Interesting idea, it goes with my idea about "stealing" force from pressurizng the pads. Force required to compress the spring, compress the housing, stretch the cable, or overcome crud-based friction, does not result in compressing the pads on the rim.
Ken Freeman Ann Arbor, MI USA
-----Original Message----- From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of dddd Sent: Tuesday, October 24, 2006 2:49 AM To: Classic Rendezvous Subject: Re: [CR]Campy Gran Sport Brakes - any good ???
I've said it before, but have since verified repeatedly that relaxing the return springs on such calipers can make a huge improvement in braking power and also on the effective smoothness of the cables. As a mechanical engineer, I admit having previously underestimated the degree of improvement afforded by this modification. I only yesterday spruced up the brakes on my newly acquired 54cm, aqua blue-green, 1980 Peugeot PKN10E and the Weinmann 605 calipers now operate easily from even the tops of the hoods. I've done other Weinmann sidepulls, Campy and Suntour calipers with similar result and still have plenty of cable tension to keep the levers from ever rattling. I simply remove the caliper and twist the ends of the spring inwards. I try to bend the same amount inward on each end of the spring, preserving the aesthetic symmetry of the top of the mounted spring and bolt, and preventing either end of the spring ends from slipping past the spring stops. Usually the bend distance is just a few millimeters on each end, and I release the QR first, keeping the cable attached, and hold the caliper open to guage the amount of needed bend and correction bend. Takes but a minute with stout pliers. If the cable isn't installed and adjusted first, the amount of pre-load on the spring is impossible to guage. Also, the opposite end of the spring may tend to (painfully) slip past the spring stop on a wide-open caliper. Again, it almost seems almost like 3/4 of the effort needed to stop the bike comes from the springs, before this mod is performed. I also advise testing the installed calipers for over-tight pivots, another source of horrendous braking. Release the QR, then free one end of the spring from the stop. Without any spring tension, the pivot adjustment will be easy to quantify. I have often wasted good amounts of time trying to achieve lower braking effort by optimizing the cables when the problem really lied elsewhere. I feel a little stupid once the real problem is finally corrected, and the lesson re-learned: even un-lined cables can work quite well. Can anyone tell me which saddle and Simplex rear derailer are correct for the 1980 PKN10E Competition? Those G.S. brakes should work well on any bare-sidewall rim. Ano'd rim surfaces can cause multiple problems with some pads, and can be treacherous in the wet. FWIW, I've never felt the need to relax the springs on Shimano or Mafac calipers.
Auburn, CA usa
\r?\n> I put some Campy Gran Sport Brakes on my Italian Mystery bike.
\r?\n> They look good but couldn't stop much.
\r?\n> So I switched over to Kool Stop pads.
\r?\n> Now they stop a bit better, but I would not trust them in an emergency.
\r?\n> No such problem with old Mafacs or old Shimano side pulls.
\r?\n> What gives?