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Brake discs
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Sun Feb 08, 2015 12:15 pm    Post subject: Brake discs Reply with quote

Hello..anybody had any success getting brake discs manufactured,just a pair, not a job lot. Looks like the discs for my Armstrong Siddeley Star Sapphire are unique. The calipers are same as Rover P5 but apparently the offset is different for the discs.

On the subjsect of which....what kind of steel is needed for discs? Never thought about it before?

G
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Sun Feb 08, 2015 4:49 pm    Post subject: Reply with quote

Shouldn't be too difficult to machine from a solid piece, but quite a lot of wastage. I have seen discs of stainless, but as most rust, I assume they are made of mild steel.
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KA

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Kenham



Joined: 12 Mar 2012
Posts: 209
Location: Kent

PostPosted: Sun Feb 08, 2015 5:28 pm    Post subject: Reply with quote

All the ones I have skimmed have been cast iron , same material as a brake drum I presume. I think I have seen a couple of firms advertising disc manufacture one offs, not sure where though or how much. Ken
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Sun Feb 08, 2015 8:50 pm    Post subject: Reply with quote

Cast iron is the usual material. Whatever you do, don't go for stainless steel. In the early days of disc brakes on motorcycles they were mostly stainless, but SS is hydrophilic (ie. has an affinity for water), so in wet conditions a microscopic film of water would adhere to the disc and prevent the pads from reaching the SS surface for several revolutions after the brake was applied. In essence, the pads were aquaplaning. Not the sort of excitement most of us want—indeed, it was bl**dy dangerous. Manufacturers tried all sorts of remedies such as drilling holes in the discs, which had no more effect than making them more expensive and look pretty. I believe the problem was finally overcome by the use of sintered disc pads.

Richard
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ajb100



Joined: 30 Jan 2015
Posts: 16
Location: Chippenham, Wiltshire

PostPosted: Sun Feb 08, 2015 9:36 pm    Post subject: Reply with quote

As said, they will be cast iron. Can you find a disc with a lower offset that you could then space off the hub to centre them in the caliper. This would only work if you could get them within ~5mm as it will obviously affect wheel track width and stud length.

Alternatively, I've used Apec in Yate in the past when designing a new brake set up for out single seaters. They have a huge range of options, although ours were just rotors, they did did traditional dicas too
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Mon Feb 09, 2015 7:51 am    Post subject: Reply with quote

I accept they are cast iron, the cheapest and most costs effective way of mass production, but would mild steel do?
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KA

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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Mon Feb 09, 2015 9:49 am    Post subject: Reply with quote

Well the basic difference between cast iron and steel is the amount of carbon content. This probably has a small affect on friction and durability?

I'd imaging there won't be a huge difference in performance, and that the material of choice is down to manufacturing; for high volume cast iron with minimal machining would be the most cost effective, for low volume mild steel with more machining, so the unit cost would be higher , but cheaper than a small run of castings.

My aftermarket MGA discs are mild steel and work fine with standard pads.

Dave
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MikeEdwards



Joined: 25 May 2011
Posts: 2464
Location: South Cheshire

PostPosted: Mon Feb 09, 2015 11:48 am    Post subject: Reply with quote

I was talking to a chap at a company called Nitrac Ltd (Macclesfield way, though the workshop is in Cambridge area) about getting some replacement discs for my car, which are also quite unusual. His plan was for me to provide some measurements and he would then see whether a standard off-the-shelf disc in their catalogue could be machined down to suit my car.

As it happened, the dimensions of mine made it unsuitable for this, but it might be possible for yours.
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Mon Feb 09, 2015 6:47 pm    Post subject: Reply with quote

All interesting stuff.

I just know that on the few occasions when I've gone to get something machined, I invariably end up talking to a chap in a brown store coat looking at me like I'm a comlpete idiot and saying something like
" Good god NO! You don't want that made up in bright mild , you need a low carbon mild with 2% butter and 0.5% bat's urine"

I think I'll call those guys in Macclesfield, see what they say. That sounds like an option.

Totally get the point about SS discs. I had a Suzuki GSX1100 once, bloody great big heavy thing with a motor like a turbine, fast as a fast thing, terrible handling and shocking brakes. Despite twin discs and uprating the calipers it never really stopped properly. Curiously, at about the same time I got a damaged BMW R80 from an auction for chip money, it had a single disc with a single pot sliding caliper!! However, I replaced the knackered disc with an aftermarket cast iron one, which looked dreadful in the morning, it'd rust overnight..BUT...by god that bike stopped just fine!!!!
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ajb100



Joined: 30 Jan 2015
Posts: 16
Location: Chippenham, Wiltshire

PostPosted: Mon Feb 09, 2015 9:34 pm    Post subject: Reply with quote

There would be no real reason you couldn't use mild steel but there would be many draw backs from it compared to cast iron

Probably the most obvious being wear. Being much softer than cast iron, they will never last any where near as long

You could try going for a high carbon steel, but then machining costs will start to rocket due to specialist tooling needed. Carbon steel will also suffer from the heat becoming harder and harder and developing surface cracks
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Tue Feb 10, 2015 8:04 am    Post subject: Reply with quote

Back in the bad/good old days when we used asbestos in brake pads, I used to replace just pads at the garage, now I replace pads and discs at the same time.
Does this logic seem to be that pads are harder?
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Tue Feb 10, 2015 8:40 am    Post subject: Reply with quote

I had a BMW 6 series from new, traded in last year, with 75,000 miles on the clock it still had the original discs and pads on all 4 corners admittedly a good chunk of the milage was motorway, but still surprised me Shocked

Dave
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Tue Feb 10, 2015 4:23 pm    Post subject: Reply with quote

ka wrote:
Back in the bad/good old days when we used asbestos in brake pads, I used to replace just pads at the garage, now I replace pads and discs at the same time.
Does this logic seem to be that pads are harder?

Yes. Pads nowadays have a high metallic content, sometimes referred to as sintered. The cheaper types also make a foul mess of excessive dust, particularly noticeable with alloy wheels.

ukdave2002 wrote:
I had a BMW 6 series from new, traded in last year, with 75,000 miles on the clock it still had the original discs and pads on all 4 corners admittedly a good chunk of the milage was motorway, but still surprised me Shocked
Dave


Motorway driving would help, but a lot is down to driving technique. With modern automatics people get lazy and ride the brakes all the time instead of controlling the gearbox, eg. when descending hills at slower speeds. With my previous car the WoF (MoT) inspector told me every six months for three years that the rear pads were getting thin; eventually they had to be changed just before trading it in.

Richard
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JohnDale



Joined: 19 Mar 2008
Posts: 790
Location: Kelvin Valley,Scotland

PostPosted: Sun Apr 05, 2015 4:34 pm    Post subject: Re: Brake discs Reply with quote

trampintransit wrote:
Hello..anybody had any success getting brake discs manufactured,just a pair, not a job lot. Looks like the discs for my Armstrong Siddeley Star Sapphire are unique. The calipers are same as Rover P5 but apparently the offset is different for the discs.

G


Is it not possible to use spacers on the caliper to centralize them on the disc - depends which way they need to move,cheers,JD.
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Thu Jul 02, 2015 6:49 pm    Post subject: Reply with quote

Ended up getting a local bloke to make them up from cast. One man band in a sweaty workshop full of calenders depicting sexy girls in bikinis.
Clearly the right bloke!
Just gone on the car today.... Seem the mut's nuts.... Job done.
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