Brompton 2 speed shifting issue

doginabag

Senior Member
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. :laugh:

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?
 
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. :laugh:

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

steveindenmark

Legendary Member
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.
 

Kell

Über Member
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.
 

mitchibob

Über Member
Location
London, UK
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.
 

Tenkaykev

Veteran
Location
Poole
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.
 
OP
OP
doginabag

doginabag

Senior Member
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.

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.

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

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.

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.
 

Kell

Über Member
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
 

Schwinnsta

Well-Known Member
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.
 
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,


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. :laugh:

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?
 

Kell

Über Member
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.
 

Tenkaykev

Veteran
Location
Poole
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.
 

shingwell

Well-Known Member
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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