On Feb 19, 2011, at 1:56 AM, CycloFiend wrote: > on 2/18/11 7:09 PM, rw1911 at rw1...@gmail.com wrote: >> I've recently installed Paul brakes (neo-retro front, touring rear) on >> my relatively new to me 700c All-Rounder. The rears are wonderful, if >> not too powerful... I can skid at will. However, I'm experiencing >> extreme shudder and fork flex on the front. >> >> The headset is tight and the pads are toe'd to contact forward. Under >> low to medium speed braking, I can see/feel the fork flex (a lot!) >> and shudder. The straddle cable is set at about the top third of the >> lower headset cup. I've cleaned the rim and while it has gotten >> slightly better with use, is this a matter of adjustment or is the neo- >> retro too powerful? > > > This has cropped up on CX boards (and maybe iBob - too late to skim the > archives there). The working theory (which seems pretty salient) is that > flex in the hanger tends causing the shuddering.
Flex in what hanger? Do you mean the one that connects the brake cable to the straddle wire? If so that's very likely to be a red herring IMHO. It's too small compared to the thickness of the metal to flex significantly. This is more or less typical in bikes with cantilevers and light road forks. It's one of the reasons that old MTBs with rigid forks had such big fork legs. The worst fork judder I ever saw was my friend Steve's Specialized S-Works from the early 90s; it had a really light road type fork and shook to beat the band on any braking at all. The bike weighed about 20 lbs but that was the tradeoff. My StumpJumper with suspension fork had no fork judder, but the fork was massive and there was a brake booster. Steve put a brake booster on his S-Works and it stopped the problem. The shudder is caused by stick-slip as the rim passes through the pads and the main issue there is fork flex (so long as the rim is clean and the pads are in good shape). Using a brake booster constrains the lateral motion of the cantilever studs as the fork flexes and stops the judder. On my 26" A/R I use a Nitto Mini front rack and that seems to stiffen things up enough that there is no fork judder under any kind of braking. I don't remember if there was any problem with this before I installed the rack, it's been on there about 10 years. My CX bike has some of this but it doesn't bother me enough to put a brake booster on it. The geometry of the brake itself, how much it flexes, how much play there is on the post, etc. are also likely to be contributors. To sum up my recommendations: 1. Clean the rim to make sure there are no sticky or slipper spots on the braking surface (the OP said that he did this). Also check the rim joint to make sure there is not a bump there which initiates the problem- if so, file the joint smooth. 2. Clean the surface of the brake pads with a file or sandpaper. Check toe-in to make sure this is correct. 3. Check to make sure the retaining bolts are properly tightened and that there is minimal play of the brake on the braze-on post (putting a thin washer between the bolt and the brake may be necessary- do not put it behind the brake, though- you don't want to move the brake away from the fork). 4. If those don't fix it, stiffen the front end with a brake booster or something like a Nitto Mini (if it fits) or a Mark's Rack. The Nitto Mini will be stiffer and more likely to be useful in this regard because of the way it mounts to the fork crown, but it may not fit the bike. Rivendell can advise. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
