The Dunstall twin disc set-up had the calipers cast into the fork sliders. The set-up was reckoned to be ineffective (and expensive) IN PERIOD. It might be improved with a smaller diameter master cylinder, but you would be hard pressed to find one to find out - few were sold. If any survive, they are probably stashed under work-benches.
Installing a Front Disc Brake on a Series ‘C’
- Thread starter CarlHungness
- Start date
The Dunstall twin disc set-up had the calipers cast into the fork sliders. The set-up was reckoned to be ineffective (and expensive) IN PERIOD. It might be improved with a smaller diameter master cylinder, but you would be hard pressed to find one to find out - few were sold. If any survive, they are probably stashed under work-benches.
With the hoses at the top it is easier to bleed the calipers back to the master cylinder instead of out of the bleed nipples, air tends to rise anyway. Just push the pistons back one caliper at a time.
I think the twin Honda Superdream discs are about the neatest, and almost the correct bore and offset as well.
I think the twin Honda Superdream discs are about the neatest, and almost the correct bore and offset as well.
If you are going for Superdream brakes, use the larger 250N discs not the 400N ones. Twin smaller discs on the 400. There may be period discs of larger size but same offset, perhaps on the CB900F
I've been following this thread with interest and have researched this subject (and other ideas to improve my Rapide) almost to death!
I'm nearly finished putting disc om my bike and feel it's about time I threw my hat in the ring as I may be able to help a little, after all, without the help of you lot (Vincent riders generally) I would have even more to work out by mainly guesswork..
So like I said I'm not completely done yet but I can keep you all posted, I'll even take some pictures later (soon)
Discs.. yes Honda 250... 'correct' offset and 5 hole pattern, centre bore is about 20 thou small. easy. I drilled 5 more holes and made a thin sheet ally cover ring for the other 5 holes, I trimmed a flat off a set of 5 new bolts as you need slightly long mounting bolts.
I then made ally plates to support the stock speedo drive and hide the Honda disc centres. I had to build a boss to move the drive box outboard slightly but the gears line up now. Also on the 'cover' plates there is a boss to line up with the fork leg stop, this boss is centre bored to locate with the caliper bracket 'stop peg'
I used Kawasaki Zepher calipers (I would have like opposed piston calipers but I need spoke clearance and moving the discs out I lost alignment for the speedo drive) as the mounts on the caliper are not handed, only the floating two piston caliper, which has a bleed nipple at the top for easy bleeding. The caliper bracket is 6 mm ally pivoting on stainless counter-bored spacers on the new 4140 axle. 'stop pins' are also stainless locating on special 'top-hat' threaded plugs that locate into the brake disc cover plates (the cover plates don't really rotate as they are held but the axle tightening but I figured they would be better pinned as the speedo drive needs to stay in one place. (the left side disc cover is just a cover.. although in black with un-drilled disc is does look a little less modern) The front fender stay is bolted in the same place on the fork leg, the bolt going through the caliper bracket as it may stop the caliper dropping down, but its not in any tension either way. the other fender stay is off a welded lug on the caliper bracket, I didn't like the fender stay going around or bending over the caliper.
My ideas aren't totally original I admit, like I said I research a LOT before using the best ideas and making them work for me. It really is quite a bit of work but I believe it looks and should (I've not tried it yet on the road, other work I'm doing as well, including Normans Steering head mod and AVOs)
Yes, I know someone will ask for pics and I will post some.
While I'm here I will thank Everyone in the VOC and all Vincent owners for being so willing to share their experience and advice.. believe me, it's valuable and appreciated, and a lot more useful than the nonsense I've read on Harley and BMW forums, (yes, I have a couple Harleys and a BMW, old bikes not those new fangled things!)
I'm nearly finished putting disc om my bike and feel it's about time I threw my hat in the ring as I may be able to help a little, after all, without the help of you lot (Vincent riders generally) I would have even more to work out by mainly guesswork..
So like I said I'm not completely done yet but I can keep you all posted, I'll even take some pictures later (soon)
Discs.. yes Honda 250... 'correct' offset and 5 hole pattern, centre bore is about 20 thou small. easy. I drilled 5 more holes and made a thin sheet ally cover ring for the other 5 holes, I trimmed a flat off a set of 5 new bolts as you need slightly long mounting bolts.
