# Brompton 2 speed shifting issue



## doginabag (18 Jul 2019)

I have just given my 6 speed it's first proper service, after three years and ~8000 miles the rear tyre was down to canvas and the amount of gunk on the drive train needed chiselling off. 

It's all cleaned up good, the change to kojaks has made it feel like a whole different bike, brakes are nice and sharp again, but the gearing is not great. The hub is fine, but the shifter when in low keeps jumping, when in high it is fine.

I thought it would be s tension issue, but moved to the lowest tension setting the issue remains. 
I did replace the chain, mainly because I lost one half of the quick link, but it was pretty worn. However the sprockets are still the originals, could a new chain on worn sprockets be the issue?

I have already ordered some replacements anyway, but could there be something else I hadn't thought of?


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## raleighnut (18 Jul 2019)

doginabag said:


> I have just given my 6 speed it's first proper service, after three years and ~8000 miles the rear tyre was down to canvas and the amount of gunk on the drive train needed chiselling off.
> 
> It's all cleaned up good, the change to kojaks has made it feel like a whole different bike, brakes are nice and sharp again, but the gearing is not great. The hub is fine, but the shifter when in low keeps jumping, when in high it is fine.
> 
> ...


I'd put money on it being a worn sprocket.


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## Schwinnsta (19 Jul 2019)

Up the tension on the shifter.


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## steveindenmark (19 Jul 2019)

I am amazed you have been able to pedal for so long. I have had my Brompton for less than a year and took the chain tensioner off to soak last week.

Clogged with the solidified bodies of dead slugs 

Did you sort the gear problem.?

Tighten the 2 tiny screws in the centre of the gear lever housings and see if that helps.


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## Kell (19 Jul 2019)

doginabag said:


> I did replace the chain, mainly because I lost one half of the quick link, but it was pretty worn. However the sprockets are still the originals, could a new chain on worn sprockets be the issue?


 
This will be the cause.

After that amount of time the chain ‘stretches’ (well, it doesn’t, the rollers wear and the links get a little further apart). Because these are further apart, they wear the sprockets in a different way.

So that when you put the new chain on, it doesn’t sit on them properly - especially under load.

If you change your chain before it wears, you can get away with not changing the sprockets (apparently), but i’ve never successfully managed it.

I swap mine out twice a year (chain, sprockets and chainring) as a matter of course. Once before the winter and once just after.


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## mitchibob (19 Jul 2019)

You should pretty much always replace the sprockets at the same time as the chain. Cheap and easy to do. Chainring a little less often perhaps.


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## Tenkaykev (19 Jul 2019)

I've fitted a few bits to my wife's Brommie and my own ( Brompton rack, new chainwheel, and a Brompton dynamo wheel kit etc), and looked at some of the official Brompton maintenance videos on their Web page. 

I've noticed that the instructions that come with the various replacement parts are a bit hit and miss and could be clearer.
A pity there isn't a " Haynes Manual" with clear diagrams / photos and step by step instructions.


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## doginabag (19 Jul 2019)

raleighnut said:


> I'd put money on it being a worn sprocket.


I expect/hope so to, I was just trying to pre-empt any other possible causes just in case.



Schwinnsta said:


> Up the tension on the shifter.


If anything it needs the tension reduced which I tried with no effect. I have actually increased the tension for now just so keep it on the functioning sprocket.



steveindenmark said:


> I am amazed you have been able to pedal for so long. I have had my Brompton for less than a year and took the chain tensioner off to soak last week.
> 
> Clogged with the solidified bodies of dead slugs
> 
> ...


Some of it did need to be chiselled out of the tensioner wheels with a jewellers screwdriver but it feel much nippier now!



Kell said:


> This will be the cause.
> 
> After that amount of time the chain ‘stretches’ (well, it doesn’t, the rollers wear and the links get a little further apart). Because these are further apart, they wear the sprockets in a different way.
> 
> ...





mitchibob said:


> You should pretty much always replace the sprockets at the same time as the chain. Cheap and easy to do. Chainring a little less often perhaps.


