Brake Centering Screw
 

Anybody ever had to replace one of these?

https://lh5.googleusercontent.com/_h...0/P5140010.JPG

The threads are fine but the hex cutout is stripped so I'll probably have to use some kind of extractor. The parts diagram calls it an "EC Bolt - M4x10.2" - that sounds like something I should be able to find at the hardware store.

http://bikeforums.net/attachment.php...hmentid=202012

http://www.totalbike.com/cgi-bin/sch...page=sh-br7700

I'm just looking for any advice - like do I need to put on my third hand tool or loosen the cable before I pull it out?

If you take the pressure off it by pressing down on the arm, you should be able to turn it out by jamming an old screwdriver into the hex.

You can probably match the thread, but not the shape of the head. If you can find it a stainless steel screw would be much more preferable.

BTW- if you ask at the LBS, odds are that eventually they'll replace a crash damaged brake from which the original part can be scavenged.

Thanks - I'd much rather have a screw head than a 3mm hex anyway. That thing rounded off way too easily.

It reduces the chances of damaging the heads if you take the load off before turning these. The same applies to derailleur limit screws.

I've never used the centering screws on any double pivot sidepull brakes, including a set of Dura Ace brakes just like the ones you picture. I adjust the rim clearance by setting the cable length and fine tuning it with the cable adjuster and I center the pads just by twisting the entire caliper by hand then tighten the brake nut fully. If the screws in my brakes fell out or stripped, I'd never miss them.

Maybe a set screw of the proper thread?

http://www.funrcboats.com/images/pro...etscrew_md.jpg

In my V brakes I use thumb screws like mcmaster 92552A426 (M3 in my case).

Makes it easy to adjust the brakes without tools.

I've had good luck finding that sort of thing at Fastenal stores, but can't you just order one from a Shimano dealer?

Actually, you would miss them, cause you used them every time you applied the brakes...

As centering screws, I agree they're stupidly redundant, because DPs are easily centred via the handy lever fixed to the main pivot bolt that's formed by the third bit of ally that's there to hang the side pivot from. As you say, centering is dead easy - I just put a thumb under the end of each caliper to hold them open against the cable and turn the brake around its mounting bolt, using my fingers to ensure most of the effort gets there.

But the bottom of the screw forms a fulcrum point where the high-leverage arm adds force to the centrally-pivoted one. I'd be interested to feel the difference eliminating this fulcrum would make... I suppose the brake would still kinda work.

Actually, I guess the adjustment might serve an aesthetic purpose; to allow the arms to line up across the top given different rim widths and pad thickness maybe.

I like the grub screws. You could fill the screw head recess with melted wax to tidy it up if you like... wax weighs less than steel ; )

Also, if you can't get any purchase on that screw with a slot screwdriver jammed in, I'd just disassemble the caliper and go from underneath with pliers until the screw head's exposed.

Well I find the stupidity useful. When switching wheels I have to adjust brakepad height for the different surfaces and then that messes up the centering... not by much mind, but I like 'em tight and that means the centering has to be spot on. The centering screw is a much quicker way to do it than the mounting bolt.

OK, good point, they do serve a purpose but ease of centering isn't a necessary one. I'm away from home but I will try to see what happens if I remove one entirely as soon as I can.

Not if you don't do up your mounting bolts needlessly tight. And don't talk to me about star washers... geez, leave em off. It doesn't take that much to hold your brake in place. If you can move the brakes but you have to mean it, that's about right. The only force acting to push it off-centre is via the cable housing.

I have a feeling the bit the screw goes through might act as the fulcrum then...

Right, something has to fill that function. I suppose the casting/forging could be redisigned to include a "bump" at that location or, better, a fixed steel insert pin. Maybe the screw was just a simple thing to use and the centering function was an afterthought.

"Maybe the screw was just a simple thing to use and the centering function was an afterthought." --HillRider

I suspect that this is most likely the reason, and I appreciate Shimano going the 'extra step'. I think dual pivot brakes are one of the better evolutionary engineering changes made to a bicycle component.

DiabloScott, It should be a little easier to remove if you operate the quick release and squeeze the arms together. I've never removed one, let us know how it goes.

Brad

I'm not sure about that; I'm having a hard time imagining why the brake shouldn't work at all without the fulcrum, but it might be the only way to check to grind off that part of the arm.