Norge front discs (again?)

[Bison]

Hi Folks,
Greetings from a rather damp Scotland.
2007 Norge
OK, front brake is not pulsing or juddering at the lever, but, when I've almost stopped, maybe 5mph to zero, it's like I'm pulling the brake lever on and off, the front end dives then rebounds, dives then rebounds. New  pads, and the rotors were replaced with EBC ones maybe 9000 miles ago. I've loosened off the bobbins using the bolt through the middle trick, but here's the thing, the bobbins are not sticky now, but they don't rotate any more than maybe 10 degrees back and forth, IE they will move back and forth radially but not in a full 360 degrees. Am I missing something here?, I would have expected them to rotate 360?. No dull spots on the rotors either, indicating a warped disc.
Any suggestions or advice warmly welcome.
Thanks.
Alan.

[Huzo]

Ok.
If the lever is pulsing, then that would indicate the pads moving in and out with a fluctuating disc surface.
You say the lever is not moving as the braking on/off feeling manifests, so I’d look towards some contaminant on the disc, this would give the on/off braking sensation you describe.
Sure it’s good if your bobbins rotate, but suffice to say that if you can get some rattle from the disc then it should be able to self align.
I cannot tell you why you are not getting a discernible “juddering” at high(er) speeds and braking pressure, but start by cleaning the discs properly and make sure the holes do not harbour contaminant.
BTW.
When you say the bobbins will move radially, do you mean rotationally ?
Radially means by definition, in the same direction as the radius. It sounds pedantic, but you must be specific.
Radially would mean in and out towards the centre of the wheel and the perimeter and that would not be measured in degrees, but millimetres.

[Bison]

Hi Huzo,
I hope you are well.
I mean, as you say, rotationally, the bobbins will rotate around their own centre with a bolt inserted, but only a limited amount of degrees, my other bikes rotate a full 360, round and round.
No pulsing at the lever.
I'm just back from the Auto supply store clutching a new tin of brake cleaner, I'll give the discs a going over with green scotchbrite  and aforementioned cleaner and see how that works.
Thanks.
Alan.

[Tom H]

Hopefully a good cleaning solves it.

Just a thought. Does the bike have ABS? Could it be acting up at low speeds?

Tom

[Huzo]

Hopefully a good cleaning solves it.

Just a thought. Does the bike have ABS? Could it be acting up at low speeds?

Tom

If the pads were moving, he’d feel it at the lever.

[Bison]

Hi Folks,
Well, scoured all the discs with brake cleaner and green scotchbrite pad, cleaned and checked all the bobbins, removed the (new) pads, cleaned out the grooves, the pads are not sticking manually in the callipers ,checked and cleaned all the calliper pistons, without stripping the callipers, they are all working fine, no binding on the wheel, it rotates fine, but still the same.
Yes, it does have ABS, and I hadn't thought of that, is it possible the abs is acting up?, maybe clean and check the sensor?. When you are at low speeds and lightly pull on the brake lever you can feel the suspension starting to pulse, the more you pull the more the bike dives then returns, just like it would if the disc was warped. I checked the steering head bearings, they are fine, no play, and replaced about 6k miles ago with tapers. I looked at the disc for dull spots where the pads aren't contacting that part, there doesn't seem to be any.
Looks like I'll need new discs, but it doesn't add up?
Alan.

[Frenchfrog]

But if you bobbins are not floating correctly as you mention in an earlier post then that is surely adding if not causing the problem ?Sounded if they might have ovalised for some odd reason...

[Bison]

Hi,
All 10 of the bobbins are the same, they move easily, but only back and forth slightly, rotationally as Huzo pointed out, I'm loath to force them incase they are meant to be like that, but if they are, they're the only ones I've come across, on all my other bikes they just rotate.
Alan.

[Bison]

Folks,
Another question if you please, do the brembo callipers have an anti squeel stainless shim between the pistons and the back of the pads?, nothing on mine. My pads are fitted dry, that is, no hi temp brake grease on the back of the pad where it contacts the pistons.
Oh and for the sake of clarity the problem was there before I replaced the pads.
Alan.

[Huzo]

There is a button on the lower left fairing panel about a foot below the left handlebar, it has “ABS” on it.



If you push that, it disables the ABS, push that and go for a ride and try it.
There is a yellow light that flashes when it’s de activated. It re activates when you turn the key off and back on again.

[Huzo]

Folks,
Another question if you please, do the brembo callipers have an anti squeel stainless shim between the pistons and the back of the pads?, nothing on mine. My pads are fitted dry, that is, no hi temp brake grease on the back of the pad where it contacts the pistons.
Oh and for the sake of clarity the problem was there before I replaced the pads.
Alan.

There are no shims as standard.
The bobbins should rotate.
Have you put a dial gauge on the discs in situ and spun the wheel ? That will detect any run out.

You can of course take one caliper off, place a 1/4” packer between the pads and with the caliper removed and taped up out of the way,  go for a ride and squeeze the brake as before.
If the problem persists, it’s not in that caliper, if it goes away then it is.

Even if your bobbins have worn into an oval shape, that should not prevent them from turning.
Can you rattle the discs ?

