Front brake pulsing ... cured itself eventually.

[utopia]

I've had the oft reported pulsing from my front discs for 5yrs or so, with mot advisories each year.
Its been unnoticeable at speed but rears its head when trundling along in slow moving traffic etc.
I've checked them for truth and even thickness, cleaned the bobbins and gently scoured the surfaces, all with very little effect.
However, the pulsing has been diminishing gradually over the years (as confirmed by the mot tester too).
This kinda ties in with the thinking that this pulsing is often caused not by warped discs but instead by some kind of unevenness in the surface characteristics of the disc.
This is often described as uneven "tempering" of the discs, for which the cure is subjecting them to repeated cycles of heavy braking to get them really hot, followed by allowing them to cool and repeating as necessary.
I've never actually done this, but I did notice a slight improvement after similar incidental treatment during the 2011 Mallory trackday.
Since then I've made a point of occasionally given them the heavy braking routine whenever it tied in with my general riding, but nothing more specific than that.
However, the improvement has continued and has now reached the point where it is virtually unnoticeable and I can once again trickle up to traffic lights on the front brake alone, without pogo-sticking as the brakes pulsed.
It seems that my persistence has saved me the cost of a new pair of discs.

One theory that seems to hold water ('scuse the pun about to be made) is that parking the bike up with wet pads is a bad idea, as they cause localised corrosion of the discs, which will clearly affect their smoothness of operation to some extent.
In fact I've recently heard of a case where this has caused serious, visible pitting in pad-shaped areas on the discs when the bike has been parked up for over a year.

In my case, another possible cause is that my bike had two former owners (both ladies, though I make no gender-based comment here) and neither of them did more than a few hundred miles on the bike.
It could therefore be the case that the discs were never properly used "in anger" in their early life and hence they were never properly tempered.

Either way, it seems possible (likely, even) that the so called "warped disc" syndrome is a misnomer, and that surface defects are the more likely cause.

[AndyC_772]

I've had a minor issue with this on my Diavel, from new. Braking firmly at speed is perfectly fine, but gently pulling up to a halt can be quite jerky. On a bad day I can feel it when pushing the bike around the garage too.

I don't think there's anything "wrong" with the discs, other than the need to use them more than I actually do. Since I rarely brake hard, they probably never get heated or gripped hard enough to clean the surfaces properly.

[Mr Gazza]

..As it happens I gave the bike a good soaking when I washed it yesterday ( It was a reward after a belting long ride out, with beans on toast al-fresco a few yards from the North Sea, pounding it's self onto Norfolk...:thumbsup::biggrin)

So I just went to look at the discs 19 hours after it's wash. Sure enough there is a very slight witness where the pads have sat....Just the lightest possible powdering of biege, which is possible to polish off with a bare thumb and some considerable effort.

Maybe that is the reason for the slight tremble from the brake lever sometimes? Never a full throb on, so I choose to ignore it, as it is not consistant and mostly never there at all.

The discs are about 6000 miles old Arashi wavy ones which have improved in thier feel and power since I fitted them, and seem to wearing very flat and even with the EBC organic pads. They are Stainless, and I had never noticed any "browning" until I looked very closely just now.

Both the Brembo discs that they replaced were definately warped in a big way. I noticed it all of a sudden on the way home from East Kirkby (The day we met). Checking with a dial gauge revealed two bumps on one disc and a huge one on the other!

"Pad patches" were a common occurance on my Triumphs with iron discs, as the bright surface would soon go brown at the slightest moisture. I can't remember any pulsing with those though...Perhaps a bit of crunchyness as the pads took the "brown" off first time round, but otherwise very good brakes indeed.
I would always skim the original Chrome off though. The Chrome would tend to come off rather unevenly, if left to it's own devices, and not only look awful but give the pulsing thing of which we speak....Still a big improvement on Triumph's insta-fade Comical hub with water scoop... :chuckle:

[damien666]

Interesting. I'm not a heavy braker either as i usually carry ballast ( pillion). I have also noticed a very slight rub or grab at slow speeds like pulling up at junctions. Original discs which look visibly new.

