1200 Not Warped Disc But Feels Like It At Slow Speed Braking

I would suggest taking it to your local friendly bike mot place and ask them to put it on the brake test rollers. That way you/they can see the fluctuation in brake effort, and could check for any run-out too. 10 minutes and you can see what your trying to deal with.

 

Had a monster with the same symptoms. Tried Scottish brite and cleaning the bobbins to no avail. Dealer said run out was in spec as I watched them check it. Removed disc and rotated to a different position on wheel. This changed the vibration frequency to an acceptable level. Not perfect but much better.

 

This is a problem which is regularly reported.
Warping is often blamed, usually incorrectly.
Seized bobbins can contribute, but only slightly.

I had three consecutive mot advisories for this very issue, starting around 2008/9.
Symptoms were the usual, minor pulsing at very slow speeds which made trundling in slow traffic a nightmare but had no noticeable effect whatsoever on normal braking at speeds above walking pace.

Cutting to the chase, although I did clean the bobbins and also went over the discs with scotchbrite and later with a flat block covered with 400 grade abrasive, the improvement was minimal.
Then I did a trackday at Mallory and I used the brakes in much more anger than I usually do on the road, and over an extended period.
Riding home, the pulsing had significantly reduced.
Further hard braking on the road was therefore adopted and the end result was that I'm still running the same discs some 10yrs and 20k miles later and they're as smooth as silk.
Furthermore, there have been no other changes .. I'm still on the same pads and the calipers have seen no new seals etc, only a decent clean up (oh and titanium retainer pins, but I doubt they're relevant here).

My understanding/theory is that an interaction between the discs and the pad material results in a conditioning (sometimes misleadingly called tempering) of the surface of the disc and dictates its ultimate frictional qualities.
This can happen on two fronts, the major one being a positive effect whereby a surface deposition from pad to disc (on a near-microscopic level) results in the disc becoming much "grippier" than when brand new and unused. This seems to be a widely accepted phenomenon and happens on all new discs.
But there can also be a negative effect where this surface conditioning can later become degraded, unevenly in patches around the disc. This might occur either due to holding the brakes on after braking hard to a standstill, which creates a stationary hot spot where the pads grip while the remainder of the disc cools rapidly .. or (and here this is just my opinion, but I'm totally convinced) degredation occurs when the bike is parked up with wet pads which corrode the discs (yes they're "stainless" but the grade used for best friction has the worst corrosion resistance) and thus also "corrode" the surface conditioning.
This then results in the pulsing.

My advice would be to clean the bobbins and lightly (and evenly) abrade the discs to start with.
Then go out and use the brakes fairly hard, the aim being to recondition their surfaces by evenly redepositing a new layer of pad material. Stop occasionally if you like, but don't hold the brake on when you do and even perhaps keep the wheels moving slightly while the disc cools. I didn't go out specially to do this myself, but I guess the trackday had the same effect. It may be sufficient just to resolve to use the brakes harder for a while in general riding. The key factor is probably to avoid local hot/cold spots on the discs eg when stopping as descibed above.
Also, after a wet ride, don't leave the wheel stationary for long periods .. spin the wheel or shuffle the bike periodically.

It is interesting that Robarano reports a possible improvement after a trip to Italy.
What with the frequent hairpins and the Italian attitude, the brakes get a good workout .. and in a hot, usually dry environment too.
This would be an effective reconditioning treatment for the discs.
I wouldn't swear to it but I fancy that a trip to WDW in 2014 was possibly the final stage in the reconditioning of my own discs.

Short summary is .. clean em up (optional.ish) then use them harder .. they'll come back to you .. and for free.

ps. when its really hot (or anytime really) if I stop at traffic lights etc where more than a short wait is anticipated, I often leave the bike in neutral and kill the motor.
Then the brakes can be released and the bike will hold its position against the drive train.
In addition to protecting the brakes, this also keeps the engine cool as well as reducing emissions.

