jimmuller 

I have a rim (front wheel, a Sun 27" M-13II) which was made poorly. The two sections don't line up well at the joint. As a result one edge sticks up above the other and on one side of the rim it catches on the brake pad. I've tried polishing it down and have made it better but it still isn't perfect. Even after I've cleaned the surface it seems to get worse as I ride, as if pad material were building up on the braking surface.

Bombing down switchbacks at 30+ mph on Cadillac Mt. in Acadia Natl Park this past week made me realize how problematic the seriously thumping front brake could be. I gotta' fix this!

I can try polishing it more with special emphasis on getting the surface smooth as opposed to just lining up the two surfaces on opposite sides of the joint. Of course it will end with a slight depression in the surface, even more than it already has. Or I can simply buy a new rim and rebuild the wheel.

Have any of you ever tackled a problem like this? Is it possible to fix, or should I just get a new rim and be done with it? (Yes, I can build the wheel.)

I thought about whether to post this in C&V or mechanics, decided it was a virtually-old rim on a truly old bike, so C&V it should be.

Last year I posted a thread about the trouble I had getting new wheels built. I'm now down to this last unsolved problem. For various reasons I can't go back to the store who sold me this rim and who built not what I wanted and who screwed up a few other features. Long story, not worth repeating. But I'm just going to build all my own wheels from now on.

And for what it's worth - two loops around the Park Loop Road plus one run up and down Cadillac - 45.6 miles, 3440ft elevation gain. Got lots of attention for the "beautiful old bike", my Raleigh Gran Sport.

Mileage + age of bike + age of rider + elevation gain (in 100's of ft) = 180!

auchencrow

I think I'd attack that one with my orbital sander - that is, provided the step is no more than 20 thou or so.*
If it was worse than that likely I'd just replace the rim.

(*Such surgery would have to be done on the laced-up, tensioned wheel - the joint may sit a little differently as a raw rim.)

rich rice

I'd try smoothing it down with some 320 grit wet-or-dry sandpaper on a block, then go to finer grits to polish it back to a nice shiny finish. Just try to get it to be as smooth and even a transition as you can without creating a low spot. Most times this will work with satisfactory results.

bigbossman 

Let me get this straight - you're "Bombing down switchbacks at 30+ mph" on a front wheel that you know is defective?

Yikes.

Ever see what happens when a front wheel fails at speed? Don't try to "fix" it - get a new rim and rebuild.

3alarmer 

Yeah, what he said ^^^^^^^^^^

Or possibly:

rich rice

It doesn't sound that serious to me from the OP. If it is really out of whack, then obviously destroy it. If it is a matter of a sloppy joint but it's solid, it simply needs to be dressed with a sanding block and polished out. None of us can see it, feel it, or ride it. I'm not so quick to trash a wheel over something that I can adjust. Only the OP can decide if a correction will be safe. Then again, I ride on 40+ year old wheels all the time...

rootboy 

I had to do exactly as rich rice said Jim, on the very same model rim. Worked fine. Try to concentrate on the "high side" with the sand paper first, necking it down to the lower surface, then smooth out the whole braking surface to about 3 to 4 inches either side of the joint. As I remember I started with 220 grit and went up from there, to maybe 400 grit, to match the scratch pattern on the braking surfaces. Easier to do, of course, with no tire mounted. I'm picking up another pair of these rims from the LBS this week, and this reminds me to carefully check the joints before I pay, thanks.

jimmuller 

Thanks for the concern, bbm, but you got it backwards. Bombing down the switchbacks wasn't a problem. NOT bombing down was the problem!

Switchback? What switchback?



Here is the rim joint in question:

southpawboston

There's a thread going on right now on the CR list about this exact question. The response from JP Weigle was that back in the day, this was never cause for getting rid of the rim. Filing the weld down smooth to get rid of the brake thump was something riders just did as part of tuning their machines. Coming from JP Weigle, I'd put stock in it. Keep the rim and just try filing it down smooth, as some others have suggested.

fender1

If it were me, I would replace it. $30 is not that much if you re-do the wheel yourself. Also save the old rim and "work" on it if you feel you need too but I would feel that if a rim got out of the factory with this kind of defect, there maybe additional unseen issues. Per what Weigle said above, this is not the era when alloy rims are super expensive and some what high tech.

https://www.comcycle-usa.com/ProductInfo.aspx?id=6389740

Andycapp

If the rim were reversed, it wouldn't "cure" the problem, but would it reduce it? The brake pad would " fall" off the edge instead of catching it. Just an idea, I'd still try to smooth it out as well as I could.
-Andy

rhm

I would just attack it with a fine, clean, flat file. There's a small triangular area, maybe an inch long, that need to come down a little bit. After one or two swipes with the file, clean the aluminum crud out of the file before taking another swipe. Then fine sandpaper, mostly to see what it feels like. For best results, remove the tire/tube before filing; if lazy (I'm lazy), just let the air out and flop the tire over to the other side while filing.

I like Andy's idea of reversing the wheel; but what does the other side of the join look like? It may be exactly the same, in which case reversing the wheel will not change anything.

jimmuller 

Such a plethora of answers! Thanks all.

