Diagnose brake feeling

[D6]

I am thinking I know what it probably is but thought I'd get a second opinion.

When I bought my bike the brakes seemed pretty good. Not the initial bite the Kwack had, but still strong and more than adequate.

I then fitted new (to me) forged wheels, which came with new (to me) brake discs.

The wheels and discs had only done a tfew hard miles, but looked brand new still. No marks on the wheels at all, and the discs looked fine.

After fitting them, I was sure the braking performance wasn't as good, but as it was winter when I switched (and constantly wet) I couldn't be sure.

I had the impression of a slight vibration when braking.

This is now definantly what is happening now it's finally dry again and I've been able to do some hard braking.

It even showed on my bike cam when I braked as heavy vibration.

I notice that when filtering and riding very slow, if I squeeze the brakes slightly I get a bit when it brakes, then there's not much firction, then brakes again. etc.

I am thinking a warped disc or somethign like that. When hard braking it kind of feels like it fades as well as the vibration. Another option was glazed pads, but I don't think that would cause the vibration.

It's annoying if I need to replace discs.... I still have the old wheels, but it means changing shims for the ABS sensor, different spacers and changing tyres.

[Perkles]

you dont need to replace them ,get them skimmed
you should never use different pad compounds on the same disc they probably have picked up some material from the pads which would cause the judder,if they were warped they would do it all the time

[Kwacky]

Have you checked each of the bolts on the discs to make sure they're threaded correctly?

[DaytonAndy]

Have you done many miles with the new (to you) discs fitted? It would take a while for the pads to 're bed' to the new discs. Should really do new pads but they should still bed in. Also did you clean the discs with brake cleaner or similar?

[DaytonAndy]

I would also say get someone else to try them. I always over analyse things on my own bike!

[D6]

Thanks for the advice all. I have done about 6000 miles on them, so think they should have bedded in by now. When they first felt rubbish, that was my other thought.

Obviously I don't know what pads the otehr person used, but as it was a brand new speed triple R, I would imagine it was the same barnd of pads. In fact I'm 99% certain.

Havn't cleaned the discs, but there's a noticeable virbation. I suppose this could eb caused by gripping and sliding though. Not though of that. Maybe try some brake cleaner first then.

Kwacky, I've not checked any bolts. Which do mean? the floaating disc things or the actual fixings?

[DaytonAndy]

Have you bled the brakes at all recently? Might be worth it?

[DaytonAndy]

Also is the vibration definitely coming from the brakes or up by the headstock area when you brake?

[D6]

Not bled the brakes, but my serive is (over) due so maybe I'll get them to sort it and see.

It's hard to tell but I am sure the vibration/pulse is coming from the disc. I cant say that I feel it through the lever though which is what I have heard you would if it was a warped disc.

It is almost like a very mild ABS kicking in.

[Kwacky]

The bolts to screw the discs on to the wheel. If one is loose or not on correctly I think that can cause vibration.

Another suggestion is the brake calipers. They might need cleaning.

[Perkles]

Not bled the brakes, but my serive is (over) due so maybe I'll get them to sort it and see.

It's hard to tell but I am sure the vibration/pulse is coming from the disc. I cant say that I feel it through the lever though which is what I have heard you would if it was a warped disc.

It is almost like a very mild ABS kicking in.

get some brake/clutch cleaner and a scotch brite pad and clean your discs thoroughly that will eliminate any material pick up.I had the same issue on my 911 at spa and it drove me mad but it was only pad material on the discs

[Blade]

Have you got a DTI or access to one at work ? If yes very easy to check for run out.

If not remove the disc and place on a flat service and see if you can get a feeler gauge under any part of the disc.

If the disc is flat I would suggest the problems is pad material on disc which needs removing or incorrectly mounted discs.

[duke63]

I'd check the pads and pistons are moving freely and squarely before doing anything else, D6.