 

Having exactly the same problem and, having just fitted M50 calipers & pads, I can safely say it's disc related. As soon as the ice clears, I'll get out and take a run up to Oban, braking like a loon ;-) - Your point is good, given that both JohnW and I are IAM gits and therefore tend not to work the brakes much on the road, if at all.

 

Lots of the steps here are recommended, I'll add a couple that worked for me...
- free up and clean the bobbins as mentioned
- go over the rotors with a Scottish brite pad to remove deposits
- with light sandpaper sand the braking surface of the pads. If they squeeked, file a chamfer on the leading and trailing edges.
- now bed in the fresh surfaces by doing 10-15 hard stops from ~100kph to ~10kph. Don't stop fully. Ride a mile or two to cool, then do it again for 3 or 4 times.

IMO the last step is what most owners don't do either after buying a new bike or new brakes which results in uneven deposits and pulsing. On mine I had to do this about once per year because the pulsing returned. After switching to HH sintered pads and repeating these steps I've never had the issue since

Cheers

 

Have the same problem on my Hypermotard; it even failed the MOT once for "warped discs" and the MOT tester laughed when I said that I'd be back in an hour...

Take your calipers off, take the pads out and clean the calipers. The monoblocs are dreadful at trapping dirt which causes the pistons to stick and produce the feeling of warped disks. I usually clean mine with plenty of brake cleaner and the wife's toothbrush, then reapply some coppaslip to the pistons and make sure you give them a good pumping not only to free them off but also before you take it out for a ride.

Wiped the smug look off the MOT tester's face when I went back and my disks were no longer warped...

 

Thats true when cruising Richard (IAM Advanced pace), but when pressing on (aka 'Ave it' pace) especially when fully loaded, my brakes get used a fair amount (working on the old adage: if you didn't need to brake for the bend you weren't going fast enough for long enough down the straight )
My rear disk is blue

Working them hard will help to clean them, but giving them a good going over with a scotchbrite wheel will help better imo.
If you can get the bike on the centre stand and a helper to hold the rear down you should be able to spin the front wheel with the brake lightly applied to find/feel the grippy / less grippy patches.
On mine the patches are visible once you know what to look for.

@antonye thats a great tip too. I think a lot of people forget to clean the calipers. Doesnt your wife complain about the taste of her tooth paste ?

 

That's interesting.
Can you describe their appearance at all ?
Is there anything in their appearance that mimics the shape of the pads' contact area ?
The reason I ask is that I'm looking for evidence to support my theory that surface degradation of the discs occurs when the pads are stationary, either against a hot disc or when they are parked up and left when wet.

 

That happens on cars a lot when parked a while. It is the disc that rusts slightly all over apart from where the pad is on the disc. Then when moved you can see a patch on the disc. Wet or damp discs rust. Bet most of you have a nice dry garage though so that should not happen.

 

utopia, the best I can describe is it looks glazed / polished in some areas, and pitted in others. No, its not specific to a pad shape as such. If it were, that is likely to be pad material migration (sticking to the disc). When you get off your bike have a touch of the discs to see if they are hot at all. Usually mine are not as they get chance to cool down before I stop, unless of course I stop mid-thrash for a pee/photo stop.

Stevie, I know what you mean. Putting a car away after its been driven hard and the brakes not allowed to cool can actually cause pad material to bond to the disc. This is what makes it feel like the brakes are on when you then go to pull away the next time. This usually clears off after a few goes on the brakes though. I've experienced this a lot with cars that have iron discs, but not on any of my bikes.

 

Just a tip -
I now know when my front discs need a clean, the bike groans when I wheel it out of the garage, I'm sure you know the noise . To clean the discs I now use Methylated Sprits on some kitchen towel and wipe the discs over when cold, the meths evaporates very quickly and leaves no residue and is cheaper than Brake Cleaner. After a clean there is no groan on wheeling the bike out for the next ride, just the other half groaning in the background .