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Old 07-06-17, 05:07 AM   #1
Paulash
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Fitting a new rear triangle to an elderly Brompton

Hello from sunny South Africa ....

I have an elderly Brompton on which I have been trying to install a BWR gear upgrade. The big snag, I discover too-too late, is that this ancient frame does not have the lug (the "HXB" in the Brompton manual) on which to attach the chain pusher assembly.

Since I cannot face the extreme hassle and expense of returning the parts (because I live in Johannesburg and the nearest Brompton dealer is 6000 miles away) I need to find a way of installing a lug.

The obvious solution would be to buy a rear frame off eBay. However, I understand I will need a special reaming tool to seat the bushes.

Is this, in fact, the case? How difficult is it to swap the rear triangle?

My other options are:

1. Make my own lug using the head(s) of correctly sized hex bolts, with the centre drilled out, mounted on the frame with a replacement long bolt through the chain pusher.

2. Work out some other way of moving the chain - by hand, probably - between the sprockets.

3. Refit the knackered old 3-speed wheel and hub, abandon any touring plans, and hang the shiny new BWR wheel in the garage as an expensive reminder that a hexagonal shaped lug is the difference between joy and sadness.

I would truly appreciate any advice.

Thanks in advance.

Paul
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Old 07-06-17, 09:18 AM   #2
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You could find a local frame builder to weld a lug on for you.
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Old 07-06-17, 09:47 AM   #3
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You could find a local frame builder to weld a lug on for you.
Yeah, considering this. The trick will be to get the hex shape exactly right and in the correct orientation -- looking at whatever pictures I can find online, it seems the wingplate rests at a slight angle.

It's difficult not having a single other Brompton in this entire country (that I know of) to take a look at. Or take to a welder and say: "Make me one like this" (points to lug ...)
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Old 07-06-17, 10:00 AM   #4
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Yeah, considering this. The trick will be to get the hex shape exactly right and in the correct orientation -- looking at whatever pictures I can find online, it seems the wingplate rests at a slight angle.

It's difficult not having a single other Brompton in this entire country (that I know of) to take a look at. Or take to a welder and say: "Make me one like this" (points to lug ...)
Ah. My Brompton is 500 miles away or I could take some pictures for you. I will be back up there next week. It is possible Brompton could sell you the lug and give you the specifications to take to the welder.

MTA: You probably already saw this, but it has a very good diagram of the part:
http://www.vlerickfietsen.be/brompto...rframe/AFR.pdf

Last edited by RunForTheHills; 07-06-17 at 10:06 AM.
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Old 07-06-17, 10:14 AM   #5
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Ah. My Brompton is 500 miles away or I could take some pictures for you. I will be back up there next week. It is possible Brompton could sell you the lug and give you the specifications to take to the welder.
Ah, thanks, man. Some close up, high-res pics would be very much appreciated.

Have tried Brompton support already. The lug is part of the frame build, ie. it's not a "part" in the catalog.

And if I buy a new rear frame on ebay (and there are plenty available, all with lugs), the hassle continues: Brompton have stopped supplying the rear spindle and bushing kits (although a few dealers still have them) as well as the reamer tool.

I can't even order a rear frame from them -- nor from a dealer -- because only authorised Brompton dealers may replace the frame.

I am beginning to wish I had stuck with my original plan to buy a Bike Friday Pocket Llama during my trip to LA last year.

As much as I love the Brommie and its ludicrously small folded size, these various engineering "quirks" and proprietary parts could become unpleasant challenges in the places where I plan to ride.

Ah, well, maybe I'll have to stick to 3-speed touring ...
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Old 07-06-17, 11:27 AM   #6
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Why not fit a rear derailleur to your Brompton instead of the old chain tensioner..and then you could change between the two rear sprockets..You can buy cheap rear derailleurs that bolt on to the rear axle ..or you could find a frame builder to weld on a proper gear hanger...Chain might come off when you fold it possibly if it cannot take up all the slack in the chain ..but at least you could change gear OK..
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Old 07-06-17, 12:02 PM   #7
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Another way?

