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Old 10-17-10, 12:30 PM   #1
chico1st
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cant center brakes

hi i have these brakes.


I cant figure out how to centre them... what i do is release the quick release clamp the pads onto the rims and hold the front bolt (left most in picture) and tighten the rear bolt, standard nut behind the crown (not in picture).

but as soon as i pull the brakes it just goes back to the way it was... Ive watched videos but nothing seems to work.
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Old 10-17-10, 12:40 PM   #2
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Make sure your front wheel is centered properly. Is your wheel in the dropouts? Does the rim/tire have the same clearance on either side of the fork blades?
There are flats on the 'nut' that the brake spring passes through. A 13 or 15mm (or whatever size it is) cone wrench should fit on those flats.

You should be able to center the brake caliper by just moving it with the cone wrench. It is probably not necessary to release the QR, clamp pads on rims and etc. That seems too complex for what you need to do.

if you have been doing that, the brake arms may need to be re adjusted so they are not too loose or too tight. is there any side to side play in the brake arms?
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Old 10-17-10, 12:47 PM   #3
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^^^

The cable tension is the most likely culprit.
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Old 10-17-10, 01:58 PM   #4
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http://www.parktool.com/blog/repair-...-brake-service
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Old 10-17-10, 02:06 PM   #5
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Quote:
Originally Posted by chico1st View Post
hi i have these brakes.

I cant figure out how to centre them... what i do is release the quick release clamp the pads onto the rims and hold the front bolt (left most in picture) and tighten the rear bolt, standard nut behind the crown (not in picture).

but as soon as i pull the brakes it just goes back to the way it was... Ive watched videos but nothing seems to work.
Those are old Shimano single-pivot brakes. They were always evil to get and keep centered on the wheel.

What you're doing isn't going to work because you're not turning the spring mount after the brake is tightened down. The spring mount is between the caliper arms and fork crown in your photo. As Mr. Orange says- you can reach the hex on the spring mount with a cone wrench and turn it, but only after you've got the center bolt snugged down. Turn it until the brake shoes are centered on the rim, squeeze the brake a couple times, center again, and keep going until it stays where you put it.

If you can't reach the brake mount with a cone wrench, you can sometimes turn the bolt by putting a wrench on both ends of the bolt and turning the whole assembly. This works sometimes, other times the caliper adjustment tightens down and the caliper binds up. Annoying. The last ditch method is to take a round punch and hammer on the return spring to get the spring mount to move. This usually works, but it also tends to damage the return spring.
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Old 10-17-10, 02:33 PM   #6
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need a wrench holding on the side the brake is on ,
while you tighten the nut holding the brake on the fork on the opposite side.
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Old 10-17-10, 03:17 PM   #7
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Yeah, you cannot hold the brake by hand when tightening the nut, because you're only holding the arms, which will still let the centrebolt spin. You can hold the centrebolt with a 13mm cone-wrench. In most cases, you will still need to re-adjust the centering after you've tightened down the back nut. Insert 13mm cone-wrench and twist the centrebolt:

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Old 10-17-10, 06:29 PM   #8
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wow that was easy, i've always just clamped down the pads and everything was peachy... oh well... lesson learned
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Old 10-18-10, 02:36 PM   #9
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I've got the Park tools offset wrench, but I've found the old-school method more reliable for centering single-pivot calipers. It also works on all brakes of such type (the Park tools wrench doesn't always fit on the spring mount well enough):

(1) Tighten the mounting bolt nut on the back of the fork as tight as possible with the brake centered as well as you can get it as you tighten the nut;

(2) immobilize the front wheel by straddling it and holding it between your legs so that you're facing the front of the bike head tube;

(2) hold a flathead screwdriver or punch against the top of the spring on the side of the brake furthest from center. Hold it at an angle pointing down and slightly inwards, on or near the spring's coil;

(3) keeping the punch in contact with the spring, take a sharp whack at the top of the punch/screwdriver with a hammer.

This should shift the brake a bit more towards center. If it doesn't move, try the above procedure again. Repeat until the brake has swiveled a bit closer to center. Test the brake by pulling on the lever after every move to see if it remains centered. You may have to whack the brake so it actually moves past center, but then returns to center after pulling on the lever.

Two things to note when doing this: (a) take care to hit only the spring of the brake caliper. This part is steel and under tension at the coil, so the impact from the punch won't damage it, but if you hit the brake arm by accident, its soft metal will most certainly get dented or injured by the harder steel of a punch or screwdriver; (b) the pads do not need to be perfectly centered around the rim to be effective: the most important thing is that they are not rubbing against either side of the rim when the wheel is spinning freely. (Once one pad hits the rim, continued pressure from the cable will cause the other arm to swing to the rim faster, thus leading to an equalization of the brake pressure from both sides).
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Old 10-18-10, 03:25 PM   #10
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You can also use a BB cup spanner in the two coils of the spring.
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Old 10-18-10, 05:41 PM   #11
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You can also use a BB cup spanner in the two coils of the spring.
Clever. I've never heard of that. I'll try it next time.

Meanwhile, I've been tapping the stronger side with a hammer and punch, and it has worked reliably for me for many years.
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Old 10-18-10, 05:41 PM   #12
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Originally Posted by Jeff Wills View Post
Those are old Shimano single-pivot brakes. They were always evil to get and keep centered on the wheel.
It looks to me like the bolt has flats for a cone wrench, and that there's probably enough clearance for the cone wrench to get past the lower cup:


If you have clearance problems with the cup, remove the brake and add a washer to move the flats further out to where you can grab them with the cone wrench. Once you're at that point the rest is easy.

Last edited by JohnDThompson; 10-18-10 at 05:48 PM.
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