Rear hub drum to disc conversion

splatt · Feb 16, 2010

Does any one have any suggestions, I want to rebuild some wheels with alloy rims ect, but don't really want to waste my money lacing up a hub with a POS brake, MK111 would be the easist would it, but have heard they are bit heavy :?: :?: . I would like to get away with keeping the swing arm mods to a minimum, ie. not having to open up the fork end , only so that a standard wheel could fit back in , but that isn't to critical, as I have a spare swing arm.
Wreckers are a bit scarce, so I can't wonder down and eye ball up different hubs. Making new axles mounting plates ect, isn't a problem,speedo drive might may be a bit tricky though.
Yes I know if every thing is sent off to VINTAGE BRAKE it will come back working, the 40000 km round trip doesn't really seem worth it.
Photos really help my small brain capacity
thank guys

grandpaul · Feb 16, 2010

Piece of cake. Use a Mark III rear wheel and you're all set as long as you cut the inside tail end of the swingarm tube back to a point just aft of where it mates to the axle web, then weld it all up with some reinforcement to duplicate the inside of a Mark III swingarm.

-OR-

Just bolt up a complete Mark III rear end!

Next, you'll have to fabricate a left foot master cylinder setup; there are dozens of ways to do this using a modern m/c.

bpatton · Feb 16, 2010

GP, didn't Kenny Dreer use a 4 bolt Trumph hub on his VR880? They had a great cush drive on them if I recall. Steve Maney has a cush drive on his site.
http://www.stevemaney.com/products/Cush ... 20unit.jpg
It uses a 4 bolt Triumph hub too and I'm sure he's got a brake setup that works with it. If it came to it, EBC makes custom disc/carriers with whatever offset and bolt pattern you need and hanging a Brembo w/ anchor arm wouldn't be that hard. Check out flat track racing supply sites too.

grandpaul · Feb 16, 2010

Well, I have a VR880 rear hub set aside with a deposit, with Kenny (I'm buying out all his remaining VR880 stuff).

I can have a look at some photos he sent a while back.

I'll pass it on for 10% over cost + postage; I have no plan to use it

MexicoMike · Feb 16, 2010

Is it worth the bother? Certainly a disc would be a better brake but virtually all the stopping is done up front and the oem drum can lock up the rear anyway so I don't see how you would achieve better actual braking performance by replacing it. Sure, it would be a better feel since there would be less overall pedal movement with the hyd disc as opposed to the cable drum but it won't shorten your stopping distance. Many riders, including some racers, don't use the rear brake at all. Sport Rider did a test and got the following results (don't know the actual bike speed for the test):

REAR BRAKE ONLY: 289 FEET
FRONT BRAKE ONLY: 151 FEET
BOTH BRAKES: 146 FEET

The minimal contribution of the rear means that as far as performance is concerned, the drum is more than adequate. Of course, putting a disc back there would give the bike an "updated" look.

Chris · Feb 16, 2010

Hi Mike
I think you have just answered your own question there!
Nothing to do with better braking!
Mine was a special so why not change it? However as a user of the rear brake just to settle the plot the reduced weight & the ease of swapping alloy 520 sprockets is a must.
all the best Chris

prmurat · Feb 16, 2010

I did this on mine: mkiii wheel with a cut disc, r6 yam caliper and some work on the left brake pedal...

Philippe

MexicoMike · Feb 16, 2010

"Nothing to do with better braking!
Mine was a special so why not change it?"

Totally agree and that's a darn good reason to change it!

"MM : a rear brake is not only usefull to stop the bike .
It helps to keep the rear end in check ..to keep the chain under tension .
Hard to explain , but I am shure anyone who ever rode a Commando fast over twisty roads knows what I mean ."

I totally agree with that as well. But performance wise, again the oem drum rear will do this just fine. I use only the rear brake quite frequently for low speed maneuvering, it allows you to tighten your turns at parking lot speeds. So I don't mean to sound as if I'm putting down using a rear brake at all.

splatt · Feb 16, 2010

MexicoMike said:
performance wise, again the oem drum rear will do this just fine.

Mike are you sure you are using a commando rear brake :?: your performance description sounds wrong

4 bolt meridan triumphs dont have a cush drive do they :?:

ludwig said:
Hard to explain , but I am shure anyone who ever rode a Commando fast over twisty roads knows what I mean

Thats one of the reasons I want a rear brake, I only ride one way on twisty roads

grandpaul said:
Well, I have a VR880 rear hub set aside with a deposit, with Kenny (I'm buying out all his remaining VR880 stuff).

I can have a look at some photos he sent a while back.

