Hitchcocks Forum

I have pretty much all the parts I need to convert a drum brake 500 bullet to disc using an EFI wheel and a pricol calliper. I did have a different wheel and a brembo calliper but I still can't ID the wheel and the calliper doesn't fit with the EFI wheel (spoke angled differently and foul it).



Anyway, Got the wheel in and mudguards lined up so all I need is a bracket to fit the calliper to the fork. It's a simple cut-out bit of sheet steel however the hole positions are tricksy, two pairs of holes offset in 2 planes. I've asked our hosts if they can supply a bracket by itself but they can't. I've done an approximation based on my best guess but there could be a lot of bits of scrap steel with 4 slightly differently placed holes in in my scrap bin by the end of this process.



I wondered if anyone had one they would be prepared to draw round and post me the tracing so I can get the hole centres right? I'd be prepared to forward you some cash for your trouble.

you probably know that this is the bracket you’ll need.






i had one of those but threw it away, for the simple fact that the brake needs to be correct in both axes.

and you’ll be attaching the bracket to two tabs that where never mend to serve this purpose.

so the are no straight at all.

the alignment needs to be less than a 1/10 of a millimeter or the brake will constantly drag, even to a point of running hot and locking up the wheel.



also have you had the change to look at a lower leg of a original brake version bullet, they are quite a bit more beefed up at the point where the caliper is fixed and the reinforcement continue all long the leg.



the lower legs of an electra fits perfectly, but the fender is fixed differently.

and you’ll need the axel, …… also as a disk brake fork is an axel trough wheel and not an axel in wheel like the drum brake models.



this kind of kit is not made by ar host, put are a straight import from india.

hence why the don’t have the part separately.

If you wanted a set of forks that take the disk brake AND the traditional mudguard, a set for the pre-2012 C5 and early B5 models (threaded stanchion tops, leading axle sliders) will screw straight into earlier headlamp casquettes or RE alloy top yokes. As these were designed for use with the EFI wheels nothing should foul them.



The pricol caliper bolts onto the l/h slider directly, no adapter bracket required. The sliders seem to have been beefed up compared to the Electra-X type and need a longer front axle.



A.

It shouldn't be THAT tight a tolerance. It's a sliding pin calliper at the end of the day which has a pretty wide tolerance. Not even the brembo 6-pots on my VFR are to within 0.1mm, they supply 0.3mm shims with those. The allowable runout on a front disc on a modern sportsbike with opposed callipers is usually 0.2mm.



Anyway, it doesn't need to be perfectly straight and paralell, if I shim it to close enough straight and central, the sliding pins and piston float will do the rest. What I need is for the pads to be sitting directly over the disc.



The wheel already has an axle and is fitted in the bike.







I've heard a lot of arguments about how these lugs aren't designed to hold a calliper but then I considered the following. All the torsional braking force on a drum brake bullet is transmitted through the little rectangular casting on the bottom of the fork leg (which I just sawed off) via the slot in the drum. It is acting in shear which aluminium isn't great at. With a disc, the braking force is acting against the back of the fork leg which is acting in compression. All the lugs themselves are doing is holding the calliper in place in space, they will be seeing very little in the way of load. I'm also going to be bolting a bit of 6mm thick S275 steel plate firmly to said lugs which should have a significant bracing effect.

alignment of the caliper to the disk has nothing to do with what i told.



but rather the alignment of the caliper to the lower leg.

your also comparing a modern day motorcycles with strickt manufacturing tolerances, to a bullet which has not much of this.

and a part thas was not ment to serve this purpouse.



i just hope dont have a non visual casting fault in on of the lugs like i have encounterd.



the two lugs need to be perfectly straight(on both axes) or the caliper will bind!!, the floating part of the caliper has also nothing to do with picking up misalignment.

it will simply not do this.

the floating part serves only the function of braking by itself, as it has two side by side pistons it needs to float or it simply is unable to move.

So you're saying you've seen one of these things fail?



I still don't see why any misalignment can't be easily fettled out. The sliding pins will allow a good few mm of horizontal tolerance (distance of calliper from fork leg) beyond what is set with spacers because the calliper is free to float on its pins in that axis. Any rotational misalignment in the short axis (caused by a difference in distance from the disc between the top and bottom lug) can be taken out by shims. Any rotation in the long axis (caused by a failure of the lugs to be parallel with the disc) would require filing of the lugs and/or bracket to compensate. None of which seem particularly hard.



Anyway, I just found a good plan view picture of a bracket so I can work out the relative hole centres now. Cheers.