I then made ally plates to support the stock speedo drive and hide the Honda disc centres. I had to build a boss to move the drive box outboard slightly but the gears line up now. Also on the 'cover' plates there is a boss to line up with the fork leg stop, this boss is centre bored to locate with the caliper bracket 'stop peg'
I used Kawasaki Zepher calipers (I would have like opposed piston calipers but I need spoke clearance and moving the discs out I lost alignment for the speedo drive) as the mounts on the caliper are not handed, only the floating two piston caliper, which has a bleed nipple at the top for easy bleeding. The caliper bracket is 6 mm ally pivoting on stainless counter-bored spacers on the new 4140 axle. 'stop pins' are also stainless locating on special 'top-hat' threaded plugs that locate into the brake disc cover plates (the cover plates don't really rotate as they are held but the axle tightening but I figured they would be better pinned as the speedo drive needs to stay in one place. (the left side disc cover is just a cover.. although in black with un-drilled disc is does look a little less modern) The front fender stay is bolted in the same place on the fork leg, the bolt going through the caliper bracket as it may stop the caliper dropping down, but its not in any tension either way. the other fender stay is off a welded lug on the caliper bracket, I didn't like the fender stay going around or bending over the caliper.
My ideas aren't totally original I admit, like I said I research a LOT before using the best ideas and making them work for me. It really is quite a bit of work but I believe it looks and should (I've not tried it yet on the road, other work I'm doing as well, including Normans Steering head mod and AVOs)
Yes, I know someone will ask for pics and I will post some.
While I'm here I will thank Everyone in the VOC and all Vincent owners for being so willing to share their experience and advice.. believe me, it's valuable and appreciated, and a lot more useful than the nonsense I've read on Harley and BMW forums, (yes, I have a couple Harleys and a BMW, old bikes not those new fangled things!)
Andrew,
We are all very lucky if our mods are derivative. There has been so much good work that has been done by others. Different designs are just that...different. If something clicks with you, use it...if not, don't use it.
One of the best mods you have done is to fix the Girdraulic with a new stem (or short springs). That was one of the problems that I ran into with disc brakes on a Vincent. Norman noticed the same thing when riding a Vincent with a disc brake.
Best of luck!
David
We are all very lucky if our mods are derivative. There has been so much good work that has been done by others. Different designs are just that...different. If something clicks with you, use it...if not, don't use it.
One of the best mods you have done is to fix the Girdraulic with a new stem (or short springs). That was one of the problems that I ran into with disc brakes on a Vincent. Norman noticed the same thing when riding a Vincent with a disc brake.
Best of luck!
David
Up-date on the Caliper mounting, actually a small warning (advice really) to anyone thinking of pursuing the 'dream' of better (a lot better than most drum brakes I think) brakes....
Aligning the mounts... not at all easy, at least if you want the brakes to work properly, I guess you could mount the calipers so sloppy that they literally float into alignment, good idea but you'd need a Lot of brake lever travel to take up the 'play' before the brake actually starts it's braking job...
A caliper mount needs to be aligned straight and square to the disc, no twist or binding or things don't work, and our point is to have more than just a slightly better brake. By the way, one disc can be enough, again if it works properly, a larger disc is better (swept area, heat dissipation etc) Oh, and discs in the wet? never a problem, a brake pad will dry and warm a disc instantly! An advantage for us fitting a single disc would be that the stock speedo drive could be used on the other side to the disc and a flat disc can be sourced, and easier to mount than finding a suitably dished disc. Single discs work fine, with negligible fork flex in use, ie slowing and stopping.. although fork twist can seem alarming on ,say, a Harley "Wide Glide" (especially with extended forks) if you hold the brake lever and 'bounce' a stationary machine... on the road, like I said, not noticeable at all (in normal operation)
I don't really see a problem with discs on a Brampton, probably the suspension and damping will get a bit out of shape but the real problem would more likely be just the stresses on the 70 year old forks, and they really weren't designed with those stresses involved... try running into the car with ABS in front of you and see the effects of old girders succumbing to a bit of forced retardation....
Anyway, back to the immediate issue, alignment of the calipers... I found the caliper can only be tightly held by the axle, when the axle nut is tightened the mount is rigidly held in a 'sort of' square plane to the axle, except only 'sort of' as when the forks were made by the factory the machining of the axle hole faces were not necessarily perfectly square (to the axle) or even parallel, even the two fork blades are not perfectly parallel to one another, with drum brakes this is not so critical. For correctly functioning disc brakes alignment is very important.
