Positron400

Heya,

i have a set of tubular rims from the 70ties, which i recently taped new challenge tubular tyres onto. I use those in conjunction with Sora brake calippers (brake pads are fairly new and not really worn). However, whenever I decend, I get brake stutter/wheel shudder which doesnt inpsire me with confidence. My LBS reccomended i clean the rims to remove resudual glue from previous tubulars, which they say, is the cause of my issues when braking.
1.) Is this a reasonable cause?
2.) What should i clean my rims with, since I don't want to dissolve the taped tubulars and risk rolling them off the rim.

thanks!

choddo

What type of brakes are they? I’ve had horrible shudder from cantis before.
edit: ah you did say. Ok it’s not that then.

I wouldn’t think cleaning the braking track with isopropyl alcohol for example would affect the tyre adhesive on the rim.

Kontact 

Mariposa is a gel you apply and leave on overnight that does a very good job of removing tubular glue, and isn't oily or likely to migrate.

You could try acetone (nail polish remover), but I doubt it will do much.

Otherwise, try increasing your brake pad toe-in and ride down some safe hills until the shudder decreases.

Andrew R Stewart 

Yes, sew up glue left on the brake track can and does cause braking issues and is a sign of a newbie. Having said that and having mounted dozens of sew ups it is easy to messy up the brake track. But cleaning the glue off isn't too hard either, I use various solvents depending on what's on hand and find the sooner the glue is removed the easier it is to clean.

But other issues could also be in play. Kontact mentioned brake pad contact with the rim (roe in). If the caliper arm pivots are sloppy when the pad contacts the rim it will pull the caliper arm too and any pivot slop will let the arm wiggle fore and aft as you apply and release the brake. Then there's the rim itself. The sew up rims of 1970s were often so light (thin walled extrusions) so that with the tension of each spoke the rim would slightly deform and bulge outward. So a 36 spoke rim might have 36 little spots that are wider than the rest of the rim. Usually viewed as 36 points on each brake track that have more wear. Andy

Positron400

When i put on them tubulars, i cba to use glue, so i taped them with TUFO tape. I presume, previous glue jobs have contributed to the irregularities on the brake track.
Will give the toe in a try first and see if that helps somewhat.

SJX426 

I vote for cleaning the rims. I have noticed significant improvement after a good cleaning.

An example of what ARS pointed out. That did not contribute to shuddering on those wheels, GL330 rim.
P9201318 by Patrick Boulden, on Flickr

FBinNY 

+1 for glue as the culprit. Even if you don't clean with solvent, the problem self cures on its own fairly quickly.

I never bothered cleaning, and never had issues, though (after the first few disasters) never got much glue on the rims.

The slightly wider areas we used to see at the spoke holes of light rims, don't cause problems with braking because the frequency is too high, at over 100hz.

BTW, the stuttering you're seeing is a great detector for slightly loose headsets, so make sure that isn't compounding the problem.

spclark 

Good calls both.

When I got back into cycling earlier this year I had to update the glue holding one tire to its rim (from maybe 15 years ago? It'd turned to dust...) so I tried a trick I'd never before heard of: use paint masking tape to cover the rims' braking surfaces before applying that new glue. Takes about five or six minutes a side but vastly speeds application of glue as it's not so tedious an operation trying to keep it away from the sides. Once you're ready to mount a tire, simply peel away the tape then proceed as otherwise.

I've not noted any residue from the tape's adhesive affecting my braking performance either but as a caution I did wipe the braking surfaces with denatured alcohol on a microfiber towel before I climbed aboard again.

On a related note I've always used lacquer thinner to soften and dissolve old tire glue. New addition to my kit is augmenting its solvent effect with Scotchbrite non-woven abrasive where before I'd simply used 'elbow grease' to pick up the gunk. Makes fast work of what before had been a smelly, laborious operation.

Positron400

Thanks for the suggestions - I can exclude a loose headset as a culprit since i used the same wheeset in 2 different frames, and both exhibit the same shuddering issues. Headset is definitely tight.
So far, the issue hasn't cured itself over 400km. Will add pics of the rims for better root cause analysis

Kontact 

Not seeing any glue on the brake track...

Paul Waque 

Sometimes there is is an uneven braking surface at the rim joint.

Positron400

would that mean, i'd have to live with the shudder?

Paul Waque 

I am not aware of a solution for an uneven rim, but you should be able to observe if this is the issue by spinning the whes and lightly applying the brakes to find where the rim is catching.

DiabloScott

It might mean that the rim is worn out. The brake track gets thin but the joint doesn't.


Zoom in on this and you can see how the anodize has worn off near the spokes but remains dark in between the spokes; not what I would've expected. I think this was a GL330.

ljsense

With old 70s rims that look like bare alloy and have been glued who knows how many times in the past, the brake track may now just have sections that are smoother or stickier -- whether it's from old glue burnished in, oxidation, embedded brake pad material, stray grease and other lubricants, or the devil knows what else.

I'd use acetone and 000 steel wool and go over your brake tracks. Some acetone touching the rim/tire seam won't ruin your glue job or cause your tires to fall off next time you take a corner.

Then I'd get on the bike and brake like you do when you bed in new disc brakes -- go down a hill or get going fast, apply brake on one wheel for 5-10 seconds without locking up or stopping. Then do the other wheel, same way, repeat each wheel 5-10 times. That should smear some brake pad material across your rims as evenly as possible.

Iride01 

Brake pads seem to be sitting just high enough to press over onto the upper edge of the rim where the glue is. Might try lowering them a tad. Even if you don't think so, then just try it to see if that's where the cause is. Clean the pads and brake track again before testing it out.

From the pic, some might be right that maybe the braking surface on the rim is getting beyond it's time. But might just be the lighting, pic angle and stuff that might be smeared thin on the rim. Maybe the glue!

FBinNY 

The key to diagnosing shudder (and most other similar issues) is frequency.
A brake shudder synchronous with wheel speed, would indicate one problem spot of the rim, like a joint, bulge, burr, or sticky spot. OTOH a random shudder, especially one that tends to occur within specific braking conditions, ie. only when slowing, but not during hard stops, indicates a harmonic issue, usually related to brake arm flex.

When you apply brakes, the rim pushes the shoes forward. This imparts a torque within the arm, bringing the toes out, and letting the rear corner to dig in (think new chalk on the blackboard (if you're over 40 or so)). So brakes will often shudder under moderate braking, but higher brake force presses the shoes flat curing the shudder.

I'm not a fan of toeing shoes out more than what naturally happens with wear, and prefer to use a rasp to chamfer the rear corners of the shoes. The OP should also check for any play at the pivots, as this is often a cause of shudder.

My earlier reference to headset play wasn't as a cause of shudder, but instead as something that amplifies the effect.

.

grumpus

Denatured alcohol and steel wool - I think acetone might be a bit too aggressive.