I'll pass it on for 10% over cost + postage; I have no plan to use it

I wouldn't mind a look GP

thank guys

RennieK · Feb 16, 2010

Kenny used Sertco cush drives. Sertco made them before anyone else did and I think they licenced the technology to all the other bike companies and quit making them themselves. They no longer have them on their web site and as i recall they have a statement about that on their site. Steve Maney's look quite different from the Sertco ones. Steve's work with the 4 bolt triumph hubs. The Norton MarkIII seem like the best with the long diagonal contact surface although my opinion is based entirely on appearance with no actual experience hands on. Steve and Kenny both have easily changeable sprockets though which is huge over the Norton sprocket setup which is one piece with the paddles. It will be impossible to get new rubbers for the Sertco units unless you make your own. I think Ludwig has the right idea, find a nice lightweight metric bike with a cush drive hub with 2 piece hot swap sprockets and you're stylin.

Rob94010 · Feb 16, 2010

Philippe, I saw your bike out at Farley's. It was a beautiful rider. Did you have a hydraulic clutch set up on there? Nice to know you and your bike are on the mend.

prmurat said:
Philippe

grandpaul · Feb 17, 2010

splatt said:
I wouldn't mind a look GP (at Dreer VR880 rear hub)

Ron L · Feb 17, 2010

splatt said:
Does any one have any suggestions, I want to rebuild some wheels with alloy rims ect, but don't really want to waste my money lacing up a hub with a POS brake, MK111 would be the easist would it, but have heard they are bit heavy :?: :?: . I would like to get away with keeping the swing arm mods to a minimum,

This was a pretty easy conversion. A MkIII wheel and swingarm with a Ducati 900CR rear caliper, rotor, and mount. It replaces the heavy Norton rotor with a lighter Brembo, the caliper is much lighter, and the steel MkIII caliper mount is replaced with the aluminum Ducati one. Pares a lot of weight off the MkIII setup. I made a bracket for the Brembo master cylinder and mounted it to the rear frame plate on the left side (vertically) and used a shortened rear brake cable to actuate the cylinder. Of course, I have a matching front Brembo 4-pot caliper and 300 mm floating rotor.

Deckard · Feb 18, 2010

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

Don

RennieK · Feb 18, 2010

Did the rotor attach to the hub easily? I can't imagine it has the same bolt pattern as the stock rotor.

prmurat · Feb 18, 2010

Yes Bob...Farley's and hydraulic clutch...it was me...maybe the day we came back from LA with some friends?
Philippe

montelatici · Feb 18, 2010

splatt said:
Does any one have any suggestions, I want to rebuild some wheels with alloy rims ect, but don't really want to waste my money lacing up a hub with a POS brake, MK111 would be the easist would it, but have heard they are bit heavy :?: :?: . I would like to get away with keeping the swing arm mods to a minimum, ie. not having to open up the fork end , only so that a standard wheel could fit back in , but that isn't to critical, as I have a spare swing arm.
Wreckers are a bit scarce, so I can't wonder down and eye ball up different hubs. Making new axles mounting plates ect, isn't a problem,speedo drive might may be a bit tricky though.
Yes I know if every thing is sent off to VINTAGE BRAKE it will come back working, the 40000 km round trip doesn't really seem worth it.
Photos really help my small brain capacity
thank guys

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.

Ron L · Feb 18, 2010

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

Can't say I disagree. For me I had this spare Mk3 wheel setup with a swingarm and one thing led to another. I would not spend the money sourcing the parts for the conversion for any performance advantage. My Brembo setup definitely saves weight over the stock Mk3, so it was a clear choice for my Mk3. Converting the '74 to a disc was a very questionable move.

Did the rotor attach to the hub easily? I can't imagine it has the same bolt pattern as the stock rotor.

The Brembo bolt circle is larger than the Norton, so a simple disc of aluminum was used to make an adaptor. It can be seen in the photo.

Do you have a pix of the brake lever/ master cylinder too?

I had a couple, but I can't seem to find them. I'll try to post a couple new ones this weekend.

montelatici · Feb 19, 2010

I guess some people ride a bit more on the edge on the street than I do. I never ride hard enough on the street to engage the rear brake to induce drift for entry adjustment or settling. But yes, on the track it is useful and both my race bikes have drum rears which are more than sufficient. Granted, the Yamaha rear racing drums on are larger diameter, than the older Commando front drum, if single shoe. I remember losing front disk hydraulics at Road Atlanta one year and had to finish the race on only the rear brake. What a bummer to watch bikes passed in the early laps go by easily 4-5 laps from the finish.

splatt · Feb 19, 2010

montelatici said:
I remember losing front disk hydraulics at Road Atlanta one year and had to finish the race on only the rear brake[/quote

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

Rear hub drum to disc conversion

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