Thanks both. I have the new sprockets here now so will get them changed over tonight. 
I only planned to change the tyres over and put on a new set of brake pads, but as I started looking closer and saw how much grime was it escalated into a full service which I wasn't expecting to do. I knew the chain was worn but was going to give it a clean and put it back and replace it with the sprockets later, but I carelessly lost one half of the quick link. I got a replacement chain from my local bike shop, but they don't deal with Bromptons so couldn't get the sprockets at the same time.


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## Kell (19 Jul 2019)

I also clean out the jockey wheels about once a month. 

They get unbelievably clogged up. Use a screw driver to push through the gaps as shown. 


View: https://youtu.be/E4nh0aEiBeI


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## Schwinnsta (19 Jul 2019)

When there is no tension on the shifter cable, the chain goes to the smallest gear (low). So if it is coming off of the larger cog, it is likely that the tension is too low and it is self shifting.


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## raleighnut (19 Jul 2019)

Schwinnsta said:


> When there is no tension on the shifter cable, the chain goes to the smallest gear (low). So if it is coming off of the larger cog, it is likely that the tension is too low and it is self shifting.


It's not working on the large cog though,




doginabag said:


> I have just given my 6 speed it's first proper service, after three years and ~8000 miles the rear tyre was down to canvas and the amount of gunk on the drive train needed chiselling off.
> 
> It's all cleaned up good, the change to kojaks has made it feel like a whole different bike, brakes are nice and sharp again, but the gearing is not great. The hub is fine, but the shifter when in low keeps jumping, *when in high it is fine*.
> 
> ...


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## Kell (19 Jul 2019)

mitchibob said:


> You should pretty much always replace the sprockets at the same time as the chain. Cheap and easy to do. Chainring a little less often perhaps.



Yeah, I never used to on my old bikes, and I've also heard that rotating the chainring forward on the spider helps (as it put the teeth under load in a different place) but I'm not sure it's do-able on a Brompton because of the way it attaches.

For the sake of 2x £25 a year, I just do it.


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## doginabag (22 Jul 2019)

New sprockets on and it is back to riding just as well as the day it was born.


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## Tenkaykev (22 Jul 2019)

I had one of those " oh, that's clever" moments when I was giving my second hand Brompton it's first clean. 
At first I thought the small sprocket on the derailleur was damaged, closer inspection revealed that some of the teeth are skewed to compensate for the thinness of the sprocket and better fit into the chain.


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## shingwell (22 Jul 2019)

Yes since I bought my second hand B I have had numerous "oh, that's clever" moments! The latest was noticing how the front mud flap, when the bike is folded, covers the oily chainring to help you stay clean.


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## Fields Electric (29 Mar 2021)

Just sorted out an issue on mine, it refused to shift to the smaller sprocket. But twisting the shifter outward by hand would get it to shift. I put a bit more slack in the cable, which solved the issue. It was only a problem with a worn chain. But it’s been there since new, some 5000 miles ago. I am currently trying to get 1200 miles out of a chain. Sprockets and chain ring are definitely past there best.


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## rogerzilla (20 Jun 2021)

The wearable parts of the derailleur mechanism aren't particularly expensive, just a bit fiddly to fit (the cable is particular fun, especially if you use a generic SA trigger cable as the inner wire). The external spring tends to rust, so it's worth an occasional replacement.


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## berlinonaut (22 Jun 2021)

rogerzilla said:


> The wearable parts of the derailleur mechanism aren't particularly expensive, just a bit fiddly to fit (the cable is particular fun, especially if you use a generic SA trigger cable as the inner wire). The external spring tends to rust, so it's worth an occasional replacement.


Worth mentioning that, once more, you seem to refer to an outdated design. Brompton changed the design of the shifter already back in 2017 and along with that came a new dogleg which makes changing the derailleur cable way easier than with the old design.


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## rogerzilla (22 Jun 2021)

True, but there are probably as many pre-2017 Bromptons about as post-2017. They still sell the old type of dogleg mechanism, too - I've just fitted a new one to a 2005 S6L.


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