it is fairly easy if you go with a regular crank to use two chain rings and use the greasy finger shift method. Couple that with the wide spread ratios of the BWR hub and you would a very wide range indeed. There have been quite a few posts about the no-dérailleur 2 chain ring set up.
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Old 07-06-17, 03:09 PM   #8
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I recently serviced the rear frame hinge, using a standard reamer. I'd been worried about performing this job for a long time, I kept delaying it due to the potential trouble caused by my lack of experience. It all worked out OK and the brompton reamer isn't really necessary, a modicum of caution and diligence will do. The problem for me was getting the hinge bolts out.. in fact I resorted to an unorthodox method of sawing through the spindle instead of drilling out the bolts as drilling was taking forever.
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Old 07-06-17, 03:52 PM   #9
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Why not fit a rear derailleur to your Brompton instead of the old chain tensioner..and then you could change between the two rear sprockets..You can buy cheap rear derailleurs that bolt on to the rear axle ..or you could find a frame builder to weld on a proper gear hanger...Chain might come off when you fold it possibly if it cannot take up all the slack in the chain ..but at least you could change gear OK..
OK, this idea I like! Could you give me more detail, especially about the kind of cheap derailleur I should look out for.
Thanks very much.
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Old 07-06-17, 03:57 PM   #10
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it is fairly easy if you go with a regular crank to use two chain rings and use the greasy finger shift method. Couple that with the wide spread ratios of the BWR hub and you would a very wide range indeed. There have been quite a few posts about the no-dérailleur 2 chain ring set up.
Yeah, I discussed this with Brompton support. Their comment was that on bumps or rough road surfaces, the guide wheels could move and initiate a little uncommanded shifting on their own. But, I'll dig out the old posts and try this too. But the cheap derailleur idea is also a good one.

Meanwhile any cash that might have gone to more upgrades and new rear frames etc will go into a "brand new Brommie fund".

Thank-you all for your advice so far. Good to meet you all too. I'll let you know how things pan out.

cheers and thanks

Paul
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Old 07-06-17, 05:29 PM   #11
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OK, this idea I like! Could you give me more detail, especially about the kind of cheap derailleur I should look out for.
Thanks very much.

Haven't tried it but this shimano Tourney looks good since it has a short cage which will give better ground clearance than a long cager.



Shimano Tourney RD-FT35 Rear Derailleur with Hanger from BikeBling.com
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Old 07-06-17, 06:14 PM   #12
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Here's the thing as I see it. The normal setup provides a 2 gear change. A regular dérailleur is made to shift at least 5 up to 10. Making one work would be a lot of work for little gain. You could also just have 2 sprockets on the hub and shift those manually and I could see how it would be easy to have the chain jump from the big to the little as the chain tensioner for 1 and 3 speeds does not move from side to side so there could be chain line issues. I ran a 38/54 chainring combo on my brompton for a while and it never jumped from one chainring to the other.
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Old 07-07-17, 12:30 AM   #13
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it is fairly easy if you go with a regular crank to use two chain rings and use the greasy finger shift method. Couple that with the wide spread ratios of the BWR hub and you would a very wide range indeed. There have been quite a few posts about the no-dérailleur 2 chain ring set up.
Hi,

I was having a "dof" moment on my previous reply to you. I presume the double chain ring setup would use the original chain tensioner with the fixed guide wheels and not the one that comes with the BWR kit with its sliding guide wheels?

Certainly something to investigate, thanks for the steer.

cheers

Paul

Last edited by Paulash; 07-10-17 at 07:39 AM.
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Old 07-07-17, 02:59 AM   #14
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My Brompton is older. I bought the 5 speed SA hub and like it a lot. if I want more gears I think I would go for two chain rings in front and greasy finger shifting.

Edit: There used to be a guy from SA that posted in this forum. His B is new. No idea where in SA he is from but you could try to find his posts and maybe you are lucky and he is in your area.

