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Installing a Front Disc Brake on a Series ‘C’


highbury731

Well Known and Active Website User
VOC Member
The most powerful drum brake of all time is the duo-servo brake.

View attachment 21333
It was not a popular brake, but it is superior to double twin leading shoe brakes in performance. It is considered a single leading shoe brake by racing organizations. It is not very popular because it is wildly unstable, but if set up properly it will probably out-perform a big twin disc. This brake design was also used extensively in cars and hydraulically operated.

David
John Surtees had one of these Seeley front brakes on the front of a Vincent. I have been wanting to find out how the brake shoes and adjustment were designed on this hub. A quick internet search reveals that Molnar offer them, a snip at £1850 + VAT..... I have seen replica Ceriani 230mm 4ls brakes offered for a very similar sum. Are the Seeley brakes really comparable?

FWIW this arrangement of linked brake shoes can be found on bicycles for small children, usually Continental ones. They are very good for small hands without much strength.

Paul
 

vibrac

Well Known and Active Website User
VOC Member
Almost the diameter of the stirrup rim brakes on my 1925 Douglas:rolleyes: now you really have to plan your stopping distances on that
I do have an upgraded the back brake though - the shoe that rubs in the belt rim it was once a mahogany chair leg:eek:
 

vibrac

Well Known and Active Website User
VOC Member
Now that it becomes clear that fitting a disc brake is not a substantial modification as far as the 40 year mot is concerned I can revisit this subject.
For a comet it would seem from the above that a single disc with a matching caliper and lever mounted on the LH side with a plate and Speedo drive on the RH side is the way to go (however if you have tried that and decided double is better even for a comet let me know)
if anyone has details of this mod pictures plans etc of a working installation it would save me and anyone else on this path some time to say the least.
i have a new steering stem girdraulic fork installation a lathe and a mill
 

BigEd

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VOC Member
VOC Forum Moderator
Now that it becomes clear that fitting a disc brake is not a substantial modification as far as the 40 year mot is concerned I can revisit this subject.
For a comet it would seem from the above that a single disc with a matching caliper and lever mounted on the LH side with a plate and Speedo drive on the RH side is the way to go (however if you have tried that and decided double is better even for a comet let me know)
if anyone has details of this mod pictures plans etc of a working installation it would save me and anyone else on this path some time to say the least.
i have a new steering stem girdraulic fork installation a lathe and a mill
Dear Tim,
I have sent you an email with a link regarding a conversion.
 

timetraveller

Well Known and Active Website User
VOC Member
Would you chaps copy me in on this please. Someone who bought one of the new steering heads has left me a set of girdraulics, a front wheel with purpose made 320 mm discs and the hydraulics. He would like me to design, and get made, all the bracketry. It would ease the pain if we could come up with a design suitable for more than one person. Note that the discs were made specially to fit the Vin hub.
P4130261.JPG
 

peter holmes

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VOC Member
I missed getting one of the Dave Lambert kits, when I decided that I wanted a kit Dave had just sold his last one, no amount of pleading would cajole him to make just one more, I think Dave's kit was Honda 250N based. I have always thought that it would be great if there was a source we could just go to a purchase a tried and tested kit, I am sure 10 kits would sell immediately, maybe even 50, over to you Norman?
 

davidd

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VOC Member
Norman,

I think a universal design is a little difficult, but you look to have a very easy set-up to work with. I would do a variation of this:
Disc Caliper to Girdraulic.GIF
This is a flat plate. The lower hole is the axle hole. The plate thickness here is the thickness of the E80 nut and the stock brake plate thickness together.

The hole directly above the axle hole is the brake anchor. I put a SS bolt through hear and used it to bolt the plate in place. The curve in the outline of the plate, above and to the right of the anchor is to clear the lower spring box mount.

The remaining two holes are the caliper mounting holes. They were close to the blade on this design, but on yours, it is such a big disc that you have plenty of room to the left. I would keep the caliper close just to minimize the weight of the plate.

