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Replacing broken V-brake pivot axle
#1
[attachment=2970]

HARO BMX frame. One of the rear V-brake axles has broken off. Soaked with oil and heated, then tried to extract it with an easy-out, but no joy. Does the axle thread into the frame mount? HELP? Sorry for bad photo. Thanks. Chris.
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#2
Correction. NOT V-brake. The pivot axles are for Dual-Pivot brakes. Sorry.
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#3
Or maybe cantilever? Sorry.
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#4
Post a picture of your entire brake set, so we can help you fixing it!
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#5
Not sure but machining it out may work if replaced with a same size that broke off?!?!?!? But as bob said try to get a pic of the entire make up of the brakes.
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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#6
Brake bosses are threaded M10 x 1.

The pictures shows the boss broke off. The plate with three little holes is welded to the bike, and is not attached to the boss.

I would grind some flats on the post, clamp some big vice grips to the post to act as heat sink, heat the area up with a torch, and crank on the vice grips - wear gloves.

The bosses are common to both V-brakes, Cantis and U-brakes.
Nigel
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#7
As another reply said, the brake boss is welded to the frame. This frame needs to go to a framebuilder for repair, assuming that it is worth the expense. A very clever framebuilder might be able to braze a new post into the brake boss but the entire boss probably will need to be replaced. As the frame appears to be chromed, that poses other issues yet because the chroming will no longer be continuous.

(01-16-2012, 04:39 AM)roys101 Wrote:  HARO BMX frame. One of the rear V-brake axles has broken off. Soaked with oil and heated, then tried to extract it with an easy-out, but no joy. Does the axle thread into the frame mount? HELP? Sorry for bad photo. Thanks. Chris.
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#8
(02-04-2012, 04:01 AM)sheldonsite Wrote:  As another reply said, the brake boss is welded to the frame. This frame needs to go to a framebuilder for repair, assuming that it is worth the expense. A very clever framebuilder might be able to braze a new post into the brake boss but the entire boss probably will need to be replaced. As the frame appears to be chromed, that poses other issues yet because the chroming will no longer be continuous.

The above information is NOT correct. Post is threaded into the boss.
Nigel
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#9
The part you need, after removing the old post is:
http://problemsolversbike.com/products/cantilever_stud/

[attachment=3052]
Nigel
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#10
Ye rusted parts are tough to remove. You are in England?

You said you tried easy out. Soak with penetrant overnight if you can heat outside with a small pencil flame (wipe penetrant off first) give it a few sharp taps while soaking than try easy out again.

Since to use easy out you had to pre-drill it , use larger drill bit just a bit smaller than the bolt and carefully and straight drill again. This will leave you with a thin metal shell that you can than collapse and work out. Do pre soak for this too. Careful with the threads.

Take it to a machine shop.

I am including a copy of post I posted while back on penetrating oil test.

Machinist's Workshop magazine actually tested penetrants for break
out torque on rusted nuts. Significant results! They arranged a subjective
test of all the popular penetrants with the control being the torque
required to remove the nut from a "scientifically rusted" environment.

Type of penetrating oil ..... Average load

None ................................ 516 pounds

WD-40 ............................ 238 pounds

PB Blaster .......................214 pounds

Liquid Wrench .............. 127 pounds

Kano Kroil .................... 106 pounds

ATF-Acetone mix......... 53 pounds

The ATF-Acetone mix was a "home brew" mix of 50 - 50 automatic
transmission fluid and acetone.

Note the "home brew" was better than any commercial product in this
one particular test.
Never Give Up!!!
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#11
BTW be very careful not to break the easy out as than you will have a hardened metal shank stuck in there making it very difficult to drill.
Never Give Up!!!
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#12
RE: Nigel.

This particular V-brake boss is not threaded in place. The image you included is designed for aluminum frames and some forks with removable bosses. Steel frames rarely offer this luxury.

The OP needs to take this frame to a frame builder for replacement. The particular stud is TIG welded on. A replacement could be TIG'd or brazed into place, once all remnants of the brake boss have been removed. Another hurdle will be the chrome plating of the frame. Chrome releases toxic fumes if TIG welded or brazed. All the area's chrome will also need to be removed, or the welded will need to wear a elaborate respirator to do the job.
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#13
I can not tell from the photo if its one piece or a threaded center stud. The original poster is MIA.

But if the process is as involved as you suggest its not economically practical.

What would be more practical is to cut and drill the post out than tap the hole for a screw in stud.

Either way its a PITA.
Never Give Up!!!
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#14
Hi all. I am back from MIA status. The maidens at Castle Anthrax granted me special leave. I appreciate all the help. If the stud had been threaded in place, I think it would have come out. I really leaned on the screw extractor aka easy-out. So much so, that I feared something would break if I went any harder. I have a donor frame from which I could harvest a pivot axle. What is the proper nomenclature for the broken part anyway? OR, maybe I could tap the base piece, to accept the threaded replacement stud (http://problemsolversbike.com/products/cantilever_stud/). But the damn replacement stud is probably metric-threaded.
The reason I was MIA, is that I had the bike, but then returned it. But now I have it back again, permanently. If I make progress, I will try to remember to make note of it here. Thanks again. Chris.
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#15
UPDATE: Heard from someone at HARO:

"I believe that the brake post on those frames were
welded on to the frame.
Kellen LeBlanc
Product Service Manager | Haro Bikes"
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#16
Okay, problem solved. From local bike shop, got a replacement pivot stud (they called it a brake boss). There were several different male thread choices. I found one that had male threads the same size as the female threaded end, which accepts the bolt that holds on the brake arm. The broken bit on the frame has those same female threads, except now they are messed-up because I ran a screw extractor in, thinking I would get the broken stud aka boss out. Only to find the stud is not threaded on my HARO frame. So anyway, hopefully the shop will also have the metric tap so I can clean-up the threads. Happy happy.
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