Edit II: http://www.bikeforums.net/folding-bi...lding-box.html

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Old 07-07-17, 07:35 AM   #15
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I use the older version of the 5 speed hub and it's great. Ideal, in fact.
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Old 07-07-17, 09:19 AM   #16
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Some people seemed to be confused with what posted..I suggested a rear derailleur because Paulash has bought a BWR hub but he cannot fit the Brompton derailleur because he does not have the required braze on..Rec suggests a Shimano tourney rear derailleur..good choice because it has a short cage so some decent ground clearance..You need a Shimano Tourney that bolts onto the rear axle just like the old chain tensioner does..not the type of derailleur that bolts on to a gear hangar..There is no reason why this should not work that I can think of..You will also need an old friction shifter to operate it..either one for an old front derailleur would do or rear derailleur..Front changer would be better because it will be on the left side of the handlebars..
You are more likely to find everything in a bike shop that sells seconhand bikes or low end cheap bikes..
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Old 07-10-17, 05:13 AM   #17
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Some people seemed to be confused with what posted..I suggested a rear derailleur because Paulash has bought a BWR hub but he cannot fit the Brompton derailleur because he does not have the required braze on.
As it turns out, I found some small (3.5mm bore) hex nuts in my workshop. The fit into the wingplate is perfect. So am considering using two of these nuts and a long 3.5mm bolt to make my own HXB.

Can any of you perhaps tell me the distance in mm from the end of the frame tube to the centre of the HXB boss?

Also, I see from the diagrams that the HXB is a little off-centre -- is that correct? If so, a measurement across the tube to the centre of the HXB would also be extremely useful.

I would drill a 3.5mm hole right through the tube for the long bolt and secure it to the opposite side of the tube with an appropriate nut, washer and Loctite. 3.5mm is a small hole but could it weaken the frame in any way?

Quote:
Originally Posted by tudorowen1 View Post

Rec suggests a Shimano tourney rear derailleur..good choice because it has a short cage so some decent ground clearance..You need a Shimano Tourney that bolts onto the rear axle just like the old chain tensioner does..not the type of derailleur that bolts on to a gear hangar..There is no reason why this should not work that I can think of..You will also need an old friction shifter to operate it..either one for an old front derailleur would do or rear derailleur..Front changer would be better because it will be on the left side of the handlebars..
You are more likely to find everything in a bike shop that sells seconhand bikes or low end cheap bikes..
This is my back-up plan if the homemade HXB doesn't work out.

Thanks again to you all for your help. I'll keep you posted.

UPDATE: Brompton's Zendesk recommends against drilling into the tube. So, a Shimano derailleur is the next move.

Last edited by Paulash; 07-10-17 at 09:31 AM.
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Old 07-10-17, 01:01 PM   #18
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I would drill a 3.5mm hole right through the tube for the long bolt and secure it to the opposite side of the tube with an appropriate nut, washer and Loctite. 3.5mm is a small hole but could it weaken the frame in any way?



This is my back-up plan if the homemade HXB doesn't work out.

Thanks again to you all for your help. I'll keep you posted.

UPDATE: Brompton's Zendesk recommends against drilling into the tube. So, a Shimano derailleur is the next move.
This is not something I would do. Makes me cringe just reading about it.

my B is older just like yours so I am sorry I can not help you with the info you need.
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Old 07-11-17, 08:23 AM   #19
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This is not something I would do. Makes me cringe just reading about it.

my B is older just like yours so I am sorry I can not help you with the info you need.
No worries, man. After sleeping on it, have decided to try the Shimano derailleur idea and if that doesn't work then I will buy a new, complete frame next time I'm in the UK.

Meanwhile, I'll live with a slightly odd three-speed with a *very* wide gear range.

cheers

Paul
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Old 07-11-17, 09:12 AM   #20
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No worries, man.

cheers

Paul
I am not a man.

Cheers

bm
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Old 07-11-17, 09:16 AM   #21
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I am not a man.

Cheers

bm
I apologise

Are you really a bad mother, though?
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Old 07-11-17, 12:33 PM   #22
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I apologise

Are you really a bad mother, though?
Yes, that is why I picked that name
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Old 07-12-17, 11:09 AM   #23
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Just a few more thoughts on your dilemma..If you find a cheap dearailleur that bolts onto the axle you may have to modify the part that bolts onto the axle with a file..or perhaps get it welded on..
Possibly find a normal derailleur that bolts on and make a bracket that would attach slightly in front of the rear axle where the Brompton derailleur is situated on more modern bikes..That bracket could easily be welded on or held on with a jubilee clip or two..
Dahon fitted rear derailleurs in front of the rear axle for quite a time..If you do get one to work it may not be necessary to fit a chain tensioner but if you do it will have to be one made for the 2 or 6 speed Brompton ..the standard chain tensioner for the 3 speed hub would not work..I am sure if you can find a bike frame builder or competent welder/engineer/mechanic you should be able to sort it out ..
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