Gear changing on 6 speed Brompton

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Philip Benstead
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Gear changing on 6 speed Brompton

Postby Philip Benstead » 11 Jan 2021, 4:24pm

Gear changing on 6 speed Brompton.

I have a 6 speed Brompton post-2018.

I cleaned the Brompton over the Christmas period taking out the wheels and washing thoroughly.

I release the wheels I found the following:
I am having trouble with the rear derailleur.

When I change to the small cog to the large cog the chain moves cleanly
When I change from the large cog to the small cog the piolet mechanism moves but the chain will not move.

The only thing I can think is that the rear derailleur arm is worn, and that the piolet mechanism is able to push the chain over enough?

ANY IDEAL WHAT IT COULD BE

NB
I have tried adjusting the limit screws to enable the pivot mechanism to move the jockey wheel as far as possible.
The bike is clean including drive train.
The chain is not worn.

Once I found I was having trouble with the gear I inspected the following:
The pivot gear changer is free moving and there is a washer under the mechanism as required.
The jockey wheels on the derailleur are free moving.
The spring is free moving.
The gear cable is free moving.
The gear lever is free moving.
All parts have been clean with a degreaser.
All parts have been lubricated with either semifluid Silicon or Silicon grease.
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

Brucey
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Re: Gear changing on 6 speed Brompton

Postby Brucey » 11 Jan 2021, 5:13pm

If the limit screws are set correctly, and you have reassembled correctly, the usual cause of this is that the springs are not springing enough or the cable is draggy. Third possibility is that the guide pulley is worn.

Needless to say there is no point in cleaning worn parts; they belong in the bin. And cables on Bromptons should just be replaced if there is the slightest doubt about them; they don't last for ever, not with the folding.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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Philip Benstead
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Re: Gear changing on 6 speed Brompton

Postby Philip Benstead » 11 Jan 2021, 5:48pm

Brucey wrote:If the limit screws are set correctly, and you have reassembled correctly, the usual cause of this is that the springs are not springing enough or the cable is draggy. Third possibility is that the guide pulley is worn.

Needless to say there is no point in cleaning worn parts; they belong in the bin. And cables on Bromptons should just be replaced if there is the slightest doubt about them; they don't last for ever, not with the folding.

cheers


Many thanks

Yes, I thought it was the jockey wheels.
I found new ones here https://www.condorcycles.com/products/b ... eid=196673
I am surprised they wore so quickly. Like I said above the piolet is moving but not enough. The changing is smooth and is not dragging. The spring is clean and free moving.

What I do understand, that until I clean the Brompton everything was working fine.
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

rmurphy195
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Location: South Birmingham

Re: Gear changing on 6 speed Brompton

Postby rmurphy195 » 12 Jan 2021, 10:55am

What you don't say is how you are changing the rear derailler - is it static, or with the wheels and pedals rotating?

The Brompton 6, assuming its like mine, is a combination of a hub gear (which requires hub gear techniques to change) and a derailleur which requires derailleur techniques i.e. pedalling without a load, so the chain can move freely NOT undeer tension.
Brompton, Condor Heritage, creaky joints and thinning white (formerly grey) hair
""You know you're getting old when it's easier to ride a bike than to get on and off it" - quote from observant jogger !

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Philip Benstead
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Re: Gear changing on 6 speed Brompton

Postby Philip Benstead » 12 Jan 2021, 11:20am

rmurphy195 wrote:What you don't say is how you are changing the rear derailler - is it static, or with the wheels and pedals rotating?

The Brompton 6, assuming its like mine, is a combination of a hub gear (which requires hub gear techniques to change) and a derailleur which requires derailleur techniques i.e. pedalling without a load, so the chain can move freely NOT undeer tension.


I am pedalling whilst changing gear on the derailer.

Its been suggested that I should try flipping the jockey wheels over.
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

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Philip Benstead
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Re: Gear changing on 6 speed Brompton

Postby Philip Benstead » 13 Jan 2021, 5:30pm

Brucey wrote:If the limit screws are set correctly, and you have reassembled correctly, the usual cause of this is that the springs are not springing enough or the cable is draggy. Third possibility is that the guide pulley is worn.

Needless to say there is no point in cleaning worn parts; they belong in the bin. And cables on Bromptons should just be replaced if there is the slightest doubt about them; they don't last for ever, not with the folding.

cheers


I have replaced the
jockey wheels
the gear cable inner and outer

I have tried adjusting the cable tension and limit screw again
I have looked at the cable instruction but still won't change it looks like the spring.
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

drossall
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Location: North Hertfordshire

Re: Gear changing on 6 speed Brompton

Postby drossall » 13 Jan 2021, 6:58pm

Brompton transmissions do wear quickly, and do need to be kept clean more than usual. But, on my 2012 model, a new chain, sprockets and jockey wheels had it shifting like new.

