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Discussion Starter · #1 · (Edited)
I have a 00 stumper Pro, its got the original brake assemblies and brake mounting posts/bosses on it, Avid Mag. They seem like they have a lot of play in them.
I hold the top of the brake where the cable clamps down and i can move it about 1/8" or more back and fourth each way. Not the normal brake closing movement, but the opposite ways like the boss or the inside of the brake arms are wore out, I also can twist them a little bit too and theres play. I know they have at least 1500 miles on them, could be more.

Can I replace the posts/boss threaded into the frame? and inner brake parts? Any ideas guys?
 

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TMaster said:
I have a 00 stumper Pro, its got the original brake assemblies and brake mounting posts/bosses on it, Avid Mag. They seem like they have a lot of play in them.
I hold the top of the brake where the cable clamps down and i can move it about 1/8" or more back and fourth each way. Not the normal brake closing movement, but the opposite ways like the boss or the inside of the brake arms are wore out, I also can twist them a little bit too and theres play. I know they have at least 1500 miles on them, could be more.

Can I replace the posts/boss threaded into the frame? and inner brake parts? Any ideas guys?
My experience has always been that the bushings inside the brake arms themselves always wear and cause the problems you're having before the bosses on the frame (steel bosses versus brass bushings).

I'd say take the arms off and check for obvious play and check the bosses also for excessive scoring. You can replace the arm's by buying new brake's OR by checking into replacement bushings for your Mag's (I don't know if they exist or not and it may not even be worth it - $$$).

Not sure about your frame - I don't know if Spec uses replaceable bosses on that frame or not. You can tell by looking at the base of the bosses (with the arm's removed), just above the frame mount - if there are wrench flats then they are replaceable. Just make sure you match up the thread pitch so you don't crossthread and wreck your frame.
 

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Discussion Starter · #3 · (Edited)
Ok i took it all apart. The bosses are not true all around on their diameter. I have a set of calipers/micrometers I used to measure. THe Lowest point diameter is 7.92mm and the highest diameter is 8.00mm. The they are wore uneven.
The inserts on the brake are 8.20mm ID to 8.25mm ID. So im guessing they wore equally or didnt wear.
So were talking 0.33mm or .012" diametrical slop which seems too much to me.

The bosses are threaded into the little welded mount, So im pretty sure they can be replaced. I'll take one out and find some replacements.

 

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TMaster said:
Ok i took it all apart. The bosses are not true all around on their diameter. I have a set of calipers/micrometers I used to measure. THe Lowest point diameter is 7.92mm and the highest diameter is 8.00mm. The they are wore uneven.
The inserts on the brake are 8.20mm OD to 8.25mm OD. So im guessing they wore equally or didnt wear.
So were talking 0.33mm or .012" diametrical slop which seems too much to me.

The bosses are threaded into the little welded mount, So im pretty sure they can be replaced. I'll take one out and find some replacements.
I wouldn't put too much faith in measuring the OD of a roll formed boss. Finding 0.012" out-of-round isn't too surprising. If they were machined titanium or aluminum i'd be wondering, but what you have isn't much of a shock.

Do you have any means to check the ID of the brake arm bushings, perhaps some pin gauges or at least an 8mm dowel? I'd be paying much more attention to those. Remember the "steel versus brass" thing I mentioned earlier? I hope so.

Have you tried comparing your front brake's with your rear brake's?
 

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Discussion Starter · #5 ·
yeah i measured those, 8.20 to 8.25mm ID, sorry i put OD by mistake. The are pretty equall all around on the inside. They are steel i believe. so, again 7.92mm boss OD to a 8.25mm bushing ID.
 

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Discussion Starter · #6 ·
OK i measured the front brakes, they are in better shape on the bosses, pretty equal all around at 7.99 to 8.05mm They dont look wore at all. different metal i bet its a SID air fork. The bushings on the brakes are wore funny though. one side id towards the head of the bolt you put in; is 8.25mm and the bottom of the bushing where it seats on the boss is 8.10mm So its wore like a mofo. Time for new boss on the back and new brakes all around.
 

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TMaster said:
OK i measured the front brakes, they are in better shape on the bosses, pretty equal all around at 7.99 to 8.05mm They dont look wore at all. different metal i bet its a SID air fork. The bushings on the brakes are wore funny though. one side id towards the head of the bolt you put in; is 8.25mm and the bottom of the bushing where it seats on the boss is 8.10mm So its wore like a mofo. Time for new boss on the back and new brakes all around.
The real question.... is braking performance effected by this? my avids also have fair amount of play, but since they still function perfectly, I haven't let it bother me.:smilewinkgrin:
 

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the avid's i've had also have had similar inefficienes with the amount of play in the v-brake. I would be willing to bet its your brake and not the boss itself.

If you have another bike, put the avid's on there and i'm sure you'll get the same results. Its nothing really to worry about too much. They should work just as well.
 
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