Drilled discs

I've seen drilled discs on several nice bikes on this site,

Do they make a big difference over the standard discs ?

Where did they come from and how much ?

My bike has a AP caliper on the standard disc but I've never ridden it so I'm unsure of it's usefulness.



Thanks for your advice

Graeme.

Here's a closer picture, is this set up any good ?

Saves some weight (3/4lb on mine) and seems better in the wet. Biggest improvement though is a smaller diameter master cylinder for more hydraulic leverage. 11mm is best for a single but 13mm works well on mine (RGM conversion). Depends what your lever to caliper piston ratio is. I heard the AP setups are not much better than std Lockheeds but someone else will comment.

Hi Graeme
I agree with Keith.
I bought the bigger disc from RGM motors, and also a Grimeca caliper, which is the same twin 43mm piston diameter as yours. I selected EBC kevlar pads. Mine felt crap in the wet though
With the standard 5/8" diameter master cylinder piston diameter it still felt 'wooden' and without 'feel'. I was very disappointed at the lack of improvement.
By far the best thing I did was select a new master cylinder unit with an 11mm diameter piston. I bought a second hand unit off a scooter, for five quid! Far cheaper than all the money spent on the disc.
This transformed the braking. I now need two fingers to operate the brake. I will try and get a photo of the unit, I also grafted the original switchgear to it.
The magic ratio is about 28:1
(43/2squared x pi) x 2 ....divide this by 11/2squared x pi....

My advice is get some good pads....do a search on this thread....get a braided hose assy and change to a smaller master cylinder diameter.....RGM do a conversion to take the standard Norton unit down to 13mm.....in my opinion 11mm is better, but 13mm will improve it. If you get the bigger dia disc you will need to get a new mounting plate for your caliper, as well. Keith seems to have a standard dia drilled disc on his...9" I think?

GRM 450 said:

Here's a closer picture, is this set up any good ?

Click to expand...

No bolt for the front fender stay hole? Looks like there is a hole on the plate behind it.

hi graeme,according to vintage brake ,norton and triumph discs should,nt be modified,but they dont explain why not but suspect it could be a safety issue

Lighter weight and faster heat dissipation are the benefits.

I've never seen anything substantial that makes any case for not drilling lockheed rotors. Someone will quickly google something to put me in my place in this tiny little world I'm in though, I'm sure of it...

Still, way more than a dozen on at least 10 bikes; better braking, zero issues...

If a disc is going to crack then it'll start at the drillings. I don't think that anyone will recommend it without knowing how careful the owner is going to be with regular checks.

Even factory drilled discs on other makes have been known to crack (BMWs spring to mind).

I suspect that the consistency of the cast iron on NVT discs is not all that it might be and there are so many old discs plus new replacements from who knows what source out there that it would be a bold supplier especially in the US who'd recommend it.

I'll parrot Chris's response from Vintage Brake. Mike Morse, Vintage Brake owner, gave a presentation during an NCNOC lunch in Angels Camp, Ca a couple of years ago. His reason not to drill a stock Norton rotor is it significantly weakens a rotor that is already prone to cracking. I think the main reason to drill these is it looks pretty. Doubt if weight savings can be of any significance to the bikes performance.

I certainly won't suppose to contradict Mercury Morse, but I have had several drilled discs, and have never had one crack. I have been careful to chamfer the holes on the ones I drilled. All of these had the chrome ground off the braking surface. The holes seemed to help keep the rust from imbedding into the pads. Of course these days, I go for the larger modern disc and 4-piston caliper! :wink:
The theory on holes from the brake manufacturers is to provide an outlet for the gas that is generated on a hot pad, keeping the pad in more direct contact with the disc. I am not certain that a stock caliper and disc can generate enough force and heat to see this effect.

As swooshdave observed there is a bolt and spacer not installed in the caliper mount. (the rest of this bike had worse problems than this)
I hadn't ridden the bike before I dismantled it for a complete rebuild, so I don't know how this caliper worked.
I understand the master cylinder to caliper ratio required, but I've seen discs fitted to bikes on this site other than standard and also calipers that look like Brembo or Nissin ?

I would be interested in the 11mm master that BigStu used, a picture or the scooter model.

I will try and post a link to a brake ratio chart that I've found useful in the past.

Regards Graeme.

Brake ratio chart, I think this is preaching to the converted but maybe some one hasn't seen it before.

www.vintagebrake.com

see ratios

I have a MKIII with OE disc, I turned the chrome off both disc and use the 13mm master cyl mod, improved brake responce 100%.

Ken G.

I think the caliper was used on an Italian or Spanish scooter, but they are popular on trails bikes.
Bultaco 250 maybe....old age and memory are a terrible thing :?
Anyway here is a picture and a link.



It is like this one but has a little brake light switch fitted......which makes it look like this one......




I will take a photo on my bike and see if there is an exact code on it. I bought it off a mate who bought it at a 'car boot sale'
JimC got one off an MZ 250. I have seen this one too.

Here is a link to an AJP site, paste it into google address bar..

http://www.ajpamerica.com/master-cylinders.html

illf8ed said:

Doubt if weight savings can be of any significance to the bikes performance.

Click to expand...

Keith1069 claims a reduction of 3/4 LB. Don't forget this is unsprung weight so that's a good thing for front end handling.

Re: Drilled discs
by ludwig » Mon Aug 24, 2009 12:26 pm

79x100 wrote:
If a disc is going to crack then it'll start at the drillings.

that's why every hole you drill should be chamfered both sides .

OOPS Ludwig I dif just that after I drilled my discs and made them floating BUT it actually made them worse in the wet .A possible reason is that the outer surface of the hole(chamfer) is bigger than the drilled hole itself so when you put pressure on the disc the pads try to put more water in the hole than it can contain and actualy stops the pads from making contact with the disc (the chamfer was a tiny one just to take the rough edges of)
I grinded the rotors to restore them but this is not possible on standard discs (mine are floaters so can be separated from their carriers) I would not drill them again because i have a very nice drilled disc on my wall with a crack all across but again these are cast iron rotors

here s a link to what i tried to explain

Made sure mine were well chamfered. I check them often and so far no problems but I am aware! 12,000 miles on this disc.

lynxnsu said:

here s a link to what i tried to explain

Click to expand...

Arn't the holes in your disc going the wrong way :?:

Yes they do in the pic .But I have fitted them in both directions in the past and can not feel any difference (even on track days)
However according to Fred Puhn-The brake handbook isbn-0-89586-232-8- they should point in the opposite direction but I do not know why Any ideas????????
ps even Ducati sometimes fitted them the other way round but that is hardly a reference as they fitted what was left in the bin and as they pleased