Andy Short
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Location: Bristol

Re: Gear changing on 6 speed Brompton

Postby Andy Short » 13 Jan 2021, 8:01pm

I had something similar on mine after taking the wheel out. I can't recall exactly what it was, but it was something to do with the plastic part that goes between the frame and 'hollow' nut. It might have been a spacer misplaced or something and the plastic housing wasn't sitting correctly. It was obvious when I took the wheel nut off and checked everything was correctly placed.
The other possibility is the cable routing or lubrication?

Brucey
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Re: Gear changing on 6 speed Brompton

Postby Brucey » 13 Jan 2021, 8:17pm

Andy Short wrote:I had something similar on mine after taking the wheel out. I can't recall exactly what it was, but it was something to do with the plastic part that goes between the frame and 'hollow' nut. It might have been a spacer misplaced or something and the plastic housing wasn't sitting correctly. It was obvious when I took the wheel nut off and checked everything was correctly placed....


lockwasher part HMW526 sits between the frame and the derailleur bracket;

Image

this part is not symmetric, and if it is misplaced (eg inverted) the derailleur will sit at a strange angle and may indeed not shift correctly.

cheers
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Philip Benstead
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Re: Gear changing on 6 speed Brompton

Postby Philip Benstead » 15 Jan 2021, 5:37pm

Philip Benstead wrote:
Brucey wrote:If the limit screws are set correctly, and you have reassembled correctly, the usual cause of this is that the springs are not springing enough or the cable is draggy. Third possibility is that the guide pulley is worn.

Needless to say there is no point in cleaning worn parts; they belong in the bin. And cables on Bromptons should just be replaced if there is the slightest doubt about them; they don't last for ever, not with the folding.

cheers


I have replaced the jockey wheels (BTW they cant be fliped over)
the gear cable inner and outer

I have tried adjusting the cable tension and limit screw again
I have looked at the cable instruction but still won't change it looks like the spring.

It tried to change gear sometimes but was struggling
So, I have changed the spring assembly, it fiddley thing to do. It worked first time.

I inspected the spring that I removed. I could not find anything wrong with it???

I suggest that this spring assembly is too sensitive and should be resigned.

Any views
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

Brucey
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Re: Gear changing on 6 speed Brompton

Postby Brucey » 15 Jan 2021, 8:41pm

IIRC the springs have to be stronger than one another (inside vs outside) on the shift one way and strong enough to overcome friction (eg in the spring mechanism, the pusher itself and cables etc) in the other direction. IIRC the latter applies to the shift into the small sprocket. The whole setup is also sensitive to the exact cable length used too. Hence my earlier comment about changing the cables if there is any doubt about them.

The whole spring mechanism has been redesigned at least once and you should have the later version. I'm always amazed it usually carries on working, even when the outer spring is covered in mud and going rusty, but it does....

cheers
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Boring_Username
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Re: Gear changing on 6 speed Brompton

Postby Boring_Username » 15 Jan 2021, 9:43pm

Philip Benstead wrote:ANY IDEAL WHAT IT COULD BE


Are you from Bristol?

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Philip Benstead
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Re: Gear changing on 6 speed Brompton

Postby Philip Benstead » 15 Jan 2021, 10:12pm

Boring_Username wrote:
Philip Benstead wrote:ANY IDEAL WHAT IT COULD BE


Are you from Bristol?


No, Why?

See above it was the spring
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

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Philip Benstead
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Location: Victoria , London

Re: Gear changing on 6 speed Brompton

Postby Philip Benstead » 15 Jan 2021, 10:14pm

Brucey wrote:IIRC the springs have to be stronger than one another (inside vs outside) on the shift one way and strong enough to overcome friction (eg in the spring mechanism, the pusher itself and cables etc) in the other direction. IIRC the latter applies to the shift into the small sprocket. The whole setup is also sensitive to the exact cable length used too. Hence my earlier comment about changing the cables if there is any doubt about them.

The whole spring mechanism has been redesigned at least once and you should have the later version. I'm always amazed it usually carries on working, even when the outer spring is covered in mud and going rusty, but it does....

cheers


I concur, then what preventive measure could one take to minimize this problem occurring too often?
Philip Benstead | Life Member Former CTC Councillor/Trustee
Organizing events and representing cyclist in southeast since 1988
Bikeability Instructor/Mechanic

Brucey
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Re: Gear changing on 6 speed Brompton

Postby Brucey » 15 Jan 2021, 10:55pm

instinctively I think keeping the spring clean ought to help. Cables on Bromptons seem to die depending on how often they get flexed, so more folding = shorter cable life.

cheers
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