RZ front brakes acting up

[Biz]

The front brakes on my RZ are pulsating when I used them hard, and kind of vague for medium use. They pulsate worse when used hard. I replaced the tires cause they were worn unevenly but problem is still there. Calipers were completely disassembled and rebuilt about 5 years ago and they were fine at first but maybe the trackday did them in. Could I have warped rotors? Is this common? Is there a good way to measure for warpage? And are OEM disks the way to go, or what about aftermarket like the EBC or wave rotors sold by Economy Cycle. I have stock calipers and rotors now, about 20K miles.

Biz

[waltmil]

Sounds like warped rotor(s). I'd probably go with EBC but there have been some quality issues I think. Different hole patterns, not bolt holes but lightening/vent holes between disks. Not a functional issue but...

[silverstrom]

Stand in front of the bike and spin the front wheel. If the discs are warped you'll see it.

Might be your calipers sticking and heating things up. No point in replacing discs until you know why they are bent, if they are bent.

Stock discs are just fine and will last forever if you don't cook them. Aftermarket might look cool, but they are either expensive or cheap Chinese crap. Find some good used stock discs. First sort out why yours are bent. There has to be a cause. Until you find it don't install new ones.

[hondaror]

When changing pads, they need to be seated, before you get down to normal braking abuse. If they are not done so, you get uneven wear, pressure points, excessive heating, warping. It's a slow methodical series of heating up the new brakes and seating of the pads. A couple of heat cycles with gradually increasing pressure, and you are set to go.

[Biz]

Thanks for the replies - I will try these things soon! I don't suspect a caliper problem but maybe something went wrong earlier and causes some warpage. Would like to hear from others on good or bad results from aftermarket rotors.

Biz

[silverstrom]

The pistons get crud on them and start to stick. When you remove the pads you can give the brake lever a squeeze or two and move the pistons out past their normal travel. Then you can give them a good cleaning with brake cleaner and a shop towel. That will remove the ring of crud that accumulates. That should solve most sticking problems. If it's more than that the only solution is a strip and overhaul.

If you do decide to use stock discs I should have some here.

[Biz]

I did some measuring today on the RZ front brakes. Didnt have a gauge to measure rotor runout but I inserted a feeler gauge between rotor and disc at different places in wheel rotation. Result, one one disc I could not insert a .0015" feeler gauge in at all, but it does not seem to be dragging. Anybody know what it should be normally? On the other disc there was between .002" and .005" clearance, depending on wheel position. So I've got the smoking gun, a warped disc, about .003" of runout which Is probably causing the pulsing. I'm thinking I will just put up with it for a little longer and fix over the winter. Got maybe 6 weeks of good riding weather left....

[Hooligan]

Warped disks is a bit of a misnomer. Normally the disks don't warp at all. What happens is that hot spots cause the disk surface to be heat hardened or tempered. The problem is that this seems to occur only in spots. You will see this effect as blue spots on the disk surface.

Once there are hardened (tempered) spots on the disk, the softer material gets worn away a bit a leaves those hard spots sitting proud. That is what causes the pulsing that you feel when braking.

If the blue spotting is not too bad, it can be alleviated by sand blasting the disks swept surfaces. I do this at least once every couple of years just to prevent blue spotting and to even out the wear on the disk surface. It also removes any glazing.

[hondaror]

+1, but there still are warped discs, again from heat. It can be very visible, just with the spin of a wheel.

[Hooligan]

Not disagreeing that a rotor can warp but I never saw it in years of roadracing. The blue spotted problem is much more common.

[hondaror]

Not disagreeing that a rotor can warp but I never saw it in years of roadracing. The blue spotted problem is much more common.

Most racers know how to brake. Usually seen on street bikes.

[subxero]

Ever figure out the problem?

Some good advice already on checking the rotors to see if they are warped, and also looking for hot spots and also cleaning the calipers and pistons. These are places to start.

I would also add to the mix just make sure your rotors are super clean, just a little bit of, grease, lube, oil, from a finger smudge on the rotor in a spot or two can cause pulsing as well. Similar to the hot spot, it creates a spot on the rotor where the friction changes which results in pulsing.

[Biz]

Well it's pretty clear that one of the rotors is warped so I'm gonna swap it. Had a lead on some used rotors but it fell through so maybe I'll spring for the EBC's. No signs of discolorization which is strange. Riding season is over around here, I bet in Alberta too :) so this will be a job for next spring.
Biz

[Hooligan]

Not quite. It is 20c and sunny today.

[subxero]

I might have some used rotors laying around that might be in decent enough shape, i can't say for certain though. When i bought my fixer upper it came with boxes of stuff that i have yet to go through. I vaguely remember seen a set of rotors in a box.

PM me if interested, I can dig them out and send you some pictures or whatever and figure something out.