Front Brake surge

[Speedy1959]

Hi All,

I have an issue which I had once before on a BMW GS1200..
Firstly let me stress that there is ZERO pulsing of the brake lever so I doubt its warped discs!

The problem..
At speeds above say 30mph the brakes work fine and feel very good..
Below around 30mph there is a sort of surging that happens in time with the wheel rotation, so in decreases in frequency as you slow down.
To put it another way its as though there is a patch on the disc/s that is more grippy than the remaining area.

Imagine pulsing your brake lever as you slow..There would be a sort of variation in your slow down rate, instead of the rate being linear.

I must stress again that there is absolutely NO pulsing of the brake lever or any vibration of any kind..
The problem is purely the physical slow down is not a linear smooth rate.

Hard to describe but I have done my best.

[Notty]

Hi All,

I
Below around 230mph there is a sort of surging that happens in time with the wheel rotation, so in decreases in frequency a

Below 230? what have you got under you Simon? 

[T 24]

230 mph. What have you done to your 14, or what bike is it?

[KiwiCol]

It'll be your pads grabbing, spray 'em with WD40 & you'll have a linear deceleration, only thing is the braking distance will be considerably longer than you're used to, so brake early.

Pleased to help Speedy

Right, who's next . . .

[KiwiCol]

Searily though, how about checking the rotor thickness all the way round, not just in 1 spot.  If it were thicker in 1 spot it could throw up that issue.  Dunno how it could get that way - have to be a crook batch of metal used on those rotors or something.

[Kiwifruit]

Meanwhile back at the Salt Flats...... 

Having taken Col's advice Speedy applied his brakes at around 6.15, we expect him to be stopped a little after 9.30 

[KiwiCol]

I did say to brake early, not after tea.

[froudy]

Have a read...
http://blackshadow-uk.co.uk/Fitting.html

[grog]

my 14 at 230mph, asleep and dreaming, i couldnt care less about the brakes. ride on big girl, mustve been the 98 i filled with. totally impressed.

[Kiwifruit]

Good article Froudy.

[Sweaty]

230 mph. What have you done to your 14, or what bike is it?

His name is Speedy after all 

[KiwiCol]

Yeah, what does he want brakes for, with a name like that?   

[Blubber]

Can it be that your discs are oval?

...and thus a variable disc mating / friction area 

[Mick_J]

Had something very similar last year, MOT tester noticed it, I didn't but got an advisory from him to sort it for this years MOT.  I tried everything like bleeding and spinning bobbins but eventually had to replace disks.  First set of disks went rusty in three months but were replaced by EBC, second set seem to be fine.  Good luck.

[Andre]

Besides the obvious checking of the brake system I would take a good look at the tire wear pattern, the suspension setting and fork condition.