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ratdog 04-03-13 07:33 AM

cracked Brompton rear triangle
I was cleaning up the Bike to get it ready for Spring and noticed a 1/4" (3mm) crack on the tube that extends out for the left roller wheel. Was kind of bummed out about it, but have read lots of comments that this will not affect the structural integrity of the rear triangle, but will only make the bike hard to roll on 3 wheels if the crack ever travels enough to have the wheel fall off.

I did notice that the roller was slightly bent last year, but didn't think it was cracked because the damage was hidden by the hook of the shock cord that came with the rack.

I got me thinking,... has anyone ever changed out a Brompton rear triangle? If so, did you do it yourself or have the local dealer do it? I think I'm going to wait until the skate wheel is unuseable, but just wanted to know for the future.

rhenning 04-03-13 07:52 AM

If you bought the bike new and didn't crash it I would be contacting Brompton for a replacement frame. I wouldn't be thinking about fixing it myself. If it is a used bike find a frame builder and ask him or her what to do. Roger

ratdog 04-03-13 08:30 AM

Not new, the bike is about 7 years old, bought as new from Channell Wasson and was never in a crash. Damage looks like it was caused by either impact to or too much weight on the skate wheels when the bike is in a folded position. Thing is, I baby my bicycles and don't ever remember doing anything that may have caused this.

I guess I could have someone look at repairing this, but finding someone to do metal repair work in Manhattan is going to be tough.

Elvis Shumaker 04-03-13 08:52 AM

No useful suggestions, other than re. finding metal repair - any auto shop should be able to weld a bit of steel.

fietsbob 04-03-13 09:18 AM

Repeated hard set down in the rear fold.. , has that J bend continuing to bend more..

The solution I used was a steel strip, sharply bent, Hot forged, just at the original J to J end width, after bending them back up, [will be distortion from the prior metal stretching..being forced back.]

with a hole in each end for the roller 6mm bolt.. 'Easy wheel' is flat on the inside..
standard wheel got modified with a file, to be so.
then the strip across the top will not stretch more, better steel the better
Like 1/8" thick hotrolled, 3/4 wide flat bar ..

A repair brace from a commercial source, made in NL ..
you saw off the bent/cracked ones, and paint the 'wound'

if you can bend the J tubes back this is another brace..

BassNotBass 04-03-13 11:12 AM

No need to weld the crack... brazing is the best bet.

ratdog 04-03-13 12:43 PM


I love the way the repair braces look. Do you know how much work is involved in putting one on? It looks like you need to do some grinding and cutting to make this fit.

bhkyte 04-03-13 01:11 PM

I broken off the wheel mount on my old Merc. This was from afair standing on them to pull upp the stiff seatpost. Then I relasied that brompton manual states use the toptube.
Ori do some to attach to mezzo rack that might be apadtes, but proberly better to just get repaiired.

fietsbob 04-03-13 01:18 PM

I have yet to see one of the NL made ones first hand.. now forewarned , I just now inquired about
the second one I linked to as a belt and braces prophylactic addition, to a un damaged new bike..

using Chrome browser the language translate detection kicks in you just allow the translate.

My patch was done by a friend locally, as I described , the J tubes were able to be bent back,
rumpled a bit, ... then the fabricated piece slipped over, and the bolts screwed back in.

the NL repair bridge mentioned first , is anticipating an amputation of the J end, hacksaw and filed smooth,
and touch up paint, on the cut end.
It includes a replacement of the threaded boss for the Wheel axle bolt.

smallwheeler 04-04-13 11:04 PM

1 Attachment(s)

Originally Posted by ratdog (Post 15463741)
...finding someone to do metal repair work in Manhattan is going to be tough...

Elvis Shumaker 04-04-13 11:51 PM


Originally Posted by BassNotBass (Post 15464553)
No need to weld the crack... brazing is the best bet.

Even better. Any reputable restaurant in Manhattan should be able to do this.

kamtsa 04-05-13 09:13 AM

Another option is to get a replacement (different colors available).

BassNotBass 04-05-13 10:18 AM


Originally Posted by Elvis Shumaker (Post 15472277)
Even better. Any reputable restaurant in Manhattan should be able to do this.

I think that the bad restaurants would actually be a better bet. They're more adept at taking a culinary art like braising and reducing it to an act in which food becomes tenaciously bonded to the cookware.

ratdog 04-05-13 12:03 PM

FTR, BassNotBass is correct in that this needs to be brazed and not welded or "braised" like you would a duck. If I remember correctly, the two different processes bond metal to metal using different temperatures and if you attempt to apply a weld to the tube as a repair, you'll most like blow a hole right through the wall of the tube because of the higher temperature.

I imagine this repair if this is the eventual route I take, should be done by someone with craftsman type skills and not the guy down the block used to welding stainless steel restaurant sinks, ductwork or iron gates but would also need to be cost effective since the replacement cost is probably going to be about $180 if I do the installation myself.

ratdog 04-05-13 12:07 PM


Originally Posted by smallwheeler (Post 15472224)

Well, in the grand scheme of things, I guess I am, having only been here in NYC for a little over 50 years and on this forum for 8 years, so what's your point?

smallwheeler 04-05-13 06:40 PM

well then, i guess you have no excuse.

here's a secret: a dozen or so metal fabricators in chinatown below delancey around allen st. i've had several little projects done there over the past five years. always reasonably priced and reasonably competent. and yes, you can get bronze/ brass brazing down there too. probably get that little crack brazed while you wait.. or walk over to vanessa's dumplings..

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