MK3 Disk Brake Machining / Grinding Queensland Australia

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Discs are chrome plated cast iron, not stainless.
I turned the chrome off the discs with a lathe years ago. The surface of a cast iron disc is much better than chrome or stainless for that matter.

Stainless and chrome plated disc are used because they don't rust.

Norton disc were the same size as used on some BMC Mini's and they weren't plated.

Grinding or turning the chrome off your disc will improve the performance of the brakes. Once the chrome is removed spray alittle hi temp paint on the surfaces where the pads don't touch.

I reduced the bore size of the master cylinder, removed the chrome from the disc's and use EBC brake pads. No, it doesn't stop like a new bike but it is much better.
 
If you live in a wet climate, zinc plating will reduce the rust and is not as slippery as chrome.
 
I think you will find that the Commando disc is cast steel not cast iron. Two entirely different materials. You would struggle to chrome plate cast iron due to the "free carbon" that is present.
 
Not so - when I drilled my Commando disk, the drillings came out as short grey flakes.
Sure sign of cast iron.

I have a number of plated cast iron objects - mostly nickel plated, but several have then been chromed.
Excellent plating...
 
Thanks Guys,

Thanks for all the replies, i'm wondering then if they are not Stainless Steel and infact Cast Iron why a normal
car brake place cant do them, must be something to that as everyone says they need to Blanchard Ground.

The idea of getting an engine recondition place to do them is a good one, imagine they have the tools to grind heads and such
so should be able to do disks, will look into that today.

I tried one disk yesterday in 100% Hydrochloric acid for a few hours checking every half hour or so and it didn't successfully get all the chrome off either.

Both My master Cylinders are being rebuilt at the moment and having the front modified with the smaller piston and replacing all lines with Braided Lines
as I am more for function than originality and my old lines are toast

Hey Mr.Sparks do you have any contact details? I tried searching gfh150 on ebay and couldn't find anything? guess if this Person is in US by the time i stuff around im
probably better buying new disks.........

new OEM seem to run me about $295 AU Each Delivered. I love the look of the drilled and lightened Old Britts ones $460 AU Each without
shipping tho!!
 
So I just had a thought,

I've rang around a few places and got some funny questions when I ask about Blanchard Grinding, but I remember
I had to get a flywheel machined a while back for another project and they said they couldn't do it on the laith
either, quick youtube and it looks like the grinding machine they use to do Flywheels looks like it would work
perfect on brake disks :)

Rang a clutch place and they reckon they have this surface grinder and it should work, gunna drop in today and see
what they think.
 
CHARGER said:
Thanks for all the replies, i'm wondering then if they are not Stainless Steel and infact Cast Iron why a normal
car brake place cant do them, must be something to that as everyone says they need to Blanchard Ground.
Click to expand...

It sounds like someone looked at the chrome on that disk, and just assumed it was stainless. (?).

I just polished my (rusty) disk clean with an orbital sander - but most of the chrome was gone by then.
Your clutch place seems like a good idea.
Don't let them take too much off.

Doing it on a lathe doesn't get it real smooth - which removes quite a % of the braking surface area.
Its not easy to take a fine cut off a cast iron surface.
If the tool chatters at all, even worse.
Grinding it makes a perfect (flat) surface.
 
So turns out I should of gone to this guy first :)

$60 each disk, even bead blasted the centres for me, done in 2Hrs!
They used the top surface where the disk bolts on as a Flat reference so to speak
then ground the underneath then the top

MK3 Disk Brake Machining / Grinding Queensland Australia
 
Gold Coast Brakes and Clutch

Unit 7, 28 Expo Court, Ashmore, QLD 4214
0755323555

I didn't ask actually, he may well do
 
If those guys did a real good job then you are in luck. The problem with machining one side at a time is that you are relying on the precision of the machine to get the thickness exactly even all the way around. Disk brakes are super sensitive to variations in the thickness of the disk. All your disk brake machines cut both sides at the same time with the main dimension absolutely held steady being the thickness. (i.e. how far apart the cutters are from each other.) You might want to measure the thickness with a micrometer before bolting it on. If it is more than .001 inches out you'll have a problem.

It looks really great though!!
Dan.
 
Hi,

Your results look good. I too when this way (cost 60€) but afterwards the disc was too thin. The Workshop manul quotes thiickness to be "Disc width at frinction area 0.026/0.025 in (6.604/6.35mm)

Ended up buying a good used disc for 42 GBP.

Regards,
Sean
 
What Workshop Manual quotes this,
and what page number. ?

BTW, Not sure I'd believe that, it sounds about the thickness of aluminium cooking foil !!
The Imperial measurements anyway.
Cheers !

A BM disk here has a nominal thickness of 7.0 mm, and it says on the carrier "Min Thickness 6.3 mm".
Thats a 0.7mm wear limit, or approx 28 thou.
A Guzzi cast iron brake disk quotes something similar, but i don't recall offhand what the precise numbers are.
It has previously been discussed here that Nortons don't seem to have quoted a wear limit for the disk, at all.
Which is a trifle offputting, since there has to be one...
 
Hi Charger,
My local engineer lathed my discs perfectly flat and true making a boss to hold discs in his lathe, which I have for future use. The result was shudder free action as discs were up to 32 thou out.
If you want to send them down south to VIC I could have him lathe then for you.
Cheers, Vintner
 
Hi,

Sorry there was a typo with the imperial figures. Should have been 0.250/0.260. Metric was correct.

Anyway, 850 mk 3 Publication number 00-4224 no page number just section A - Technical data.

Regards,
Sean
 
vintner said:
Hi Charger,
My local engineer lathed my discs perfectly flat and true making a boss to hold discs in his lathe, which I have for future use. The result was shudder free action as discs were up to 32 thou out.
If you want to send them down south to VIC I could have him lathe then for you.
Cheers, Vintner
Click to expand...

Thanks vintner,

I'll see how these go, still a little while before she's on the road
 
I get my disc's done by Gary Hollowich in the US, have had two pairs done, they really do come up nice.
 
If you've got a $20 head, wear a $20 helmet. You guys are talking about drilling discs when you don't even know what the material is. There are people about making very nice aftermarket discs, buy yourselves a pair. My bike is fitted on the front with a pair of relatively small diameter Suzuki discs and two AP calipers. They work extremely well. I believe the disc material is high speed steel - I still would not drill them for lightness. A friend was killed at Bathurst in about 1977 when the discs exploded off his RG500 -replaced with the wrong material (cast iron) because the chrome spalled off the originals. Take care, you are not playing tiddly-winks !
 
High speed steel? :roll: . Do you know what HSS is ...think drills and lathe tools. :!:


acotrel said:
If you've got a $20 head, wear a $20 helmet. You guys are talking about drilling discs when you don't even know what the material is. There are people about making very nice aftermarket discs, buy yourselves a pair. My bike is fitted on the front with a pair of relatively small diameter Suzuki discs and two AP calipers. They work extremely well. I believe the disc material is high speed steel - I still would not drill them for lightness. A friend was killed at Bathurst in about 1977 when the discs exploded off his RG500 -replaced with the wrong material (cast iron) because the chrome spalled off the originals. Take care, you are not playing tiddly-winks !
Click to expand...
 
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