[utopia]

Yes, I was out on the bike yesterday too.
Who'd have thought it ... 70 bone dry, warm miles back from Shropshire on boxing day !!
And no salt .. not just from this year but they didn't spread much last year either, so no build up in the "dead zones".
Unlike the previous year when grit residue persisted off-line throughout the summer after heavy winter applications. !!
In fact, now that I think of it, the salt levels probably contribute significantly to the patchy disc corrosion.
Maybe this is why they've shown such an improvement this year, with the reduced amount of salt spread last winter and the heavy rains to wash it away quickly too ... they do seem to have improved more rapidly recently.

[Mr Gazza]

I am blessing the absence of salt and the position of the Jet Stream too.
Yesterday was a mega-bonus....Each new ride is treated like the last one of the season and is enjoyed to the full...Looks like the new year will see it getting colder?

It's not at all unreasonable to assume that salt will make the "pad patch" thing worse, even though the discs are Stainless. They will still have a significant iron content.

I was quite suprised to see my little patches of oxide though, as I had washed with a shampoo and rinsed with cold clear water...Which should both have been free of salts coupled with the salt free roads.

I got to thinking that possibly, maybe, there is a weak galvanic/electrolytic proccess going on? My pads are organic, but I am sure that they do contain metal of some sort. Metal is very evident in sintered pads and looks like copper or bronze or some alloy thereof. But whatever, I bet it's higher up the galvanic scale than the iron in the discs...I wonder?

Makes me wonder if the little springs I once fitted, to push the pads open, might help the "pad patch" thing too? Also thinking I might get the bike up on the front stand and spin the wheel to let the pads wipe the disc before a potential lay up....I might even push the pads back a little to keep them off the disc if the lay up looks like setting in for a bit.

[utopia]

Yes it sure is a bikers' winter so far.
I've had to put mine back together once already.

Perusing Wikipedia (I only skimmed it) ......
Yellow metal alloys are below iron/steel so would corrode as the anode, not the steel.
However, at the top of the list is graphite.
Maybe there is a carbon content in the pads which causes anodic/galvanic corrosion of the discs ?

https://en.wikipedia.org/wiki/Galvanic_series

I also thought about sticking the front on a stand and spinning the wheel but I reckon you could achieve a large part of the benefit just by moving the bike forward and/or backward at intervals, maybe a couple of times ... rather than the fuss of the stand.
And not just when laying the bike up either.

I'll be fitting full-floating bobbins which might allow a little more air in there perhaps ?
And I still like the little springs idea.

Oh, and I doubt that its relevant, but I did fit titanium pad pins recently (courtesy of Big-Oz, whose generosity deserves a mention here ... thanks again, mate).
They do seem to allow the pads to release a little more fully and the brakes feel a little more "slick", but its a fairly minimal effect and unlikely to have affected the pulsing, I would have thought.

ps. I've considered using a hair dryer to dry the pads too, but it seems like a bit of a chore.

Couldn't we suss something out involving the front stand and a hamster ?

[Nickj]

They do neeed a good hammering from time to time to keep the surfaces working properly. I did put up a post about this somewhen.

My pegaso winter hack came with a bit of a pulsy front disk, it hadn't really been used that much.. now it is getting used (OK abused) and the braking is smooth as you like.

[Mr Gazza]

So probably nothing in the galvanic idea then? Although if there was anything in it, it would be made worse by a saline elecrolyte?

I think Nick has it with the regular use idea, but that wet doesn't help things.

I can't see your floating bobbins letting any air in? But you might be able to manually push the discs sideways to back the pads off a little. Either after a wash or at the end of a wet ride.

I have access to two hamsters and two guinea pigs...:thumbsup:

[utopia]

No, I'm saying that there might be something in the galvanic idea actually, but only if there is a carbon content in the pads, which would provide the cathode.
Or indeed some other, non-metallic element perhaps.
I was being lazy though because I have no idea whether some/all/any pads do have any carbon content, and I didn't bother to check.
I probably will when I have a moment.
But I have heard "carbon Lorraine", "carbon ceramic" and other such terms bandied about in connection with brakes, so its not inconceivable that the non-metallic element of the pads could contribute to galvanic corrosion.

