Loose brake disc?

[Fladdem]

Hi, currently I'm throwing money at a bike that isn't worth it. I noticed the other day that the front disc is kind of loose. When you stick the front brake on the rim continues to rotate a bit, it's a little bit unnerving, and I don't think the back does it. They are Avid BB5's, in case that makes a difference. I am thinking that it's something to do with moments, i.e. the length of the spokes to the rim act as a lever about the disc as the pivot and the wheels momentum? I don't know though because I don't think the back does it, or if it does it isn't noticeable, and the front does it just at a standstill, just rocking the bike.
Any help would be appreciated,
Adam
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Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[KLR600]

Erm, just tighten the disc bolts?
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Now: '00 Kawasaki ZRX1100R - Past: '84 Yamaha DT125, '89 Kawasaki KLR600, '97 Yamaha XJ600N
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[Fladdem]

They are, I forgot to mention that. I don't know what's causing it. I didn't mean loose just wobbly.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[G]

Is the hub definitely moving?

It's not unusual for there to be a bit of play in the spokes in such situations.

[Fladdem]

I had a look today and I noticed a load of loose spokes, I went round to try and re tension them and the problem seems to have got less, the rim still moves a smidge round but it's more sturdy. It still does it though just not as much. I guess I'll live with it, I have done for ages. I was mostly just wondering if it was a universal thing, if all discs did it or maybe its flexing spokes or something, it still has me puzzled but there seems to be less movement.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[KLR600]

It could be any number of things as there's plenty of things on the front end of a bike that could cause a little bit of movement if worn out/loose. If it's bothering you to the point of really wanting to do something about it then I'd set an afternoon aside and go through the front end thoroughly from top to bottom.

Hard to pin it down without seeing it and I suppose it's quite difficult to describe where a small movement could be coming from on the front end.
____________________
Now: '00 Kawasaki ZRX1100R - Past: '84 Yamaha DT125, '89 Kawasaki KLR600, '97 Yamaha XJ600N
<My Bikepics Page> <My Yootoobes> <My Websites> <My Photos>
<Take Cool Photos!>

[Fladdem]

I swapped the wheel out with a new wheel I had knocking about in my garage. The wobbling was still there, just less, I think it may be the fork tubes moving in the suspension, that may contribute something to the wobbliness, but I think the original wheel needs examining thoroughly. I'll check everything on it like you say, just work through everything. I can live with it but now that I have noticed it I can't stop noticing. Like when someone points outs that your handlebars are bent before you spotted it and then it's all you can think about.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[stinkwheel]

I presume the wheel is conventionally spoked with leading and trailing spokes (ie every spoke crosses three other spokes)?.

Radial spoking and a disc brake would cause all manner of problems.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Fladdem]

Yes, normally spoked. I don't disbelieve you but why would radial spoking cause problems? Would the rim continue rotating a lot and bend the spokes or collapse the wheel?

I am not sure, but is there like a rubber grommet or something maybe that goes in the disc, probably not, but I was just wondering if maybe there was a damper that might have rotted, I'm clutching at straws now. I've never had a disc rotor off, never even had disc brakes until a few months go, always used to use rim brakes.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[joef]

Are you sure this isn't just the pads moving in the caliper? Get someone else to move it while you have a look. The pads will usually move a small amount with the brake held on.

[Fladdem]

Thats a very good suggestion. I shall check it out tomorrow! My bikes are all a bit wrecked, I buy on a whim, always second hand, and can never say no regardless of condition.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.