I spent most of the morning doing a search about front rotor/brake issues. Lots of info, but I still need to ask a question.

I noticed recently the Hawk exhibiting the classic "front end pulsation must be warped rotor(s)" symptoms. If you jump on the front brakes at higher speeds you can feel the front end shake, and if you look down the fork tubes I can see the front wheel doing a front to back motion. At lower speeds you can feel a release/pressure/release/pressure sensation. All things point to the rotors.

Here's the interesting part. The bike has about 26,000 on it. I wanted to overhaul the front end anyway, so I ordered all the stuff I needed. New fork guide and slider bushings, fork seals and dust covers, fork oil, tapered steering head bearings, new brake pads, etc.

Before I tore it down I built a steel plate that bolts where the caliper bolts. Remove the calipers and installed the plate. Put the dial indicators on and checked runout both sides. Left rotor has .002", right rotor .005" runout. Manual calls for a max runout of .012". I'm under.

Rebuilt the front end, removed the Metzler M-1s, put on a set of
M-3s, and rechecked the runout numbers. Same numbers as before. Still very much the same at high speed. Maybe a little less or non-existent low speed pulse. I put about 100 miles on so far.

Runout has been checked at the furthest inside and outside points of the rotor since the middle is hard to check without the holes in the rotor wanting to interfere. The left rotor is a slow movement several times per one wheel rotation from .000 to .002. The right rotor is one swing per wheel rotation from .000 to .005 and back to .000.

I'm considering building a brake pad blockoff plate so I can run the bike with one caliper off the rotor and the plate inbetween the pads. This would allow me to ride it and brake with one caliper active at a time. This way I could isolate which rotor is causing the problem, if either. It's just interesting I'm under the max runout but experiencing what I believe is a rotor problem.

The question:
Anyone had this from a rotor that was under the max runout limit?

I've been eyeballing the rotors on the F3. It's a 96. They look close to the same as the Hawk, but I don't know if they would work as a temporary swap to see if they would cure anything.

 

how about wheel bearing ? & check front axle runout ???

does sound like the classic warp'd rotor.

tim

 

Yes the F3 should work as well as VFR's from 94-present (slightly different carrier designs).

You might want to look at the pads. I've heard they can warp or wear poorly causing vibrations.

 

Pads are new when I overhauled the front end.

If the F3 rotors will work I may swap them on one at a time and see what I find.

 

That little runout should not cause any issues at all. I had the same problem on my XX and it turned out to be an out of balance front tire.

 

There's a good chance you have uneven distribution of pad material on the rotors. This will cause one or more areas to have more friction than the rest. The best way to get rid of this is sandblasting, but they can also be wet-sanded using a 120 grit and a strong detergent such as Dawn with water.

 

Have you checked the "rivets" that make the rotor semi-floating? If some of those are stuck you get the symptoms you described. Rotate them with pliers and blast dirt out with compressed air.

 

I did the rotate/spray with brake cleaner and no difference. I'm going to swap to my F3 rotors, which I don't have any probelms with, and see what happens.

 

And? And?

Is there an end to this story or what?

I'm experiencing the same warped feeling, especially at low speed when coming to a stop. So F3 rotors bolt to 'Hawk wheels? Cause I'm about to just get some new wheels while I'm at it for the track.

 

My guess is that you weren't measuring them in the right spot. It's really difficult to get accurate measurements on the bike, even though your setup seems nice. Mine was doing the same thing before my front end swap - one rotor had .015 runout. I think even at .012 you would notice that something isn't right.

 

I decided to wait until near the end of season and do the F3 wheel swap. That way I'll know what needs to be done this winter.

There's not much area to measure off of with a dial indicator. The holes in the rotor make most of the area useless as far as finding a spot to turn the wheel without the button on the indicator wanting to drop into a hole.

 

I'd say it's very likely to be the rotor going 0-.005"-0 that would give you noticable pulses... I think mine was .008" or so, but the symptoms where the same...