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Brake disc refinishing.


mattycoops43
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Hi there


Don't know if this is possible. I have now tried 3 sets of discs on my firestorm and not found one straight set. Piece of advice for anyone, DON'T even bother trying to buy second hand discs. I had a warped disc on the bike when I got it, was sold a set that were 'perfect' for £50. I even rang the bloke to get history, he said they were on a bike he was riding, then took off the road to break, they were mint and the bike was in mot. result 40% brake force fluctuation.


Next, was kindly GIVEN a set of vfr400 discs (same fitting) by a guy on the storm forum, he posted them to me, said he thought they were ok, but couldn't be sure, very kind of him anyway! result, 25% brake force fluctuation. Frustration is mot guy said if they were 20% he would have let it go.


I think a lot of old bikes are going to have this issue, as all new mot stations have a rolling road brake tester that is mega sensitive, have been told by a local mechanic the sales staff hate it as they go to put a used bike on sale and without fail they have to fit new discs as old discs just won't go through.


£300 a set! not a cheap hobby and I can see a lot of old bikes being scrapped for it.


SO, I have 3 sets of discs, all full thickness, good overall condition, just not completely straight, we're talking probably 0.1 or 0.2 mm variation, that MUST be able to be ground down? Does anyone know a company that will refinish them for me? There's got to be a market for it!


If not, Might have to invest in a lathe and some tools for mounting brake discs!

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There is loads of guy's about and there is some that can straighten them out too


Have you checked your wheel and the hub to make sure that's fine first?


Also get them all checked and pick the best ones you may just have 3 discs out and not 6 ;-)

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matty. do you have access t a mate witht he same bike? if so, borrow his discs for the MOT.


if his disks fail the mot too then it might add more weight to the ida that your bike might be the cause, not to disks.


has your bike ever been crashed? bent wheel spindle or flattened bearings could cause similar symptoms to warped disks

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Thanks Mart


My neighbour has a few blades, we think the whole wheel might swap over tbh, but obv I want to sort my bike out properly.


Good call on checking the rest, the bike WAS front ended when I got it, the forks and yoke was bent, and I have rebuilt all that.


The only thing is there are no vibes, no pulsing through the lever, the bike rides fine, is smooth and brakes fine, the only issue is when you slow to a stop there is feeling that one half of the disc or discs is grippier than the other half if that makes sense, also the discs I mot'd it with last week showed a 40% fluctuation, and the ones I changed to were almost in tolerance, but not quite.


So, I definitely think you might have a point, but wouldn't a bent axle or dodgy wheel show up as vibes etc at high speed? I have looked down when riding and the wheel looks perfectly true, not buckled.


What would I check for? buckled wheel, bent axle, damaged wheel bearings? anything else?

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Check the disc/hub mating surface for corrosion. Disc tolerance is usually upto 0.3mm and therefore shouldn't fail a brake test. It is usually the carrier that warps not the disc so refinishing wouldn't work.


ST Motorcycles at Foston can retrue discs, £50/pair typically.

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I agree about the rolling road being mega sensitive, I sometimes went to Roy Hanks of IOM TT sidecar fame for MOT's & he uses a winch with a strain dial while you sit on the bike, some distance for you Matty but if there's a similar tester around your area,,,

https://plus.google.com/116967014887117 ... l=uk&hl=en

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I agree about the rolling road being mega sensitive, I sometimes went to Roy Hanks of IOM TT sidecar fame for MOT's & he uses a winch with a strain dial while you sit on the bike, some distance for you Matty but if there's a similar tester around your area,,,

https://plus.google.com/116967014887117 ... l=uk&hl=en

 

I used to love watching the Hanks brothers at Cadwell....they were bloody mad but amazing riders...

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Theres a process where basically a lathe grinds them down to being straight and flat. Saw it on wheeler dealers so must be doable!


As long as it stays above the correct thickness it is all right!

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Try freeing off the bobbins and then try em again on the tester. :mrgreen:

:stupid:

I've had disks where some of the bobbins have seized. Check the ones that just failed matt. Could save you a fair bit of money mate...... :wink:

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Thanks guys, I checked the bobbins, there was a bit of dirt behind but not a lot and they were moving freely. I know it can be the carrier that warps, going to check everything else is straight, then send them off for straightening.

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Thanks for the link Bob, looks good, mine are the same as cbr 900, 600, vfr 400, vfr 750 etc etc etc form the 90s they all used the same disk, so the ones listed would be ok for my bike.


I have been advised to stay away from cheapie replicas, but tbh, any comp[any that manufactures their own to sell I am interested in because they have control of their own quality control and any issues you can go back to them direct.

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Thanks for the link Bob, looks good, mine are the same as cbr 900, 600, vfr 400, vfr 750 etc etc etc form the 90s they all used the same disk, so the ones listed would be ok for my bike.


I have been advised to stay away from cheapie replicas, but tbh, any comp[any that manufactures their own to sell I am interested in because they have control of their own quality control and any issues you can go back to them direct.

And reading the blurb on their page it seems like they are not using cheap materials in the production.....and as you say they are UK based, so you can contact them directly if you have a problem.......but they responded pretty quickly when I had a question for them.....so I think they are pretty legit..... 8-)

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