And I think yes, the saltier the worse, probably.

And the floating bobbins ... I was just thinking that their ability to cause less drag must also mean that air can get between pads and disc just that tiny bit more easily ... and sometimes its the little things that make the difference (particularly if you can add one or two together).

But and Also, it has been suggested that I point out that all this is mere supposition.
It is based on some minimal indications and is by no means intended to be proven in any way.
Just food for thought and general chat.

And guinea pigs are fat little fekkers.
I'd leave 'em out ... too much unsprung weight !
But .. is it rotating too ? .....:spin:

[boris]

Interesting thread. I had an Advisory for the same on my 620 in '07. I did the standard checks and couldn't find anything out of tolerance that would have given cause for concern. The following year, and subsequent MOTs were all clear with the same discs and pads fitted??

[gary tompkins]

Sounds like disc buttons are seizing. Had the same issue on trike once. I sorted by removing discs from wheel, giving them a good clean and soak in penetrating oil overnight. I made sure the bobbins were free the next day, cleaned off excess oil with brake cleaner. Refitted them and bingo... problem solved :)

[utopia]

I think I forgot to mention ... in my case one of the first things that I did was to clean the bobbins.
I used the method which employs a bolt fitted through the bobbins to turn them, while spraying with brake cleaner.
In fact none were seized although they were holding lots of dust.
No improvement, though they did sound different afterwards.

[slob]

Remember the pads are just hanging from the pins, they shouldn't need pushing back,
The elastic deformation of the seals is what releases the brakes, when hydraulic pressure is removed the seals regain their original shape, pulling the pistons back into the calipers.
http://www.thelasturl.net/img/brakeseal.jpg

[Dukedesmo]

Remember the pads are just hanging from the pins, they shouldn't need pushing back,
The elastic deformation of the seals is what releases the brakes, when hydraulic pressure is removed the seals regain their original shape, pulling the pistons back into the calipers.
http://www.thelasturl.net/img/brakeseal.jpg

Interesting, and it explains why changing old seals (other than if leaking) might help improve the brakes.

[Darren69]

I think also the pressure changes from the fluid when you release the level will also pull them back.

[Mr Gazza]

I remembered this tread this morning, when I came to a crossroads and caressed the front brake up to the line.....And there it was...The gripslipgripslipgripslip thing.

It was the first ride since Boxing day, when I gave it a good wash and observed the slight oxide patches under the pads. (post #3)

I've lost count of how many times I've laid the bike up this Winter, but a January ride is a very unexpected bonus..Maybe this is the final lay up?

So I remembered the brakes again as I approached the same crossroads from the other way on the way home.
The road is straight, dry and empty, So I wound up to some considerable knots and gave the front brake a good long hard pull....Coasting the last few yards with the brake sensitively feathered was as smooth as an Oyster slipping down Holly Willoughby's throat.

...And that concludes the case for "pad patches" for me.

[Darren69]

I think I would most likely crash if I thought that about Holly Willoughby when braking!

[utopia]

Good info there, Gazza.
I'm now fairly convinced that this is one of the mechanisms which cause brake pulsing.
I doubt that its the only one, and it may not be the most significant but I would wager that it is part of the picture.
Furthermore, I would wager that it is highly likely that it can operate in conjunction with other factors involved in the "surface conditioning" of discs, and may make those factors even more significant.

I have now removed my discs and the plan is to fit fully floating bobbins.
I am not going to clean or abrade the braking surfaces in any way though (much to Capo's consternation), and thus I hope to be able to detect if they have any benefits in this area.
Of course that's not WHY I'm fitting them, but it could be a useful secondary experiment.
I'm not holding my breath though ... its a long(ish) shot.

ps. I found your edit amusing !!