Finally, I milled the back of the plate to get the calipers to align properly with the disc. I think I used an overly thick plate that put the calipers in the right place and milled the remainder of the plate to the E80 nut and brake plate thickness. You may want to try out a flat piece of aluminum to make a fitting to calculate the caliper mounting offset relative to where the E80 nut and brake plate thickness are located. I used 4130 steel for the plate itself. I probably could have used 2024 aluminum, but I was being conservative.

It looks to me like the caliper in the photo is in a good place for the plate right now. The spring box is a little further forward when mounted on the eccentric, so I would move the caliper a little further forward.

Thus, the plate is in a fixed position and a fixed thickness where it replaces the brake plate and nut. The thickness of the rest of the plate will have to move slightly in or out depending on what the calipers want.

David
 

timetraveller

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VOC Member
Thanks David. This was not a project I was looking for. The owner left it with me to get someone else who has both machining and design facilities to sort it out. Unfortunately after two days that person asked me to take it away so either I do it or it gets abandoned. I like the fact that the owner got the disc manufacturers to make the disc specifically to fit a Vin which should allow a neater job but I am still trying to wind down the steering head job, it turned out to be 60 in the end, giving a five year total of about 140 out there, and I would like to get my own bike on the road. The old adage used to be "so many girls, so little time". This has now tuned in to "so many jobs, so little time". Could this be old age??o_O
 

vibrac

Well Known and Active Website User
VOC Member
Thank you all for the input on and off forum my thoughts are firming up round Half of a Kwaker disc I will feed back but it will be some time as mid season is a busy time
 

stumpy lord

Well Known and Active Website User
VOC Member
Carl,
I've been considering the same project for awhile myself, just haven't got around to it. Anyway, here are some pictures and articles I've collected on the subject. I believe I got them from www.thevincent.com some time ago. Don't know if you already have them or not hope they help. I would be interested in seeing what you come up with.
Steven
Hi,
the set up with the grimeca callipers is the Dave lambert set up and utilises Honda 250n discs.
regards norman
 

Dave61

Well Known and Active Website User
VOC Member
Norman,

I think a universal design is a little difficult, but you look to have a very easy set-up to work with. I would do a variation of this:
View attachment 22433
This is a flat plate. The lower hole is the axle hole. The plate thickness here is the thickness of the E80 nut and the stock brake plate thickness together.

The hole directly above the axle hole is the brake anchor. I put a SS bolt through hear and used it to bolt the plate in place. The curve in the outline of the plate, above and to the right of the anchor is to clear the lower spring box mount.

The remaining two holes are the caliper mounting holes. They were close to the blade on this design, but on yours, it is such a big disc that you have plenty of room to the left. I would keep the caliper close just to minimize the weight of the plate.

Finally, I milled the back of the plate to get the calipers to align properly with the disc. I think I used an overly thick plate that put the calipers in the right place and milled the remainder of the plate to the E80 nut and brake plate thickness. You may want to try out a flat piece of aluminum to make a fitting to calculate the caliper mounting offset relative to where the E80 nut and brake plate thickness are located. I used 4130 steel for the plate itself. I probably could have used 2024 aluminum, but I was being conservative.

It looks to me like the caliper in the photo is in a good place for the plate right now. The spring box is a little further forward when mounted on the eccentric, so I would move the caliper a little further forward.

Thus, the plate is in a fixed position and a fixed thickness where it replaces the brake plate and nut. The thickness of the rest of the plate will have to move slightly in or out depending on what the calipers want.

David
David,
I`ve been working on a disc brake conversion, I`ve had two adapters made to suit the front hub & Kawasaki discs from a ZX6 & had seen your suggestion for the caliper plate so bought an unthreaded hollow axle but then realised that the bearings would be not have the nuts to retain them which I believe was the case with Lightnings, but as I`m unfamiliar with the set up I can`t get my head around having loose outer races, could you shed some light on wether I`ve got that right.
I`ve got a pair of Billet 6 pot calipers left over from a previous project and whilst I appreciate they are overkill they are a very slim caliper so no issues with spoke clearance.
A pair of their 4 pot ones would be very neat & compact, perhaps I should get my hacksaw out !
 