[Bison]

Lots to try here folks, thanks.
Huzo, I can move both discs , but rattle?, no. First thing to get going is to rotate those bobbins. After that, if still the same, I'll use a bit of stock 8mm steel I have to do the calliper test. It points to a problem with the bobbins if they are meant to rotate I think.
Yes, I put a dial gauge on about a month ago, and found some deformation, but less than 5 thou, my problem feels as if it would have to be out by more than 5 thou.?.
An abs deactivation button?, in plain view?, that I know about?, but completely disregarded!, hehehhe, don't let anyone tell you old age comes by itself!, thanks.

Alan.

[tazio]

Bison, keep the Faith. You'll figure it out.
If ever an issue "resolved itself" it would be my exact issue your describing.
I replaced pads,measured,cleaned, wire brushed, spun bobbins etc.
No luck. Finally broke down and bought new rotors with intent to change at new front tire replacement.
4 months later and ready for new tire, I realized ISSUE GONE.
 HAD to be imbedded contaminate in rotor.
Went ahead with new rotors anyway
(Kept good originals)

[Huzo]

Here’s another definitive test..
If your discs(s) is/are warped, they will be a bit like a wave washer and have multiple ups and downs around their perimeter.
If it’s your bobbins, the disc will be flat but just misaligned to the plane of the wheel.
Now..
Because your wheel is about 6’ in circumference, a straight disc misaligned, will pulse at intervals of about 3’ as you slow down, whereas a warped disc will give a higher frequency to the pulse..
Try that test.
Also.
When you apply the front brake in a medium stop, I’d be very surprised if each pad moved more than 15 thou’, that’s what my example revealed.
So the point I’m making is this..
A disc with 2.5 thou’ of runout will have a total fluctuation of 5 thou’ and I suggest that represents a moderate brake application.
You suggest the dial gauge indicated as such….
I could work out the travel on the pads by knowing the volume of fluid displaced in the master cylinder and knowing that is spread out over 8 pistons in your calipers.
For example.
If you displaced 2 cc of fluid in your m/c, you’ve displaced 0.25 cc of fluid in each piston.
Knowing the diameter of the piston will give you the stroke.
Volume = area x stroke
So
Stroke = Volume/area

Don’t bother working it out if you don’t want to, but I bet it’s no more than 5 thou’.
Point is…?
Five thou’ is enough to make the braking uneven. I still do not know why it does not manifest at high(er) speeds.

[Bison]

I'm pretty sure it pulses once every wheel revolution, so it points to bobbins.
Tomorrow is turn the bobbin day.
Alan.

[Huzo]

I'm pretty sure it pulses once every wheel revolution, so it points to bobbins.
Tomorrow is turn the bobbin day.
Alan.

Sounds good.

[tris]

Assuming that the bobbins are free and discs not warped, I'd consider a bit of an Italian tune up.
Find an empty stretch of road,  bring the bike up to  a reasonable speed , brake hard to a near stop, and repeat several times.
Don't go a silly speed, or bin the bike!
My B1100 used to do something similar to your bike, and I think that it was caused by pad material sticking to the disc as I don't tend to work my brakes very hard.
Working the brakes hard cleans the discs and forces them to move about on the bobbins

[g5guzzi]

I'm pretty sure it pulses once every wheel revolution, so it points to bobbins.
Tomorrow is turn the bobbin day.
Alan.

it may pay to check the EBC website . i seem to remember
reading some discs were fitted with square bobbins.

Malc

[Huzo]

it may pay to check the EBC website . i seem to remember
reading some discs were fitted with square bobbins.

Malc

Jeez.
That would have got me…

[Bison]

Morning Folks,
I did a little more research, yes, EBC discs are indeed fitted with square drive bobbins, which ensure the rotors will never distort again, hehe, just as well I checked before getting the power bar onto it!. Then on opening up the post here I found G5Guzzi's post.
ABS check then, and after that remove a calliper to find which side is causing the problem.
Alan.

[Paul_Tim]

Similar to the problem I had on my 08 Stelvio, tried the cleaning pads etc, checked bobbins free, resorted to engineering and attached dial gauge, one disk showed warping. On removing disk and using a surface table it turned out to be a bent disk carrier rather than the disk itself (I suspect a less than careful technician when changing a tyre).
You could get the same effect if there is contamination between the disk and the hub which causes it to be offset.

Probably neither of these but just throwing it out there as a possible alternative.

[Bison]

Hi Folks,
Well, for info, the bobbins on the EBC discs are indeed flat sided, and they were a but sticky, you free them by moving them in the direction of the spindle, then the tyre,  with a drift on the centre of the bobbin, back and forth, the discs rattle slightly now, but the brakes are still the same. I put a dial gauge on the outermost part of the carrier .07mm, I make that .0028". I switched off the ABS, no change. Later I'll gauge the outer part of the rotor, and also the thickness at a few points around the circumference, but I think I'm looking at new discs. I know it's a lot of faffing around, but new discs aren't cheap, so I would like to make sure.
Alan.

[Bigtime]

  I always remove my discs before taking my wheels in to have new tires mounted. I'm concerned that the shaved ape(Pete Roper term  ) in the back will bend a disc or carrier. Good time to give them a good cleaning also. Just finished the front on my Norge yesterday.