450 linkage and selector box problem

[graeme]

450 with rear sets and gear linkage that doesn’t want to engage 1st, 2nd or neutral.
Or any other gear easily.
All works ok with an old heal toe lever
Also gets all gears by turning the selector drum nose with pliers as long as I turn the wheel slowly.
I’ve tried another selector box ,,, same results.
I’ve tried adjusting the eccentric adjustment but no difference.
The selector box changes ok when on the bench but I know the return spring is not the best, have ordered new one.
Pic is the linkage, I have fitted the longer lever at the foot peg no difference.
The other lever is about the same length as the lever on the selector.
Has rose ball joints at both ends that are free moving.
(Picture is too large so will post later

What am I missing ?????

Graeme

[Duccout]

Hi Graeme,

What a pain. You say that you have tried another selector box; was it complete and working on another bike? If that is the case then there must be something happening with the linkage assembly.


Cheers,

Colin

[graeme]

Yes, the selector box from my 450 Desmo which works well.
I'll try and post a pic of the linkage to see if you can see something I'm missing,,,

[graeme]

IMG_2313.jpeg

IMG_2313.jpeg

[graeme]

IMG_2313.jpeg

[Duccout]

I'm wondering if the length of the vertical operating arm on the pedal is the problem? It is much longer than the splined arm that you have on the gear shaft. I remember that the gear lever on my 900S2 had two threaded holes, one above the other for the linkage to bolt to and if it was attached to the longer one it made gear selection difficult and increased the pressure needed to change gear.


Colin

[Boxprod]

Hello Graeme, and sympathy for such an irritating mechanical challenge.
My own rearset linkage is much less handsome than yours, but it's home-made ('cos I'm on a very tight budget...) and I'm not the tidiest welder!

REARSET.jpg

I have had the same sort of problem, where the selector worked fine on its own or with a gear pedal attached directly to it, but wouldn't do the same with the rearset linkage. Given its home-made origin, I can easily blame my own workmanship, but I have found that the cause - in my case - is simple: for the linkage to work smoothly, every single part needs to rotate with minimal resistance. I needed to machine everything to that end - not too tight at the footpeg (which in my case also carries the weight of the old Conti, so needs to be secure), and I chose clevises rather than rose joints because they can be easily adjusted.
Like yours, I know the selector spring ain't great, but it does the job, and can be persuaded into reliablity. Adjusting the eccentric cam can only help to center the detent, but you know it's right when you hear the resetting click in each direction as you change up and down.
Talking of which, you can see that I prefer 1-down and 4-up.
Very good luck.
Pete.

[graeme]

Hello Colin,
The original lever arm on the foot peg is the same length as the one on the selector box.
I fitted the longer one to see if more leverage would work.
But no change.
If I can get past 1st and 2nd, 3,4and 5 are ok and change up and down as they should.
I’m dreading this being a split the cases job,,,, but it works ok with the heal toe lever.
And by turning the nose of the selector drum with pliers.

Graeme

[graeme]

Hello Pete,

I have clevis joints and will try them.
I can’t see or feel any drag or binding on the linkage anywhere.
It has to be the linkage or it wouldn’t change with the heal toe lever.
Bearing in mind the heel toe lever is longer and should have more leverage?

Regards
Graeme

[Boxprod]

One thing which my photo doesn't show clearly is the offset between the splined selector shaft and the footpeg, which means the linkage rod/tube has to be bent into a gentle 'S-bend' so that the clevis ends are square to the levers and don't bind at all. I suspect that your beautifully-crafted alloy will need to be perfectly perpendicular to the movement, and not as forgiving as my tatty old bits of mild steel strip!
I really haven't found the difference in length between the pedal lever and the selector box lever to be a problem. All the difference achieves is a bit more or less leverage/relative movement - i.e. the ratio between how much you move your foot and how far the selector box lever rotates. Many of the old-school rearsets, like the ones you might find on racing Vincents or Velocettes, had holes drilled for varying the position of the joints, and thus varying the leverage to suit individual riders.
Fingers crossed.
Pete.