Bit of a detective one here – wonder if anyone can help.
About 9 mths ago I got the front brake pads replaced on my 2005 blade, uprated to something a little sportier at FWR. Upon bedding them in I got fairly massive vibrations upon braking from anything above 60. This hadn’t happened with the old pads, which admittedly were crap.
Took the bike shortly after to Lydden Hill for a track day with about 100 miles on the new pads and braking from about 90 the front end felt it was bobbing up and down violently. Thought it might get better once they’d bedded in, and it did to a certain extent. A mate who’s very handy with spanners reckoned it wasn’t a warped disc (front wheel spun fine on a paddock stand) but rather a build up of gunk on the callipers. Shortly thereafter took it to Steve Jordan to get the suspension re-done and asked them to have a look at. They cleaned out the gunky brakes and it seems fine, although still not perfect.
Haven’t really used the bike for much in the way of tracks and high-speed riding until a recent trip to Germany and found then that at relatively high speeds such as over a ton and I get a pulsing / vibration through the bars. Just a touch on the lever at about 140 (bloody Porsche drivers…) and the vibrations were really not very nice.
So – any suggestions as to what may be the cause? 30k miles on the bike, braded lines, fluid flushed relatively recently. Gunky callipers again? V slight warp disc(s)? both?
Agreed. Warped disc(s) is the most likely, but funny things can happen from things as simple as the pads sticking on the guide pins, contaminated rotors (discs) and, just once, a disc where the braking surfaces were on parallel.
why not, before resorting to something dear like new disc’s, dont you try putting a cheap set of pads back in, and seeing if its the same, maybe, its the new pads at fault?
Many thanks all for most useful replies. Is there any easy / not too expensive way to check the discs for warping other than buy a new set and hope that this fixes the issue?
I wouls suspect Warped disks although I would also do a careful check of the callipers as even slightly sized callipers will warp the disks
You can do a check with the bike on Paddock stands yourself by spinning the wheel and using a pencil or screwdriver as a pointer but it really need a Dial indicator on a stand to do a proper check
So brief update on this FWIW: took into local shop whose work I rate highly and they checked alignment and callipers sticking, with neither being an issue.
What it looks like is some slight corrosion / pitting on the disc surface on both discs from where the bike may have been left standing for a while before I bought it. The pitting is about pad size and in the same place on both discs, so seems to support this theory. It’s only become noticeable with uprated pads that grab the discs more firmly, especially over the rough pitted surface, leading to the pulsing feeling. Discoloration on the discs starts where the pitting starts and then fades around the circumference of the discs, indicating heat build up from the greater friction from the pitting.
Again, only an issue on heavy braking about 90 or so, so fine for the roads just not great for the track. Looks like a new set of discs for me then maybe after the rigours of the winter.
Massive thanks once again for all the suggestions and comments – really helpful!
Can you not get them re ground (or whatever the process is called) by somewhere like ABE? Might save a few quid on getting new discs if you go that route.
Warped / pitted / causing vibration can still have an effect on your tyres and pads… Just because you are not feeling the pulsing at lower speeds does not mean it is not happening…
The suspension and the flexing of the tyres themselves will hide the pulsing at lower speeds.
That pulsing can cause extra stress on your bearings, etc, and if you wait too long, the knock on effects to other components could be costly.
Motopup’s advice is good advice. Whatever you do, get it sorted.
The following has been taken from wikipedia.org
search: google, brake disc, first result
It is quite interesting but to save you reading it all, under the heading Brake Judder is this:
Assuming it is brake judder there can be 2 types hot or cold:
Hot judder - usually produced as a result of longer, more moderate braking from high speed where the vehicle does not come to a complete stop.
Commonly occurs when decelerating from speeds of around 120 km/h (74.6 MPH) to about 60 km/h (37.3 MPH)(this sounds like your scenario?), which results in severe vibrations being transmitted to the driver.
These vibrations are the result of uneven thermal distributions, or hot spots.
Hot spots are classified as concentrated thermal regions that alternate between both sides of a disc that distort it in such a way that produces a sinusoidal waviness around its edges.
Once the brake pads (friction material/brake lining) comes in contact with the sinusoidal surface during braking, severe vibrations are induced, and can produce hazardous conditions for the person driving the vehicle.
Cold judder - The result of uneven disc wear patterns or disc thickness variation (DTV)(this is not the same as a warped disc).
These variations in the disc surface are usually the result of extensive vehicle road usage (yours disks have done 30,000 miles, post above mentions they change them at 35.000, so could be close to their limit?).
DTV is usually attributed to the following causes: waviness of disc surface, misalignment of axis (runout), elastic deflection, wear and friction material transfers.
I think the solution for the above would be to skim the disks or change them if the disk thickness is less than recommended.
That pretty much sums up my issues with hot spots and vibrations at those speeds - excellent find so many thanks indeed for the info. New discs for me now ordered!
