Brompton rear hinge

[Bromptonlad]

looking at replacing the rear triangle, as it is all rusty… bushes are fine, no play, so I was thinking a straightforward swap. Any thought on these replicas fron China? I can’t afford a shop replacement
https://www.aliexpress.com/item/1005005182570031.html?src=google&src=google&albch=shopping&acnt=548-301-0399&slnk=&plac=&mtctp=&albbt=Google_7_shopping&gclsrc=aw.ds&albagn=888888&ds_e_adid=&ds_e_matchtype=&ds_e_device=c&ds_e_network=x&ds_e_product_group_id=&ds_e_product_id=en1005005182570031&ds_e_product_merchant_id=670068893&ds_e_product_country=GB&ds_e_product_language=en&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=20331137754&albag=&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gclid=CjwKCAiAibeuBhAAEiwAiXBoJAdSXfM6UGpb0Ydh41wnoyskrxdtArV0qORWoW3_JF9cjZMLV4HXwRoCtJAQAvD_BwE&aff_fcid=6133ea4abeb74c7e8e879e27157cac7c-1708018389211-03697-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=6133ea4abeb74c7e8e879e27157cac7c-1708018389211-03697-UneMJZVf&terminal_id=4ef24ec12a9544c5810a3ad130fd554c&afSmartRedirect=y

[rogerzilla]

It's probably from a 3Sixty or similar clone.  The Brompton ones are no great shakes so I wouldn't worry too much about strength; whether it will actually fit properly is the question.

If you're going to the trouble of removing the twin bolts of hell, you will want to change the bushes.

[Bromptonlad]

I looked at a video, it seems all I have to do is to undo a 5 mm Allen key, there should be no need to remove the bushes, use taps and all that stuff…
The rear frame is Aceoffix

[LittleWheelsandBig]

Good luck.

[rogerzilla]

I looked at a video, it seems all I have to do is to undo a 5 mm Allen key, there should be no need to remove the bushes, use taps and all that stuff…
The rear frame is Aceoffix

How-to videos are not to be trusted.  You need a 5/32" allen key.  Do not attempt to use a metric one (4mm seems right but isn't), as it will not fully engage and you may round the hex.  The bolts are normally impossibly tight and I have always had to drill the heads off them.  Once you've spent two hours getting it apart, it is very much worth having a Brompton dealer fit and ream new bushes.

[drossall]

Well, some years after doing that friend's bike (see up-thread), it looks like it's time to do mine. Although I borrowed LWaB's reamer last time, I've since managed to obtain one. Wish me luck

I did manage to replace the seat post sleeve, which was another reaming job. That's worked really well

[Bromptonlad]

Right, so not as simple... I suspect it is down to the heavy duty threadlock they use.
The toolset required to replace the bushes, as far as I can see is not worth investing in for a job that I will likely never do again. Equally, paying a shop to do the all job, including paying for an original rear frame is likely to cost several hundreds... so again, not worth it...
Alternative could be having a total respray/coat, but I would need to separate the rear triangle, so the same problem exists.

Sounds like the best course of action is to let it rot until it fails and at that point sell it on Ebay for parts or take it to the local recycling centre. It might well last another 5 years problem free. Could be double that, if I didn't use it in winter... but then I would be looking at 15-20 quid per week in bus fares... 250 pounds in public transport per winter, give or take.

[drossall]

Where are you and is the issue removing the bushes, or the reaming, or both?

For the removal, see comments above on the size of Allen key and the hacksaw trick, which is what I'm planning to use for my second replacement job (but carefully!)

[rogerzilla]

The only real special tool is the reamer.  My local Brompton dealer charges a minimal amount to fit and ream new bushes if you do the grim job of removing all the old stuff.  The old bushes generally come out with a 7/16" tap (yes, more imperial tools*) and a drift from the other side.

*an M10 tap works most of the time but can just rip out.  They are glacier bushes; an unholy laminate of bronze, steel and dimpled plastic, which is the actual bearing surface.  An M10 tap only grips the soft plastic.

