What's happening to my brake discs?

[Fallout]

So I bought the Shed over a year ago (GSXR 750 K1). When I test rode it, the brakes were fine and they were fine for a period of initial ownership. Then they started to 'warp' or whatever, got lots of judder. It got worse and worse until it was down right lethal.

I bit the bullet and got some second hand discs. I also completely rebuilt my callipers, new pads, and even got a new front wheel and spindle. The brakes were true for a while, and now slowly they're 'warping' again. WTF?

So to recap!!
- Bought bike, no problem.
- Judder started and got worse and worse. Could spin the wheel and it would noticeably spin free then lock.
- Got so bad I was about to die.
- Bought 2nd hand replacement discs
- Overhauled callipers
- New pads
- New (2nd hand) front wheel
- New spindle
All perfect and hunky dory again ... but now the problem is starting again. Pad wear is all even and normal.

So the only thing really that is consistent is the forks. The only thing I can think of is the callipers are misaligned against the discs due to the forks (or the bracket the callipers connect to) not being lined up properly. Otherwise I'm at a complete loss. Any other ideas?

For the record I'm very easy on the brakes for the most part, so they don't get hammered.

[DarrenSV650S]

Master cylinder knackered?

[atassiedevil]

Master cylinder, or warped wheel perhaps?
does the wheel run true? Could the spindle be bent? You'd see this issue with both.

[andrewsmith]

Master cylinder
Twisted, or bent forks.

I'd get the bike up and remove the forks and reinstall them and align them before nipping the yokes

[Fallout]

How can the master cylinder have anything to do with it?
How can it be a warped wheel or spindle when both have been replaced and both times it was fine then slowly became a problem?
Are you all drunk?! :D

Twisted/bent forks seems like the only possible culprit really so far. Removing them isn't something I've done before though. I wonder if there's a way to check alignment before I go that far? Googling for vids now!

[BBadger]

I'm thinking forks more than anything.

Only real way is to take them out and check, but you can always loosen the bolts (make sure the bikes weight is supported 1st ) the give the whole front end a good giggle and whack....any movement will be heard as te metal moves due to the bolts still being tight enough to create the friction.

Also more than happy to help out with it all.

[Bibio]

nope if your getting pulsing like ABS then its the discs have been out of true when fitted, the mating surfaces of the wheel hub and the disc have to be meticulously clean.

what happens is that the surface of the disc starts to get 'peeks' and 'troughs' as the pads ride over an area and these just get worse as time goes on. warped discs are very rare.

classic symptoms are the brakes feel fine then you start getting a very slight judder/pulsing when braking then it just gets worse until the brakes feel like old 80's ABS until the bike is eventually unridable. it's usually not felt when not on the brakes but as soon as you start braking it starts pulsing.

cure is either resurfacing of discs if they are still good nick or new discs.

i know this is going to sound a bit OTT but when you fit new discs use a runout gauge to check for true if the gauge shows more than +-0.25mm you need to take it off again and rectify it or the same will happen again.

[Fallout]

I almost bought a run out gauge a while back, but didn't spend the dollar because I am cheap. Cheers for the advise though.

I think what I'll do is do some fork realignment as per his video ...

vSunBRB6-r8

As that's quick and painless. I'll see if that makes anything feel different. If it does, I'll ride it for a bit and see if the problem at least stabilizes. After that I'll get the discs off and thoroughly check the hubs/discs for dirt etc. then tighten them down properly again. Will probably ask around to see if anyone has a run out gauge too.

Cheers guy. Cheers Brock for the offer of help too. :)

[Bibio]

take it from me they are fubar. i had the exact same thing a few months ago.

took the discs off cleaned them checked alignment etc.etc no gain even fitted new pads. BTW i fully strip and service my callipers every year so know my brakes are in tip top condition.

[Red Herring]

You haven't mentioned disc colour. Are there any blue spots or signs of overheating?
Is there a lot of brake dust on the rims? I'm just wondering if the brakes are binding slightly. If you are happy with the calipers is the master cylinder returning on it's stroke completely.

[Fallout]

The pads may be binding now. I don't think they were before, but now the pads lightly scuff the surface each time you spin the wheel. Enough to stop it after a few revolutions when you spin it off the ground. I know that's not a lot but maybe it's making it worse now. It actually moves the pads slightly in the calliper with a little "click" which is why I wanted to get it sorted out.

Bibio, I'll take your word for it they're fubar ... AGAIN. But if I can sort it to some degree before I replace the discs, that'll stop me going through yet another set. I'll try the fork alignment and replacing the discs on the hub.

[millemille]

Check that the bobbins which connect the carrier to the rotor and allow the rotor to float aren't all gummed up with brake dust and detritus and have seized, meaning that the rotor can no longer float and expand/move as it needs to as it heats up.

Many oem disks are known for this.

A jewellers screwdriver, toothbrush and brake cleaner used to pry the bobbin to one side and then scrubbing and blasting the crap out of the gap will free it up, repeat this for all the bobbins.

[Sid Squid]

Those bikes were notorious for this, we're the replacement discs OE parts? If yes then my advice would be good quality replacements - PFM, Brembo, Grimeca for example.

[Bibio]

the pads are scuffing the disc due to the raised part (peak) of the disc/s, the click you hear are the pads rising and falling in the callipers as they grab the raised part of the disc. pads are loose in the callipers which is perfectly normal.

you could try as others have said and clean the bobbins but i doubt that it will work.

[Fallout]

I cleaned the bobbins in my last set. They could spin and the disc 'floated' pretty well. This new set the bobbins were pretty tight but clean. I took it out today and the issue is pretty minor. I feel like if I can sort out the cause now I might be able to prolong the life of these discs, so gonna try the fork alignment and check the mating surfaces of disc and hub before the next ride. Thanks for the advioce (yes, said in an American 30s gangster accent).

[Dave20046]

I'd bet it's the calipers (are they tokico by any chance?), try a different set (I know you;ve said they were overhauled but the pistons could still be coming out cocked to one side.

[dirtydog]

Reminds me I still have to swap the front discs on the SV. Couple of really loose bobbins on mine, I also got some 2nd hand ones as funds were tight at the time.
Hopefully they last longer than fallouts!

[Sid Squid]

If the pads are flapping about in the calipers something is wrong - it's far from normal.

[embee]

From the description of it being a progressively deteriorating thing, my thoughts would be towards irregular transfer of pad material to the disc surface.

If they were mine, I'd take the discs off and generously rub down the surfaces with something like 80 grit, working diagonally across the braking surface so they end up looking like a spiral pattern. Use a sanding block to keep the surfaces as flat as possible. It'd be worth doing the pads as well, though you do have to be a bit cautious on pads not to get abrasive grit stuck in the surfaces.

The brakes then need to be bedded in thoroughly, progressively increasing the speed and rate of braking, don't be too gentle.

On other bikes, people have "cured" similar issues by using different branded pads, Carbone Lorraine seem to get the nod but others' experiences may differ.

Just my thoughts. :-k

[Littlepeahead]

If it's happened more than once it might be the Missus trying to get rid of you. Or the dog. Have either of them taken out life insurance for you?