Brake rotors.... need help

[uclabiker06]

Front brake would pulsate and I assumed it got warped when i accelerated w/ the disc lock on.  Got a oem rotor from ebay to replace what i thought to be a warped rotor.  Now, the pulsating got a lot better BUT ITS STILL THERE...  Did I get a rotor that is less warped than the one i was replacing but still warped nonetheless?  Anyway to find out what the heck I should do?  


Was thinking of bleeding but I don't think it would pulsate even if air in the line.  I'm stumped.

[SolidSnake3035]

See if there's any way that you can double check the integrity of the rotor.  Place it on an exceptionally flat surface.  If it appears to be straight/flat, then check to see if there's actually contact being made when the wheel is spinning.  Prop the bike up and spin the wheel around, be very thorough.

I don't actually know what I'm talking about but this seems like the obvious first step.

[uclabiker06]

Hm, well I really didn't want to take it off again but I guess I'll have to. As far as spinning the wheel I did that before I took it out for a test ride.  Doesn't seem like it was spinning freely.  Got about 2 spins before it would stop.  Rotor is definitely rubbing the pad.  I'll take it off and see if the other one is making the same rubbing sound.

[LA]

I got two new 5 hole Brembos. Never been on a bike. 

LA

[rockaduc]

Hm, well I really didn't want to take it off again but I guess I'll have to. As far as spinning the wheel I did that before I took it out for a test ride.  Doesn't seem like it was spinning freely.  Got about 2 spins before it would stop.  Rotor is definitely rubbing the pad.  I'll take it off and see if the other one is making the same rubbing sound.

You should def be able to get more than 2 revolutions on even a light spin of the wheel.  Maybe check the torque on the axle nut or check to see if the brake pads are retracting all the way after you release the brake lever.  If the pistons are sticking, they will put a lot of drag on the rotors.

[junior varsity]

My new rotors (ISR dampened) on the wheel removed the pulse I had previously felt at the lever. Also, they are lighter, look great, and really provide loads of stopping.

IMPORTANT NOTE:

With everything torqued to spec, you may not necessarily get a freely spinning wheel. Two reasons:

1) Brake pads/calipers are designed to constantly 'kiss' the rotor when not engaged. You don't pull the lever to move the pistons a distance before the pads contact the rotor. You grab some lever, you get some brake. The pistons just don't retract further than they need to.

2) If your speedometer is driven off the front wheel, as on older Monsters, you will be spinning a set of gears and the cable up to the speedometer. This is not a drag-free system by any means. The spinning wheel is slowed by the speedometer. Is this significant? Yes. To feel it, remove wheel, remove speedo-drive, and tinker with it in your fingers. When you are good and messy, re-grease and reinstall.

[Howie]

Make sure the buttons on the rotors can move, clean the friction surfaces on the rotors with a Scotchbrite and brake cleaner, sand glazing off pads and bed in brakes.

[stopintime]

Couldn't the pulsating be the other rotor? (having some built up hard spots?)
Howies advice should fix that, if that's what's going on.

Not an expert, but what about forks or axle bent/misaligned from the mishap?

[jerryz]

I has pulsing Brembo rotors  I converted them to fully floating and that cured the problem

[uclabiker06]

Um, yeah I don't know... kind of confused.  disc lock was on the right rotor and so that is the one i replaced but there is a lot of drag.  The lock hit the bottom of my calipers but i don't think it would have done anything to my forks.  I also re torqued the front wheel so its not that. We'll see how it goes

[erkishhorde]

Have you already ruled out a damaged caliper? When I took off w/ a wheel lock still on the rotor, the rotor was fine but I busted one of the mounting bolts for the brake caliper.

[uclabiker06]

Caliper mounting screws fit fine; nothing detectable by my eye.  Besides if it was the caliper I don't think I would get less pulsating after replacing the rotor.  Rotors float back/forth freely.

There is a little notch in the right side of the wheel axle and usually when I replace the wheel I put an allan or something in the notch to keep it in place but I didn't do that this time cuz I forgot. 

I figured since my forks aren't adjustable it wont matter if that notch is lined up or not.  Would not holding the notch in place while torquing the axle nut make a difference in my torque reading for the axle nut?  Just trying to think of all possible angles.... 

[Howie]

How you tightened the axle is not the problem, you are correct, the notch only matters on adjustable forks.  Did you clean the rotors with a Scotchbrite  pad and brake cleaner and deglaze the pads?   Small amounts of brake material transfer to the rotor.  Uneven transfer or brake materials that don't like each other can cause a pulsation.  Also, what is the condition of the rotor?  Is it excessively grooved?  Worn below limits?

[scott_araujo]

Make sure the buttons on the rotors can move, clean the friction surfaces on the rotors with a Scotchbrite and brake cleaner, sand glazing off pads and bed in brakes.

+1.  Completely solved my pulsing front brake problem.  It also greatly improved the braking performance.

Scott

[uclabiker06]

The rotor seems fine.  I'm not really good at using my micrometer but it seems fine.  Surface is flat to the touch so no grooves.  I think I am just going to bleed the brakes and instal a new pair of ferodo platinum pads that i got a while ago.  Maybe that will solve the rest of the pulsating issue.