Front brake vibration on half pressure

[drix]

Hi all

I have a question on which I would appreciate a bit of guidance and experience from fellow bikers

I have noticed occasionally some brake vibration coming from the front when applying some medium pressure to the lever, not a firm braking but not a slight slowing down braking pressure either, somewhere in the middle if that makes sense. Doesn't seem to affect the braking nor the handling but I'm wondering where that vibration comes from/what causes it an how to address it. I've changed discs, pads, clean fluid and clean piston callipers etc. yet these vibrations still occur now and then.

Current setup is near to new 320mm Brembo discs & Bendix MRR pads, silver spots with braided lines and matching M/C fitted to a standard YZF750 front end.

Any ideas and suggestions for a fix?

Cheers
Adrien

[Snod Blatter]

If you can get the front wheel off the ground and spin it can you hear it scraping the pads more at one point than another?

Sounds like lightly warped discs to me (and the Brembos are known for doing it just like the Yamaha stuff if they're 10 bobbin) but it's strange it'd be the same twice. Maybe the hub of the wheel is slightly out? Or the surface the disc sits on isn't quite flat?

[Stu99]

To eliminate simple causes first, have you also checked your wheel bearings?

[M.V.]

Yep, check the simple stuff first. If they are wave rotors (probably regular rotors also), you also need to offset the carriers.

Point 3 here: http://www.galferusa.com/motorcycle-bra ... ance-tips/

[drix]

There is a little pad drag, I get 1.5 turn when turning the wheel by hand and can’t really notice any hard points so that seems ok to me. If the discs were warped, I would have this same feel at each braking regardless of pressure?

Wheel bearings are new and the same symptoms were occurring with the previous bearings so that’s one other source ruled out. Also swapped spindle and spacer, still the same. Wheel has also been freshly balanced by my mech and the bike went through an MOT last month with no advisories.

So that’s why I’m getting lost for ideas on the subject

[cobbadiggabuddyblooo]

May just be a piston sticking every now and then.
All pistons will push once you get a bit more pressure behind them.

You have 8 pistons in all and blue and silver spots use the same sort of pistons and I'll wager when you start to apply slight pressure there will be a couple that will move first having slightly less friction to battle against.

For example if it is just 1 of the front pistons that is moving first, this may start a small flutter of the pad until the rear piston catches up with more pressure.
The flutter from the pad would push the rear piston back in too a tad as it taps against it in its rhythmic dance.
Harmonics may have some play here too.

[cobbadiggabuddyblooo]

One of the advantages of fully floating over semi floating disc is you have a little movement of the disc itself upon the bobbin to eleviate drag.

[Stu99]

Good points from MV and Cobba.
Along the lines of Cobba's comments, you could also try chamfering the edges of your pad material to assist in it's transition on and of the rotor.

[Snod Blatter]

If the discs were warped, I would have this same feel at each braking regardless of pressure?

When my cheapo Kagizumes were warped they were okay at light pressure and when braking hard, possibly because there was enough force to moved the disc around the semi floating bobbins. It was only at moderate force when the real vibration started.

That said, if you can spin the wheel 1.5 turns without any particular tight spot (and it doesn't always stop in the same place!) then maybe you're okay. But then if you can only spin it 1.5 turns max then the brakes are sticking on which can warp discs where a part of the disc cools differently with the pads making contact.

My situation was much improved with a brake refurb for reasons I still don't really understand, maybe give that a go?

[drix]

I guess Cobba has a good point there about pistons pushing out unevenly! I guess it means I get one of those tools to remove the spots, get the pistons fully out of the callipers and do a thorough cleaning? The chamfering of the pads will get done at the same time as the calliper refurb.

[M.V.]

You can remove the pistons without removing the 'Spot' inserts, no need for the special tool. But yeah, use some clean fluid or brake specific rubber grease when reinstalling, Bluespot pistons you can polish, but Gold & Silver spot pistons are coated alloy - don't use anything abrasive on those.

[fung]

Another thing to consider is unevenly tight bobbins with brake dust residue as a contributer.
topic came up in another forum.
fix is to use a bolt of suitable diameter thru the bobbin with a flat washer either side and a nut to tighten.
use a low torque setting and evenly apply tightening to all bobbins.
residue will fall out bobbins will be uniformly tight.
havent tried it myself tho.
on the list.

[Snod Blatter]

A well known trick that but you can't do it to the OE discs because there's no central hole to the bobbin, which is a bugger. It didn't save my Kagizumes either, just wore out the shims/washers until they broke up and fell out!