in slowing you down in a variety of different traffic situations, and it should not have a tendency to lock up or fade. On damp, twisty roads, one will need to rely on the rear brake more to slow down and avoid losing the front end, and in these situations it needs to be progressive and predictable, and of course reasonably effective.

I have raced and ridden a variety of drum- and disc-braked machines, and I would choose a disc over a drum any day. Discs are generally more progressive and predictable, easier to maintain and much easier to set up. They are often a lot cheaper than a drum of equivalent stopping power. I've raced with a well set up TZ front drum (one of the finest drums ever made) but my current 10" Norvil disc and Lockheed caliper (on my classic racer) is superior and at a fraction of the price.

I guess in most normal street riding unsprung weight may not be that important, but if you're riding hard and trying to get the best out of the bike, too much unsprung weight can be a limiting factor.

Ron L, I like your brake pedal set up with the (JP Replica?) rear sets. Did you post pics of the disc and caliper/mounting previously?

"On damp, twisty roads, one will need to rely on the rear brake more to slow down and avoid losing the front end"

Sorry mate, that's exactly what the Hurt Report was talking about. I don't know how much racing you have done, but in the wet the rear brake is off limits. And yes, a front even disk single disk is superior to my TD-3 (TZ) front drum brake (but it is not close to a 4-leading shoe Campagnolo mounted on a Thruxton I had the opportunity to race), and if the regulations permitted I would put the same disk I have on my 350 Yamaha which is in a class that allows disk brakes. We are talking about a rear brake on a Norton driven on the street and the value of converting a rear drum on a non-Mark III to a drum. Do you really believe it is worth the cost, time and effort to add to a bike that sits for long periods another hydraulic system when the rear drum brake is more than adequate for the street?

With a mk111 hub is the weight in the
1/heavy iron disc
2/large steel caliper bracket
3/and that great big heavy sprocket and cush drive[thats all one unit is it :?: ]

is the hub itself heavy, the disc, caliper and carrier would be easy to replace but is there any replacement for the sprocket arrangement.
I haven't ruled out any suggestion yet, I keep thinking mk111 hub keeps it NORTON,The trail bike idea is good, but all the wreckers now seem to want you to order parts online, so I can't wonder down and eye up 1/2 dozen different hubs and annoy the crap out of them.
The MANEY idea with the 4 bolt TRIUMPH hub and his cush drive doesn't look like a bad idea, it'a all decisions and money now, and I can't make either.

Thanks for the photo's and replies

Well, to point out the use of the rear brake as a cause, after the inexperience cause, which I would think is intuitive, means something.

But the point is, do you really think that converting a perfectly good rear drum to a disk system on a pre Mark III is a wise way to spend one's time and money on a Commando compared to a belt drive, a head job, an upgraded front disk brake system, Mark III isos,etc. That's my point. Look I have a Mark III with a rear disk, so anything I say has nothing to do with what I have/use.

montelatici said:

Well, to point out the use of the rear brake as a cause, after the inexperience cause, which I would think is intuitive, means something.

But the point is, do you really think that converting a perfectly good rear drum to a disk system on a pre Mark III is a wise way to spend one's time and money on a Commando compared to a belt drive, a head job, an upgraded front disk brake system, Mark III isos,etc. That's my point. Look I have a Mark III with a rear disk, so anything I say has nothing to do with what I have/use.

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I don't think there is any use in questioning unreasonable spending when it comes to these bikes. I mean, have you seen some of these bikes? :mrgreen:

"I don't think there is any use in questioning unreasonable spending when it comes to these bikes. I mean, have you seen some of these bikes?"

Well, I guess if one has unlimited funds one could undertake almost any upgrade, maybe even applying shaft drive. My point is that there are far more useful upgrades than changing over a perfectly good drum brake on the rear. On the front, I would agree that a disk conversion is an excellent upgrade if you have an old 750.

montelatici said:

But the point is, do you really think that converting a perfectly good rear drum

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That it ain't

montelatici said:

a head job

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done

montelatici said:

an upgraded front disk brake system

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done

montelatici said:

Mark III isos,

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done
good headsteady, rearset controls, good tyres,adjustable koni shocks, low bars, fork brace
done
I have one of Mr Boulds damper kits coming so thought it would be a good time to shed some wheel weight to help it all out and I feel a disc system is easier to maintain and would really like to dump the fixed sprocket drum arrangement

I have just seen your pics Ludwig
does the sprocket have rubber inserts in the bolts :?: as cush drive
would you have been able to fit smiths speedo drive between disc and carrier :?:

How does the cable motion actuate the master cylinder plunger? Hard to tell from those shots.

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Look close in the first picture. The bolt on section of angle holds the outer cable housing nipple and the cable end acts on the end of a simple bellcrank which changes the motion from pull to push on the mastercylinder pushrod. Not an elegant solution, but with my caveman tools it works.

Did you post pics of the disc and caliper/mounting previously?

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Yes, this is old news to most here. I have the same front and rear brake setups on two of my Commandos.