So the 'stop-pin' needs some 'float' and the fender mounting bolt which was going through the mount was holding the mount slightly skew, this had to be modified with a shouldered spacer with some lateral play, the fender mounting bolt now has only that job to do, it never was in tension in any direction before, as I said, but now it's not interfering with the caliper mounting.
However, I still haven't completed the job, and many may be put off this task... I'm sure the "Dutch" brake or even the 8" unit is adequate, but I have been set on this route for a while.
My thought has also always been that the suspension/steering needs modification if the full potential of better braking performance is to be realized, yes quite likely this the real issue with Bramptons. Again I thank Norman, and AVO (and Thornton etc of course) for their constant striving to improve the Vincent.
I can imagine the PCV thinking he should improve the brakes but knowing the limitation of the stock fork design he hoped we'd all just plan ahead when stopping is involved..
"bloody hell! this geezer goes on..." I hear you say...
Aligning the mounts... not at all easy, at least if you want the brakes to work properly, I guess you could mount the calipers so sloppy that they literally float into alignment, good idea but you'd need a Lot of brake lever travel to take up the 'play' before the brake actually starts it's braking job...
A caliper mount needs to be aligned straight and square to the disc, no twist or binding or things don't work, and our point is to have more than just a slightly better brake. By the way, one disc can be enough, again if it works properly, a larger disc is better (swept area, heat dissipation etc) Oh, and discs in the wet? never a problem, a brake pad will dry and warm a disc instantly! An advantage for us fitting a single disc would be that the stock speedo drive could be used on the other side to the disc and a flat disc can be sourced, and easier to mount than finding a suitably dished disc. Single discs work fine, with negligible fork flex in use, ie slowing and stopping.. although fork twist can seem alarming on ,say, a Harley "Wide Glide" (especially with extended forks) if you hold the brake lever and 'bounce' a stationary machine... on the road, like I said, not noticeable at all (in normal operation)
I don't really see a problem with discs on a Brampton, probably the suspension and damping will get a bit out of shape but the real problem would more likely be just the stresses on the 70 year old forks, and they really weren't designed with those stresses involved... try running into the car with ABS in front of you and see the effects of old girders succumbing to a bit of forced retardation....
Anyway, back to the immediate issue, alignment of the calipers... I found the caliper can only be tightly held by the axle, when the axle nut is tightened the mount is rigidly held in a 'sort of' square plane to the axle, except only 'sort of' as when the forks were made by the factory the machining of the axle hole faces were not necessarily perfectly square (to the axle) or even parallel, even the two fork blades are not perfectly parallel to one another, with drum brakes this is not so critical. For correctly functioning disc brakes alignment is very important.
So the 'stop-pin' needs some 'float' and the fender mounting bolt which was going through the mount was holding the mount slightly skew, this had to be modified with a shouldered spacer with some lateral play, the fender mounting bolt now has only that job to do, it never was in tension in any direction before, as I said, but now it's not interfering with the caliper mounting.
However, I still haven't completed the job, and many may be put off this task... I'm sure the "Dutch" brake or even the 8" unit is adequate, but I have been set on this route for a while.
My thought has also always been that the suspension/steering needs modification if the full potential of better braking performance is to be realized, yes quite likely this the real issue with Bramptons. Again I thank Norman, and AVO (and Thornton etc of course) for their constant striving to improve the Vincent.
I can imagine the PCV thinking he should improve the brakes but knowing the limitation of the stock fork design he hoped we'd all just plan ahead when stopping is involved..
"bloody hell! this geezer goes on..." I hear you say...
I guess it might how we ride, But I have had some sick making times with Cold discs as well as Wet discs.
Always thought they were a bit of a Con', Cheap to make etc.
Maybe good when things get too hot ie Fade, But the way some of them rust etc.
Cheers Bill.
Always thought they were a bit of a Con', Cheap to make etc.
Maybe good when things get too hot ie Fade, But the way some of them rust etc.
Cheers Bill.
Dear Bill,
I've also come across discs in the past that are not great in the rain.
Early disc brakes on bikes were often cast iron that indeed did go a bit rusty. I remember early MotoGuzzi had iron discs. Perhaps a bit of rust gave the pads something to grab on. Later stainless or non-rusting materials were used some of which were just as bad when wet. Most discs used now are drilled which makes them lighter and helps dissipate any water. The right pads to match the disc material makes a big difference to working in the wet and having minimal fade.