Warped discs

[Ori1234]

My MV failed its MOT test this morning, as the tester claims that the discs are warped.

When using very light pressure at low speeds (below 10 mph), I can feel a gentle pulsing through the lever. When using anything more than very light pressure I feel absolutely nothing. It has been consistent since I bought the bike (3 years now), and has never worsened or felt dangerous in any way. The pulsing in the lever at low speeds is always light.

I am convinced they are not warped (surely the pulsing would get much worse the more pressure I use?), but this is not something I've experienced before. Has anyone had something similar and been able to sand the discs down? Or is it best to replace the rotors?

[Cylon2007]

As you apply more pressure to the brakes this will actually help to bring the discs back into the middle. Easiest way to check is to get a pointer (pen,pencil, long bolt) and hold it against the fork so that it just touches the disc then rotate the wheel slowly. The pointer should maintain the contact with the disc, any warp will be easily seen.

[Steve Bass]

Very simple to test.

Set up a dial gauge and measure the run out

Or remove the discs and check on a flat surface

[Birky_41]

Out of curiosity what year and model is the MV

[Ori1234]

Thanks, I'll see if I can measure it.

It's a 2010 F4.

[moto_traxport]

These people (or similar) might be worth chatting to:

http://www.motoliner.com/motorcycle-brake-disc-str...

[TypeR]

I had similar on my Guzzi. This disc is floating on bobbins which allow it to "float". Gently tap the circumference of the disc with a soft faced hammer and you'll see the disc move slightly. By doing this a few times, you might get the disc to resit it'self on the bobbins.
If that doesn't do it, follow this guide. https://www.youtube.com/watch?v=k7TFqwoRKQE
Good luck.

[scorcher]

Most of my 990 KTM’s have had this problem. Very slight run out which you only feel on gentle braking below 20 mph. Mentioned a couple times on mots but never failed.

[roboxm3]

I had the pulsing sensation at the lever and the wheel didn’t spin too well when on the paddock stand.

I freed my bobbins using the nut & bolt method and now the pulsing is gone and the wheel spins much more freely.

Make of that what you will...

[Jazoli]

anonymous said:

[redacted]

That is not true, I've had a couple of sticky bobbins on different bikes giving the symptoms of warped discs, a nut and bolt and a can of brake cleaner has sorted it on both occasions.

[wa16]

couldn't you just take it back put it on the brake test machine and let the machine tell you?

didn't the tester offer to show you?

that's what i did when i thought my discs were warped, took it to the mot test station put it on the brake tester and watched the machine tell me the answer
they weren't warped in the end

[Dog Star]

I’d try a different MOT place personally. Never heard of that being tested before.

Funnily enough the only bike I ever had warped discs on was a 2010 model F4.

[Prof Prolapse]

wa16 said:

couldn't you just take it back put it on the brake test machine and let the machine tell you?

didn't the tester offer to show you?

that's what i did when i thought my discs were warped, took it to the mot test station put it on the brake tester and watched the machine tell me the answer
they weren't warped in the end

The MOT "brake tester" is just a set of rollers isn't it?

That wouldn't tell you if your brakes are warped, just that they can meet the minimum "stopping power" (or whatever the proper term is).

[Se7enheaven]

Bobbins.
Was same on my Hyperstrada and Multistrada.
Light brake pressure. Pulsing
Hard brake pressure. Ok
Freed off bobbins. All ok at any brake pressure.