pearcem

Searched with no luck. The bike is a relatively new (500 miles) Raleigh Tamland with Spyre TRP brakes. I recently bought a new dedicated road wheel set, Stan's Grail Disc, and have put about 60 miles on them. I am using the same size and brand of rotors that came with the bike, the 160 mm TRPs. I also followed the exact same break in procedure that worked just fine on the original wheel set.

Now, I am having very bad brake shudder in the front only on the new wheels. It is bad enough that the fork visibly oscillates from front to back as the brakes grab and slip. It happens when I depress the lever to about the halfway point. It I am just riding the brakes lightly so that the pads make contact but are not slowing me noticeably, no issues. Once I hit about the half way point and the brakes really grab, the shudder starts, and can be felt throughout the bike, especially through the braking hood. It happens anytime I am going faster than 6-7 mph, and increases proportionally to the amount that I am squeezing the lever. Absolutely no issues with the rear brakes whatsoever.

I have cleaned the discs and pads with alcohol and disc brake cleaner. I have sanded and re-bedded the front disc and pad. I have re-centered the caliper, and checked that everything is tight throughout the whole brake assembly. Both pads appear to be striking the rotor at the same time.

Any ideas as to what the problem could be?

dabac

Check the headset adjustment.

pearcem

Headset seems to be fine, no noticeable play or wobble and there is not any excessive vibration or clunking. I should probably have clarified, I can actually see the disc slipping and grabbing as I come to a stop. No issues or new noises except when under moderate to heavy braking.

FBinNY 

Hub bearing play is the first thing that comes to mind. The other is that being new discs, their surface may not be even, or possibly the edges are within the pad area. When the puck overhangs the rotor, wear causes an overhanging edge. Then if the next disc isn't identical, or lined up identically in terms of concentricity, the overhanging edge causes problems.

As I think about it, pad overhang strikes me as very likely hence the bold.

pearcem

Thanks for the replies. I am a little new to the DIY bicycle mechanic work, so could you elaborate on how to check for those things? While the wheel is mounted in the dropout, there is no side to side play in the hub, but I am not sure if there are any other ways to check for that. With the brake locked onto the pads, it does not look like the pads overhang the rotor. They are fairly close, and I will admit it is a little hard to see, but if they do overhang, it's way less than 1 mm, and not discernible to the naked eye (unless there is a better way to check). I will remove the pads and see if there is any indication that there is uneven wear or some other pad issue. One thing I also just noticed that was a little odd: a few sections of the front rotor's exterior edge were very slightly rough. Almost like whatever machine milled them caught the blade a little bit. Unless there is some reason I shouldn't, I will sand those edges until they feel smooth to the hand when I take the pads off.

dkmatdrum

Spyre shudder
I have the Spyre brakes and 160mm rotors as well and they do the same thing. I thought it was a loose headset and took it to a shop and had them ride it. The verdict was that the pads are overhanging the spoke like lightening cutouts in the rotor and pulse as the pad traverses the area of the cutout. There is a wear pattern on the disc that shows this on the inner edge of the swept area.

dkmatdrum

Are rotors just rotors?

​Since the pads overlap the brake track because of the lightening cutouts can I just replace the rotor with one that has a wider track?

ghostgxz

thats what i would do

FBinNY 

Reading this, I brought up a photo of the brake. Assuming the rotor comes with the brake, the rotor shown has a very narrow brake track. Small holes and slots on the brake track are there to improving cooling (works on MC) and won't cause pulsing because they pass too fast. Also they're usually staggered so whatever pulsing might happen is many tiny ones per revolution and can't be felt.

OTOH the disc I saw has a track so narrow that it's highly likely that the puck will overhang to the inside and you'll feel the supporting spider arms sweep by causing a noticeable pulsing.

You might, (might, no assurance here) get some improvement if you use a Dremel to break the leading edges of of those arms, and other interrupted places so they can slide into the puck without bumping on the edge. Or look for replacement discs with a wider swept area so the pucks don't track over interruptions.

Looking ot some photos of rotors, I suspect that many designers are trying too hard to be cool, and putting style above function.

FBinNY 

Yes, within reason. You need to match the diameter (or move the brake) and find one with a brake track wide enough to address the issue.

If you can't find one with a track wide enough, look for a better angle of entry as the arms sweep through the shoes. Think slicing, not chopping.

dsbrantjr

"...if you use a Dremel to break the leading edges of of those arms..."

or possibly grind away some of the friction material at the edge so that it no longer overhangs. It might be easier to narrow the pads than to widen the rotor.

pearcem

Thanks for all the insight. This is a little odd since I have the same rotors on the old wheels and no problems, but I could definitely see the possibility of what you are talking about. The leading corners of the pads seem to be worn at a much faster rate than the rest of the pad, right about where they would hit the arms. I am going to try a few of the simpler solutions before my ride tomorrow, and if that doesn't work, I guess I will try a new rotor. Thanks again

FBinNY 

There's lot's of possibilities and subtle variations can make big differences.

For example, if the pucks are held rigidly and mostly on the continuous brake track, then they should stay flat and not dip into the interruptions. OTOH if there's some float or lack of rigidity, the puck will wobble into the gap, then bump the opposite wall. Think of the cutouts as potholes, and like real potholes, how you hit them and the speed determines how much impact there'll be when you hit the far lip.

One thing you might try, is moving the brake a bit so the pucks are better centered on the brake track, and see if that helps. If you get a change, then it's a question of dialing in the exact position where there's the least (or no) pulsing.

pearcem

Well, it's definitely happening on both front wheels now. It's much more noticeable on the newer set, but I think that might be because the 40 tires on the stock wheels are dampening the vibration a bit. I have tried:

Sanding and cleaning disc and pads
Re-centering Caliper
Re-mounting disc to make sure it was flush on the wheel
Tightening Headset
And taking a dremel to the portion of the arms that pass under the caliper

The last thing seemed like it might have made a difference. I sanded down the leading and trailing edge of the first couple of mm of the arms so that a sharp corner did not pass under the pads. The vibration is still there, but it seems like it has been dulled a bit. Unfortunately I can't really reposition the calipers without some washers, which I don't have. The weird thing is that there are still no problems on the rear brake with the same set up. I might play around with the caliper position a bit, or take it to the LBS and let them give it a go this week.

FBinNY 

The fact that grinding a "ramp" onto the leading edges made a difference is solid evidence that the pucks are deflecting into the gaps between the arms. Moving the caliper outward with some spacers (if possible at all) will improve that by getting the center of forces onto the non interrupted part of the rotor. Another alternative is to carefully note which area of the pucks are on solif ground, and which pass over the gaps, then grind or file away some material from the overhanging area so they don't touch at all. Note, that this approach will only work if the problem area is less than 20% or so. Otherwise the pucks will simply tilt for full contact nullifying your effort.


BTW- IMO (opinion only) having a rotor with inadequate wiping area width, so pucks pass over interruptions is (being as nice as I can) just plain dumb. Anyone with the least familiarity with brake operation should know that it will cause chatter. The rest is a matter of degree, but it's so easily avoidable.

pearcem

My thoughts as well. I am going to drop it off at my LBS and let them tinker a little (maintenance still covered). If I need to get some new rotors, that's fine, but I would rather them be able to do a little trial and error to make sure I get some that solve the problem.

I agree, that's not the smartest design for a set of brakes. As far as I can tell, the pads are large enough that no matter how I adjusted them, they would hang off the rotors on one side.