[drossall]

Hmm. The screws actually both came out with an Allen key, albeit using a ratchet handle and not the toy that comes with the Brompton kit. But the bushes are stuck fast. The tap holds fine in the bush, but nothing moves when I hit the drift (I'm using the old spindle). I've seen advice elsewhere to consider cutting through them (carefully!) with a hacksaw blade, and then working round them knocking them free. Anyone tried GT85 or similar successfully?

[rogerzilla]

I tried all sorts before I cut them out.  There is some kind of dissimilar metal corrosion going on.

[drossall]

Thanks - saved me a lot of time looking for other methods, anyway! I'll give it a go at the weekend, when I can spend a little time. Obviously it was your post that I saw in the thread elsewhere.

[rogerzilla]

It is not terribly easy.  A razor file might be a better tool than a junior hacksaw blade.  When you have made a slot (or two), carefully tap it inwards with something pointy and a mallet. It will let go eventually.

[drossall]

I've ordered a handle for the blade (because, obviously, a normal junior hacksaw frame isn't going to work). Hoping that helps, but will consider a file if not.

I did wonder whether it's possible to drive the tap in too far, to the point that it engages in the tube beyond the bush, but I don't think that's the issue.

[Jurek]

I've never done this job so, by all means, confine me to the 'doesn't know what he's talking about' bin, but a jeweller's piercing saw, with a deep throat, could be the easiest solution here.
Were it me, I'd probably make two cuts, as close to 180° opposite each other as poss, then give it some hammer and drift.

[drossall]

And I've never seen a jeweller's piercing saw

The ones I've just Googled are hacksaw-like. The problem with that is that we're discussing cutting a small, circular bush that has been inserted into the end of a tube. So a "framed" saw isn't going to fit. I don't think feeding the blade through, putting the saw back together, and doing both bushes at once would work, because I believe it would foul the central part of the tube, which is not reamed as are the ends. But any suggestion that makes it easier is really welcome, and I'll happily report back!

Here's Shane Cycles discussing the issue, and one of their photos showing the problem area:

[rogerzilla]

Ugh..USian grammar, "fit" rather than "fitted"

A custom drift only works when one bush is already out.

It's a crap design that lasts longer than it should based on the tiny bearing area, but at the cost of maintanability.  It's easier to change the hinge on a Moulton TSR, although they don't last long.

[Kim]

And I've never seen a jeweller's piercing saw

As an aside, after discovering parallel action pliers, I can thoroughly recommend an hour spent down the learning-about-jewellers'-tools rabbit hole.  Some of them are surprisingly useful.

[drossall]

New bush for comparison. Wasn't too bad actually. To get enough pressure on the hacksaw, I had to feed the blade along the tube and then reassemble it onto its handle. Then I sawed both bushes at once. I got through the thickness easily, as you'd expect, but then had to chisel the bits out with a screwdriver and the butt of my hand. One fell out when I wasn't looking, which confused me, in spite of being corroded in solid when I started. It seemed as though each bush had one patch of corrosion somewhere, and would shift once that was freed.

I put a thin film of copper grease on the outside of the new bushes. Hope that helps next time!

[rogerzilla]

Mine looked even uglier than that by the time they came out!

[drossall]

Hmmm. Now I've got a constant rattle. Any ideas? Probably better in that linked thread, unless you think it's the new hinges (I don't).

[rogerzilla]

Rattle is usually the rear hub.  Squeak is usually the suspension block bolt.

[drossall]

What rattles in the hub? Not the 3-speed presumably, so the sprockets and Brompton-specific parts? It does sound rather like a badly-running chain except that, as I said, it happens when I'm not pedalling just as much as when I am.

Should the suspension bolt contact the seat bolt? Presumably not?

[rogerzilla]

Yes, the 3-speeds rattle, especially the BSR/SRF3 with its pawl actuator plate.

If it's chain rattle, check the chainline with a straight edge.  The new hinge may have displaced the rear triangle slightly to one side.  You can move spacer washers about to get the jockey wheels and sprocket in line.

[drossall]

Not chain rattle I think because, as I said, it happens whether or not I'm pedalling.

I'll have to take another look at the weekend. Thanks for the advice. Would still appreciate comment on whether those two bolts should make contact, and/or photos of how they look on other people's bikes.