Flipping the wheel would just make the other side catch, since the two "halves" are offset from each other. Flipping the wheel would also earn me the wrath of the C&V style gods who insist that both tire label and wheel label be readable from the drive side. Can't have that, can we?

In any case, I have previously tried cleaning it and have already sanded it down quite a bit from the original. If I could make it stop building up rubber so quickly it might just be okay. But what the heck, a new rim isn't so expensive either. It's my time either way.

3alarmer 

If you are dead set on smoothing/filing this as a fix, try the
sandpaper on the brake blocks method and see if it gets you
anywhere after some riding and squeezing.

Start as coarse as you're comfortable and go finer as desired. YMMV

rootboy 

I solved that problem. I removed the stickers from my M13's, thinking they were ugly and non-C&V looking. Update; just picked my second set of these rims from the bike shop (I like these rims ) and the joint is a whole lot better on this pair ...though the polish is not as good on this set. Whaah!

jimmuller 

I've now spent some considerable amount of time sanding both sides of this wheel. I haven't taken either side down so far that the weld joint disappeared but it is starting to on both sides. After the first go at it yesterday I rolled the bike slowly past that spot with the brake applied lightly/ It seemed to grab slightly as if the rim were wider there. Rode it around the block and observed not only that it thumped but that it quickly built up pad material there.

I believe what is going on is that the rim is effectively wider right at the joint. The leading edge of one side's pad is pressing against the part sticking out on that side while the trailing side of the other pad is pressing against the part sticking out on the trailing side. Also the buffing may have left it with a slightly rougher surface causing it to accumulate pad material.

So today I spent more time hitting it with 600, with an emphasis on both further taking down the high side and smoothing out the finish before and after the joint. It feels nicer now but I haven't had a chance to ride it. It's been raining all day... I'm in bike withdrawal already.

photogravity

Yes, though my solution would be to put a drum brake hub on the bicycle. In all seriousness though, the answers others are offering make perfect sense and would be similar to the approach I would take with this kind of issue.

rootboy 

It can be a real chore Jim. I worked on mine a while. Someone suggested a flat file and I think if I had to do over again I would have started with a very fine file. Remove material fast, get it flat, then bring the scratch pattern back with various grits of sand paper. That bump you describe is troublesome however. Rim extrusion could have been deformed during manufacturing and that might be very difficult to get perfectly flat. Also, if you haven't done it, I would sure remove the tire and work on it. Do you have a very fine smooth file?

rich rice

Sounds like you're gaining on it. If it's too bad, then a new rim is in order. I should have prefaced my initial post with the fact that I build custom guitars for a living, thus have loads of experience at making problems go away, many long hours of hand sanding/shaping/smoothing/finishing every week, and plenty of very fine tools with which I can attack this sort of problem. However, a bulge is different, insofar as there could be structural problems. Most likely not, but you don't want to weaken the rim- just smooth it out. A very slight bulge would be insignificant, but a hefty one would require the removal of too much material, thus weakening the rim. It would be a good idea to measure the width of the rim in several spots with a digital caliper, to make sure you know what your target is. A brand new fine toothed flat file would be fine for leveling the surface, but be sure to only file in the cutting direction and have a file cleaning brush on hand to constantly keep the file immaculate. I would end up polishing the rim (once it is flush and level) down to about 2000 grit wetsand paper, then use a polishing compound such as Meguiar's No.9 Swirl remover to bring it to full mirror finish. Another step would be to use even finer MicroMesh before the compound, up to about 12,000 grit.

rootboy 

Sage advice Rich. I will detour a bit from your good advice to say that the Sun M 13 sidewalls aren't polished. The rims are but the sidewalls seem to be about 400-500 grit. I matched mine up pretty well going to 500 is all. Good caution on the bump, though.

rich rice

From the pics I don't think it looks too bad, I'd keep riding the rim- but my wife thinks I'm nuts.. probably some merit to her thoughts.

I'm not familiar with Sun rims, although I have a set on my Bottecchia. Guess I'll have to go out and see what they look like, and what model they are.. They were on the bike when I bought it, and I haven't done any serious work on it yet. Just a few rides, which convinced me I love the bike..

wahoonc

Got a set of calipers? Measure the amount of the bump compared to some other areas on the rim. I have ground down my fair share of rims over the years. On some bikes I just don't bother, on go fast road bikes or tour bikes I do. This is a measurement that I take when I buy a new set of rims. Some can be ground down some can't, I consider one with an excessive bump or edge to be a manufacturing defect. If the wheel is getting hub brakes I don't worry about it.

Aaron

jimmuller 

I thank you all for your replies. The brake bump I spoke of is attributable, I believe, to the offset between leading and trailing halves of the weld.



The offset from one side to the other creates a momentarily wider rim between the leading part of one side's brake pad at the trailing part of the other side's pad. Even when the ridge has been smoothed down to a mere ripple the widening effect remains.

I've been working on it and am quite certain it will be just fine eventually. All it needs is sufficient patience, beer, elbow grease, more patience, some test riding (long after the beer is finished), more beer, and perhaps more patience.

I'd ridden this wheel 76 miles a few weeks earlier and while it wasn't smooth braking it wasn't terribly thumpy either. The run down Cadillac is what made me decide to address the problem. I have no desire to cheat death again, even if it really wasn't much of a cheat the first time.