PunctualAlex

I recently got an old Novara Randonee touring bike, it has 27"x1 1/4 Araya 36H alloy rims laced to Suzue hubs and Shimano cantilever brakes. I put in the requisite few hours cleaning, repacking, and truing different bits of the bike because I had noticed a slight wobble in the front wheel that was causing the brakes to catch at one point on every rotation. After an hour of truing I've eliminated every wobble in the rim (I think) but the braking problem persists.
I noticed that it always catches at the point directly across from the valve stem which (I assume) is the seam of the rim. I don't have a set of calipers on hand, but is it conceivable that the rim is wider at the seam than elsewhere? At every rotation, this spot on the rim causes the front end to shudder with the force of braking, and (call me paranoid) I can't help but think that has to be pretty bad for a headset. Is there any risk of damaging the head tube, etc. during hard braking? This is a touring bike, so it's likely to be subjected to heavy braking loads over time.
Is there anything to be done about this? Could it be filed down with fine-grit sandpaper if it is indeed wider, or will this damage the rim?
Thanks for the help, everyone.

frankenmike 

Check very carefully that the rim doesn't have a crack at the wide spot. If not, just adjust the brakes so they don't rub. I wouldn't worry about damaging the headset. Don't sand the rims.

bkaapcke

Remove the tire when checking for cracks. Could be cracked on the inner layer and the tire pressure is spreading the rim out. bk

StephenH

Could you have hit a bump and just dinged it there?

enock111

The problem could be a dented rim from hitting something, a seem in the rim, or untrue (but you said you trued it for a long time. I wouldn't worry about it damaging the headset. I would just adjust the brakes so that they don't rub are are just a little less sensitive, if you cant live with unsensetive breaks then get a set of new 700c rims and they will work fine with n older frame.

DannoXYZ 

Take off the tyre and use some calipers to measure the width of the rim. Then slide the caliper all the way around the rim and verify that it's the same width all the way around. I suspect the wheel got a hard-impact and the sidewalls on the rim are flared outwards at some spots.

Either that or the seam of the rim doesn't line up just perfectly. That little lip that pokes out is a good source of metal splinters that'll get embedded in your pads and grind down the rest of the rim.

Mr. Underbridge

That lip should wear down pretty quickly, shouldn't it? That happened on a wheelset I bought recently - brake pads picked up some metal (presumably from the rather uneven lip that came on one of the wheels) and gouged a couple of lines in my rim before I could pry the metal bits out. It hasn't done it since the first week I owned the wheels, though, and the braking seems much better as well.

I can't imagine those 27" wheels are particularly new, but perhaps low miles?

zzyzx_xyzzy

If it's a problem with the brake pad catching the seam, you can try flipping the wheel over and see if it's better that way.

jcm

OP:

You say that the front end "shudders with the force of braking" and that the pads catch at that point. So, please try too refine this a little:

Is the sensation somewhat like a split-second snap - like passing over the seam, or is it a more lengthy modulation, like a whole section of the rim is rubbing through the pads?

Does this happen if you hand crank the bike in a stand, then brake the wheel? Or, just when you're riding it?

Check for a crack with a black permanent marker. Paint up the area, then wipe it down with Goof-Off. Don't soak it down or you will rinse out the ink from any crack. If there is a crack, some of the ink will remain in it and will be easier to see.

Remove the tire and slowly spin the wheel next to a straight-line opbject. Look for a bulge using the straight line as a sighting plane. Do both sides, mark the area and see if they are across from each other.

Does it occur with the tire off the rim?

TallRider

It's common, especially on old single-wall rims (that were the norm in the 27" world), for there to be a bulge at the rim seam, either wider or narrower. if it's big enough to feel while braking, you should also be able to feel it if you run your thumb and forefinger along the rim (pinching it lightly).
However, a slight bulge shouldn't be enough to cause major catching or shuddering, just slight rhythmic feeling.

cyccommute 

You would think but, in my experience, a bump at a seam never goes away completely. It's one of the reasons I prefer machined rims.

PunctualAlex

Right, thanks for the advice everyone- I haven't checked with the tire off yet, but I will before I take it out for another ride. As for the braking problem:

Just for a split second- as I said, I've trued the wheel as best I can and there's a very clear point at which the brakes catch.

This was actually how I figured it out. When the bike is in a stand and the front wheel is spinning, it's possible to squeeze the brake lever only slightly until the wheel begins to catch at this one point. There's an area about a thumb's width directly at the seam, or at least where I assume the seam is (it's impossible to see, but it's directly across from the valve stem). While this area is between the brake pads, it sticks. When this area slides out of the pads, it spins freely. Again, this "trouble patch" is only about a thumb's width.

I'll try that, thanks!

To try to respond to everyone else: The seam isn't out of alignment, or so it seems (sorry). The wheel is true. The brakes have been adjusted wide enough to eliminate brake rub and the wheel spins fine, there's just an annoying modulation in the braking just around the rim seam and I was concerned about damage to the headset or (gasp) ovalizing the headtube. I'll remove the tire and check for cracks on the inside of the rim, ink the seam, etc. etc. but failing that I'm willing to believe that the wheels (while old) are low mileage and that the bulge at the seam hasn't been worn down yet.

jcm

Okay, you've done your homework. It's just the seam slightly misaligned at manufacture. It's random variation in production. The very same rims built an hour later might not do it. I have rims that do that - maybe not to extent that it bothers me, but, like Cyccommute implies - you get what you pay for.

oldster

Are the bearings loose in the headset, and making any very slight ,"grab" seem much larger than it really is????

PunctualAlex

Nah, I checked first thing- the headset has plenty of grease, it's tight but not binding, and the races are set squarely in the head tube. I went to my friend's shop today, but I ended up rebuilding my road bike in anticipation of a stretch of nice weather instead. I'll check the wheel in question tomorrow.

Deanster04

My thoughts exactly. Make sure your head set isn't too loose. If you are getting a shudder then something is loose. If the rim is bent out you can use a C-clamp and carefully bend the rim lip back in place. The Araya should have a seam in the area you are describing. Turning the wheel around if the seam is the problem might help as well.... Good luck.