No Stopping Power - Bad Rotors?

ARWUN · Jun 4, 2003

I bought a front wheel with rotors off of e-bay to use for a track-only wheel/tire set-up. I put a new tire on it tonight, and took it for a test ride… big problem – I have hardly any front brakes. The lever squeezes down very far. When I am stopped, I am able to pump them up, when moving there’s not much there. After the quick 2-mile test ride I looked everything over and noticed from the fresh wear marks on both rotors that my pads are only touching at the outside & inside edges (all four sides). It’s like the rotors are concave, or my pads are concave. It would seem like my pads could wear to match the contour of the rotors after a few hundred miles and a bunch of brake applications, but that would unnecessarily wear out the pads, and I need them to work for the other set-up as well. Plus, I wouldn’t have much braking available in the mean time.

What the hell is going on? I didn’t feel any pulsations while riding, so I don’t think that they are warped. Although, I did spin it before installing it and noticed a very slight wobble compared to my stock rotors & wheel. Do the new rotors need to be turned? Does anyone do that with motorcycle rotors, or are they too thin? The new ones are off of an R6, and actually have less wear (more thickness) than my stock ones.

I am leaving to go to Road America on Saturday, and then planned on using it on the track on Tuesday & Wednesday. Please help! What should I do? Use my original rotors on the new wheel? That was the reason that I bought a wheel with rotors, so I wouldn’t have to do that.

Eyespy · Jun 4, 2003

If they wobble that's the problem. The pads are getting pushed back in the calipers as the rotor spins. It will never work right like that. The carriers or rotors are bent.

turd1 · Jun 4, 2003

put a straight edge on the disc to check warp or concave, or better still set up a magnetic dial indicator to check runout!:fact

ARWUN · Jun 4, 2003

Eyespy said:
If they wobble that's the problem. The pads are getting pushed back in the calipers as the rotor spins. It will never work right like that. The carriers or rotors are bent.

Are you speaking from experience, or just trying to come up with a theory?

If the runout was excessive, wouldn't I feel it while braking? By eyeball, I would guess that the total runout error is about 1/16" on the one rotor, and the other one is good. Both of my stock ones look to be true. I understand what you're saying, and it seems plausable. But, would the one bad rotor cause the other one not to work properly? Also, if that was the case, wouldn't I notice the wear marks to be only in certain sectons along the rotors (hitting - not hitting), instead of all the way around at the outter edge and inner edge?

Here's a theory: I got my stock rotors very hot at the track. When heated, the inside was hotter than the edges, and expanded more causing the rotors to bulge out in the middle and become convex, making the pads concave to match. Then when putting the pads on the new rotors that are still flat, only the edges of my pads are touching.

One problem with that theory is that my stock rotors would go back to flat when cool, and they don't feel like these new ones do initially. I am almost pulling the lever all the way back to the grip!

ARWUN · Jun 4, 2003

What's the chance that the new rotors weren't bedded-in properly, or were overheated, and that's why they aren't grabbing?

And, why did I lose my lever pressure?

pitbike · Jun 4, 2003

If you have no shudder or wobble, nothing is leaking and there is plenty-o brake fluid in the system....then you have glazed pads. Get new HH pads, clean your rotors with Brake Cleaner and you should be good to go.

ARWUN · Jun 4, 2003

My pads were fine two minutes earlier when I used them with the stock rotors. However, there may very well be something wrong with the surface of the new rotors. They had a little surface rust on them when they arrived; I can't tell if they're glazed, but they may have been overheated, or something.

ARWUN · Jun 4, 2003

So, I guess the next thing to try is to swap rotors with my original ones, and see if it fixes the problem?

If so, that'll get me through the track days at Road America next week. But, I'll have to figure out something for the rest of the season.

No Stopping Power - Bad Rotors?

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