Attachments

Bill Thomas

Well Known and Active Website User
VOC Member
Percy Tate ?, Old Triumph Racer, Thought putting the Caliper behind the legs is best for balance with the forks,
I think it improved the steering on old Yamaha's.
The L/ning brake plates are thicker than the steel ones, Don't need nuts, As long as what ever you have from the wheel bearing out wards is a nats longer than the hollow axle, It is all held together by the wheel spindle clamping the fork legs.
Cheers Bill. P.S. The Bike looks Good.
 

Dave61

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VOC Member
Percy Tate ?, Old Triumph Racer, Thought putting the Caliper behind the legs is best for balance with the forks,
I think it improved the steering on old Yamaha's.
The L/ning brake plates are thicker than the steel ones, Don't need nuts, As long as what ever you have from the wheel bearing out wards is a nats longer than the hollow axle, It is all held together by the wheel spindle clamping the fork legs.
Cheers Bill. P.S. The Bike looks Good.
Thanks for that Bill,nice to have advice from someone with a bit of experience.
I prefer the idea of the caliper behind as well, going to make a ply template as I`m a Chippy then get it machined up locally.
 

davidd

Well Known and Active Website User
VOC Member
Dave,

Yes, Bill has explained it. From a production point of view Vincent designed the wheels so the E80 nuts kept the wheel together as one piece. The E80 nuts snug up the bearings and the axle being tightened is just piling on, so to speak, as it is doing the same. When the racers were designed Vincent needed to make the backing plates thicker and lighter. They could make the plate the entire thickness of the old braking plate thickness plus the E80 nut. This could be done because they could use the axle being tightened in lieu of the E80 nuts.

This is the same design I am suggesting for the caliper plates. You have the the backing plate thickness and the E80 nut thickness to use for your caliper mounting plate. The fork won't notice a thing.

It may be a little over-kill, but you should use the size brakes from a modern machine that is hauling down a 500 lbs. motorcycle for a twin, or a 420 lbs modern bike for the Comet. That is the easiest way to size them.

David
 

BigEd

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VOC Member
VOC Forum Moderator
David,
I`ve been working on a disc brake conversion, I`ve had two adapters made to suit the front hub & Kawasaki discs from a ZX6 ........... I`ve got a pair of Billet 6 pot calipers left over from a previous project and whilst I appreciate they are overkill they are a very slim caliper so no issues with spoke clearance.
A pair of their 4 pot ones would be very neat & compact, perhaps I should get my hacksaw out !
The six-pot callipers might as you say may be overkill. I used the two-pot callipers from a Kawasaki Zephyr and they provide adequate stopping power on a Rapide. The leverage ratio of master cylinder piston diameter/area to pot pistons diameter/area is quite important to get a decent brake feel, not enough and the brake is wooden and too much makes it not so easy to modulate. I got the master cylinder that was originally fitted with the callipers I used so the ratio is correct. If you are using a different master cylinder they often have a size cast into the body that can be helpful.
left_caliper_close_up_compressed.jpg
 

andrew peters

Website User
VOC Member
I have a pair of Brembo Goldline four pots but with the discs I have (Honda 250N) and spoke wheels I don't have the clearance.. so those calipers will go on another project.. beside, really, a little overkill on the light Vincent..
 

andrew peters

Website User
VOC Member
Here as promised, pictures of my disc brake conversion.. a lot of work, thought and experiment... hardly a 'kit' to put together and bolt on, getting clearances etc and looking right.. oh and functioning well.. Thing is of course, like many of us I'm so busy with other projects, and making money to finance those projects... ZX10 calipers, Honda 250N discs, stock speedo drive.. all parts in stainless and dural (1430 axle) and made in my shop here.. lower mudguard support (still at powdercoat) is attached to lug on back lower corner of caliper bracket as I didn't like the support arm reaching around or over the caliper
 

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Bill Thomas

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VOC Member
I put a Norton disc on the back of my Special, Went on very easy, The only problem was it was too good !,
I drilled holes in the small pads !,And drilled the Disc, And made lots of smaller and smaller levers on the M/cylinder.
Cheers Bill.
 
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