Dogleg

[Kell]

Slightly convoluted story...

I recently had to replace a rim, so got the hub serviced and new sprockets on the back.

The new ones seem to come with a yellow plastic spacer rather than the old metal one, and I was having some difficulty shifting down on to the lower cog. i.e. when changing down from 5th to 4th. I could shift the hub gears, but not the sprockets.

I know I'm still on my original chain tensioner, and it's looking like it's out of alignment and fairly worn, so bought a new one and fitted that, but it only seemed to make things worse.

I ended up tinkering with the spacer, and re-installing my original tensioner and everything shifts as it should.

As far as I can tell, the reason it wouldn't shift is that the spring in the dogleg didn't seem to have enough power/tension in it to push the new jockey wheels far enough over to shift. Remove the chain tensioner and it would do it, and it would eventually do it on my old worn one with a bit of fettling as it's so loose it doesn't offer up much resistance.

For the record, the grub screws are not preventing it from making the shift - everything is as it was before the sprockets were replaced.

So, my question is this. Is there a way to increase the power in that spring without replacing it? I don't want to just buy another one if there's something obvious I could do.

Or would replacing it give it the extra punch it needs to make the shift?

 

[Tenkaykev]

Slightly convoluted story...

I recently had to replace a rim, so got the hub serviced and new sprockets on the back.

The new ones seem to come with a yellow plastic spacer rather than the old metal one, and I was having some difficulty shifting down on to the lower cog. i.e. when changing down from 5th to 4th. I could shift the hub gears, but not the sprockets.

I know I'm still on my original chain tensioner, and it's looking like it's out of alignment and fairly worn, so bought a new one and fitted that, but it only seemed to make things worse.

I ended up tinkering with the spacer, and re-installing my original tensioner and everything sifts as it should.

As far as I can tell, the reason it wouldn't sift is that the spring in the dogleg didn't seem to have enough power/tension in it to push the new jockey wheels far enough over to shift. Remove the chain tensioner and it would do it, and it would eventually do it on my old worn one with a bit of fettling as it's so loose it doesn't offer up much resistance.

For the record, the grub screws are not preventing it from making the shift - everything is as it was before the sprockets were replaced.

So, my question is this. Is there a way to increase the power in that spring without replacing it? I don't want to just buy another one if there's something obvious I could do.

Would replacing it give it the extra punch it needs to make the shift?

Obvious question, is the new spacer the same thickness ?

 

[berlinonaut]

What year is the bike, so older or newer version of the dogleg?

 

[Kell]

Obvious question, is the new spacer the same thickness ?

it looks thicker to me. I ended up hacksawing it in half. I didn't fit the sprockets. They were already on when I picked up the wheel. I didn't want them fitted as they charged me to do it, but ended up refunding the money as I'd never said I wanted them fitted. Takes less than two minutes to remove and replace and they charged £20.

This is the kit that was fitted versus the one I did have fitted (below). When comparing data, it did say the spacer should be 2.5 mm. The yellow plastic one looked to be thicker than that. So I thinned it down (the fettling I was talking about).

What year is the bike, so older or newer version of the dogleg?

2015.

 

[Kell]

Is it possible the cable is sticking in the housing? They're the originals.

 

[u_i]

You did play with limit screws. Right? You washed the area just in case. Correct? There are many things that can go off there.

In any case, as to the limited-scope question of increasing the force of the return spring, what I did is to increase the net length of the spring. Specifically, I cut off a short piece of a replacement spring and fitted it that piece next to the regular spring on the pusher tube. (There is a limit on the amount of the extra length that you can fit.) I separated the two with a washer on the tube, so they could not mangle together. Of course, with the increased return force of the spring, it got tougher to mount the pusher.

In the aftermarket, you can find replacement springs that are supposed to be stiffer than the original, but their diameter is too large and they are more prone to deform permanently than the original spring.

 

[berlinonaut]

When comparing data, it did say the spacer should be 2.5 mm. The yellow plastic one looked to be thicker than that. So I thinned it down (the fettling I was talking about).

Our of curiostiy: why didn't you simply use the old one?

2015.

This means we are talking about the old dog leg and the old shifters. So it is probably not the cable (which is somewhat common with the new version) and also the dogleg mechanism could not disconnect itself from the frame. The two speed is pretty robust, but if you have an issue with it it can be pretty annoying.
You could rise the tension of the cable inside the shifter (there are two or three tension steps once you open it) but I doubt that this is your problem. I would clean the whole system around the shifting fork on the frame, make sure it's screw is not too tight (and neither too loose) and possibly replace the fork thingy. It is intended as a consumable after many miles and depending how many miles you did on the bike and in which conditions it may be the case that tolerances have added up and with the new sprockets it ended up to be just too much.
But this is just a bet, not a safe statement.

 

[Schwinnsta]

If the plastic part attached to the top of the metal part of the chain pusher is not clean, the shift can not happen. This piece can and does trap dirt as it has both a horizontal shelves and vertical walls. The dirt can prevent the shift by not allowing the adjustment screws to fully travel to vertical walls of this plastic top part of the chain pusher. This has certainly happened to me.

 

[u_i]

If the plastic part attached to the top of the metal part of the chain pusher is not clean, the shift can not happen. This piece can and does trap dirt as it has both a horizontal shelves and vertical walls.

Also, as @berlinonaut pointed out, if the screw connecting the pusher with the dogleg is overtightened, then the pusher will not shift properly.

 

[Kell]

Our of curiostiy: why didn't you simply use the old one?

Because I didn't fit them.

As mentioned above, I asked if they had any in stock when I put my wheel in for a rebuild, when I picked it up, they were already fitted. Which is odd, they had no idea that I didn't want them for a different bike.

I did check to ensure that they were correct for the bike as I'd not seen them before, but my usual sites for parts (SJS and Brilliant Bikes) are now selling this version. But, as I didn't think there would be any problems I didn't ask for the old spacer.

As said, everything works perfectly with my old chain tensioner (used my bike this morning with absolutely no issue) , but I wanted to replace that as the jockey wheels are so worn they no longer operate on a vertical plane, so the chain doesn't run in a straight line.

It just feels like the spring isn't powerful enough to push against the resistance of the top jockey wheel on the new chain tensioner. The dogleg is not massively expensive, so I might just get a new one and see if that works.

 

[berlinonaut]

The dogleg is not massively expensive, so I might just get a new one and see if that works.

Unfortunately the older version that you need seems to be more expensive than the newer version:
new: https://www.sjscycles.co.uk/gear-sp...ing-set-complete-for-integrated-gear-shifter/
old: https://www.sjscycles.co.uk/gear-spares/brompton-dr-spring-set-cable-stop-for-gear-trigger-pre2017/

If you order anyway think about if the chain pusher would be worth it as well:
https://www.sjscycles.co.uk/gear-spares/brompton-dr-chain-pusher-assembly/

 

[Kell]

I'd already ordered the dogleg, so will leave the chain pusher for now.

It appears to work perfectly, so we'll see.

 

[Kell]

Arrived and fitted.

Also ordered new cable and outer.

Seems to have solved the problem, but I may also look at a new chain pusher as I think this is fairly worn. You could slice stuff with it now.

After taking the old one off, there was definitely not as much push in it. The new one was much more fiddly to fit.

😜

 

[Kell]

Also, this is how worn the chain tensioner was.

View: https://youtu.be/8O5NcDeyDu8

 

[berlinonaut]

I may also look at a new chain pusher as I think this is fairly worn. You could slice stuff with it now.

View attachment 665508

The Brompton Ninja Brigade uses old chainpushers as weapons - very deadly affair.