MOT wear limit, floating discs/bobbins?

[OutInTheShed]

We have a small but high mileage bike, the front disc rotor has some movement on the carrier.
When pushing the bike with the brake on, it's noticeable, thought it was head bearings at first.
I can't feel significant sideways movement.
For complicated reasons, we'd like it to pass the MOT first time!
The MOT tester is on holiday so I can't ask him!

Do I just order a cheap new brake disc?

TIA.

[Stevemr]

This is from the government web site:-
1.1.14. Brake discs and drums

A brake disc or drum must be significantly worn before rejection is justified. Being worn below the manufacturer’s recommended limit is not a reason in itself.

Defect Category
(a) Brake disc or drum:

(i) significantly and obviously worn
(ii) insecure, fractured or otherwise likely to fail

Major
Dangerous
(b) Contaminated with oil, grease etc. Major
(c) Missing Dangerous
(d) Brake drum back plate insecure

So I guess it’s if the mot inspector thinks it’s significantly worn.
Probably. Pretty good idea to change it if you or any one else is going to ride the bike.

[OutInTheShed]

Yes, I saw that, I wondered if anyone could clarify 'significant' or 'obviously'.

It's not proving easy to find a new disc that I'm sure will fit.
I don't think it's going to fail in the next 10,000 miles.

It's not really much more slack than when pads move back and forth in the calipers sometimes, but it is 'noticeable' if you're looking for it.
Or if you're looking for play in the head races...

[trickywoo]

If you thought it was head bearings at first so will the tester and then when he sees that is actually the bobbins I think it will be a fail.

[catso]

Both my Ducatis have suffered significant play on the front discs, one due to worn bobbins the other worn carriers. On both occasions the MOT tester warned me but neither failed them or gave an advisory, I have since fixed both.

I think it would need to be considered dangerous to be an issue but different testers will view that differently.

[OutInTheShed]

catso said:

Both my Ducatis have suffered significant play on the front discs, one due to worn bobbins the other worn carriers. On both occasions the MOT tester warned me but neither failed them or gave an advisory, I have since fixed both.

I think it would need to be considered dangerous to be an issue but different testers will view that differently.

Possibly new bobbins are an option.

I suppose the 'danger' might not just be potentially breaking, which isn't going to happen any time soon, but also if the slack allowed the brake to judder or something, reducing effectiveness.
I might stick the wheel in the car and go find another MOT tester.

[OutInTheShed]

trickywoo said:

If you thought it was head bearings at first so will the tester and then when he sees that is actually the bobbins I think it will be a fail.

How can you say that without quantifying how much slack we are talking about?
There will be some play in a new bike, even if you need Mr Mitutoyo to measure it.

[catso]

OutInTheShed said:

Possibly new bobbins are an option.

My Monster which had steel carriers/alloy bobbins needed new bobbins, the 916 has alloy carriers/alloy bobbins and the carriers wore quite significantly (must be softer than the bobbins) which was a shame because new carriers cost significantly more than the bobbins.

[trickywoo]

OutInTheShed said:

trickywoo said:

If you thought it was head bearings at first so will the tester and then when he sees that is actually the bobbins I think it will be a fail.

How can you say that without quantifying how much slack we are talking about?
There will be some play in a new bike, even if you need Mr Mitutoyo to measure it.

You said the movement felt like head bearings. That s a fail and if it s moving that much because of play in the bobbins it s a lot of wear.

You might well pass though. The subjective nature of the mot might mean a tester passes you because they trust you or whatever. I got a pass on a car when I shouldn t because the tester felt sorry for me. I turned up to the test covered in dust and looking tired from a diy project.

[MrGman]

Ultimately this will come down to the discretion of the tester, there’s no way to tell until you get your tester look at it.

[OutInTheShed]

I've managed to find a new disc which I think (hope?!) will fit, I was going to put new pads in anyway, and the working faces of the disc show some wear.
New disc is only £22 and is solid not floating.