brake discs - how "loose" should they be?

[Geordie Mick]

Not been on here for a while for various reasons, but hoping organs collective wisdom can help me out!

Had to replace the front discs on my SV which runs a GSXR front end as one (maybe both) was warped. Can't afford to keep chucking new discs at it, so bought a used set of GSXR ones.

One is very loose and rattly. If I hold the carrier (bit you bolt to the wheel), the disc itself moves at least 1mm (probably more) in all directions around the buttons/pins (whatever they're called).

Seems a lot to me, but wondered if anyone has experience of similar?

Mick..

[Bibio]

they should flex but not rattle. the button should have crinkle washers under the washer at the back.

top tip: https://www.youtube.com/watch?v=1qoPqN2GBdw

[wideguy]

One of my racing buddies had discs on his TZ250 that had no wave washers in the buttons at all, which was annoying if you rode to the track with him in his van as the rotors rattled all the time. They did their job in stopping the bike though.
What you shouldn't have is too much clearance between the pins and buttons that would allow the rotors to move radially.

[Bibio]

thats due to them being fully floating.

[garynortheast]

That's a handy little video there Lance. Never really thought about doing that before.

[Geordie Mick]

Well, I've definitely got movement in all sorts of directions. The buttons rotate real easily. I only noticed it when I was refitting the wheel - pushing the calipers over the discs was what made me notice it.

I'll pop out and have a close look for evidence of the washers. Usual story - hoping they're ok as can't be faffed trying to sort a refund etc!

Mick..

[wideguy]

thats due to them being fully floating.
Indeed. Nothing wrong with fully floating except they are noisy and the rattling around wears out the pins quicker I expect.

[Bibio]

only problem over here is that most MOT inspectors dont like them and will fail them.

i recently got some serviceable buttons that i can chop and change between the two if i wanted.

[Geordie Mick]

Well, I've took them off and intend to take them to my local, tame mechanic for a second opinion. My money says he laughs out loud and tosses them in a skip, but we'll see...

Mick..

[PhilSV]

Mick, snap !! Gixer front end on the track bike, and discs are as yours, pad wears even and she stops well so its staying like that !! Cadwell Friday Yehaaaar !

[Bibio]

i had what i thought was a warped disc recently. i was getting a pulse while coming to a slow stop. turns out the discs were not sitting on the hubs right.

make sure that your hub surfaces are clean (dont take a file to them) just clean them up with a wire brush getting right into the inside groove.

spin the discs on the hub a few times before bolting them up

make sure that you stagger the two discs to each other e.g. dont line the bobbins up. if you line the bobbins up you get a very slight rattle out them but no pulsing on the lever.

make sure that your wheel bearings are in good order.

[Geordie Mick]

I wondered about the discs being mounted badly, Lance. The ones I think are warped are aftermarket ones (Armstrong) and were put on new. My local garage reckons they're garbage as a matter of principle, but who knows. Had it MOT'd and you could see the pulsing on the machine they use to test the brakes. Seemed quite severe.

Hub looks good and clean, and bearings are new (well under 1000 miles). The rattly ones are OEM Suzuki, but bought used. Concern is there's lots of movement in the disc itself once the pads have gripped before the bobbin takes up the slack, so to speak.

Second opinion Saturday....

Mick..

[Geordie Mick]

So, my tame mechanic's official take is they're knackered on account if the alloy carrier being worn. However, he also said that the braking surface of the disc was in good nick, and that if they're straight then he'd use them.

The MOT guy laughed as predicted but conceded he would have to pass it so.... Only one way to find out if they're straight. If it stops raining....

Mick..

[wideguy]

If your discs are warped, they'll pulse whether it's wet or dry.
If you could buy new carriers and buttons, you could certainly use flat discs, but slamming the Al carrier back and forth on the steel buttons will accelerate the wear.

[Geordie Mick]

Oh yeah, sure they will. I just meant I couldn't be bothered to get geared up to go out in the rain to test them (it is Scottish rain, after all).

I agree re accelerating the wear. However it's only used on the road, not used very frequently and doesn't get too much of a hammering so shouldn't get worse too quickly.

Mick..

[PhilSV]

Bum, took my wheels to HMT to have new rubber on them and asked Mark what he thought of the movement on my bobbins and he said that yes it was time for a change, one disc had very little movement the other was quite rattly , oh well !