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Park Tool OBW 3 doesn't fit mah brakes?

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Park Tool OBW 3 doesn't fit mah brakes?

Old 07-17-21, 05:29 PM
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Park Tool OBW 3 doesn't fit mah brakes?

So I ordered the OBW-3 to use on my 1980's Shimano 600 side pull single pivot calipers and the took doesn't fit in 2 ways. A) in the front, the headset keeps the wrench from getting down behind the brakes to really get seated, and 2) The nubs on the wrench are too wide for the springs on the back of the calipers. Is this normal? Is there another tool that is more narrow? Will this tool only work on some older brakes?
I've included a few pics below showing.
The first is how it won't even get into a useful position.
The 2nd is showing where the other nub ends up far outside the spring coil when the other nub is full seated in the other spring. There's no way it fits.


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Old 07-17-21, 05:55 PM
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Wrong tool for this job. Shimano calipers that use this version of the center bolt (where the slop between the arms are set and locked by the threaded pieces behind the arms) are usually centered by a wrench (5mm in this case) that holds and rotates the center bolt from the front. As long as the two threaded pieces (one holds the spring the other is usually notched about it's circumference) are well tightened against each other (and the arms' slop/free movement is set) the speing will track the center bolt's rotation. It's the spring's position that brings the pads back away from the rim. The pictured tool does sort of work for the other type of centerbolt and spring (like DC or Weinmann and dozens of cheap calipers use). Andy
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Old 07-17-21, 07:51 PM
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Well good thing the wrench was only $8, heh

I've used two 5mm hex to turn the front bolt to center, and then hold in place while tightening the back bolt through the fork - but it still often seems to dislocate anyway no matter how much I tighten them.
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Old 07-17-21, 08:35 PM
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I can't tell by the photos if the caliper has a star washer between the last threaded piece (with the sort of knurling about it's edge) and the fork face. Brake star washers are not the flimsy lock washers that hardware stores sell but a thick (about 2 to 3mm) one with a star pattern embossed into it. Also the way the cable casing is done can act as a spring, trying to push/pull the caliper off center. Recessed center bolt nuts have a lot of contact area with the frame/fork and thus a lot of friction. I often place a small drop of TriFlow on the nut's insides and outsides. Andy
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Old 07-18-21, 05:32 AM
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Originally Posted by Andrew R Stewart
I can't tell by the photos if the caliper has a star washer between the last threaded piece (with the sort of knurling about it's edge) and the fork face. Brake star washers are not the flimsy lock washers that hardware stores sell but a thick (about 2 to 3mm) one with a star pattern embossed into it.
And front calipers will often have two such star washers, to provide wrench clearance from the headset cups.
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