1974 450 MKIII 4th & 5th gear selection problem!

[ranton_rambler]

When I first built mine it would only change up and not down, but was resolved by adjusting the eccentric. There was only a tiny sweet spot before the problem swapped to changing down but not up. I guess that probably means I have also have a sloppy selector box?

[blethermaskite]

I am a little confused here, I was always led to believe that the eccentric adjuster on the selector box did nothing other than alter the angle of the actual gear lever at rest position? However I have always been a bit nervous of that wee adjuster just in case messing with it screwed things up........I have been very lucky that I have never had to go inside that particular box of tricks
Cheers,
George

[Duccout]

Hi George,

The adjuster screw allows the gear selector mechanism to click back into position to change to the next gear; you can commonly have a situation where the lever will select all upward changes, but not change down, or vice versa. The adjuster typically needs only a tiny adjustment to centralize the mechanism, usually on upward changes as the weight of the gear lever helps to return it on downward changes. Wear on the bush in the outer cover, and especially on the coffin spring holder creates free play in the mechanism which allows the spring to move up and down with the gear lever and prevents the detent from clicking back into place. I have had to replace the spring coffin on two of my bikes over the years in order to get rid of this free play and get the selector working again.

Cheers,

Colin

[blethermaskite]

Thanks Colin, as I mentioned earlier in this thread my 350 mk3 has in the recent past on occasions given me false neutrals between 3rd and 4th and 4th and 5th, one more light prod on the lever and the change is ok does that suggest to you wear in the selector box? I know it may seem odd after 40 years of Ducati singles but I have never needed to go into a selector box.....maybe I have just been lucky
Cheers,
George

[Duccout]

Hi George,

Those selector boxes are hideous things to work on, and very messy! In the early days of my 750 ownership, return springs would break regularly (I've no idea why) and on one holiday to Italy the spring broke on the ride down through France and I had to cross the Alps both ways without the gear lever returning; nightmare!

What I have found is that when the coffin spring holder wears, it allows the gear lever to move a small amount without engaging the spring, and this stops the detent from clicking back into place.


Cheers,

Colin

[themoudie]

I was always led to believe that the eccentric adjuster on the selector box did nothing other than alter the angle of the actual gear lever at rest position?

That is my understanding too George and virtually verbatum from Mick Walker's book ' Ducati singles restoration'.

Unlike yourself, I have been in the guts of the selector box more than once, renewed bushes and detent balls, whilst applying plenty of molybdenum grease to all the moving parts.

Today was optician day and those little dilation drops play havoc with my pupils! Rainbow effects etc., so not made any further progress.

Not only will I check the selector box, but also the end float on the output shaft of the gearbox cluster!

my 350 mk3 has in the recent past on occasions given me false neutrals between 3rd and 4th and 4th and 5th, one more light prod on the lever and the change is ok does that suggest to you wear in the selector box?

To my mind those symptoms are selector box issues and they are not the same as mine. I have no false neutrals between any of the gears, either going up or down the box. Occasionally, when I'm trying to change gear up between 3rd to 4th and 4th to 5th the lower gear will not disengage and take up the drive in the higher gear. The selector forks don't appear to be sliding the gears along the shafts and if, having accelerated, this tightens the engagement between the gear dogs. Nigel's comment that my problem involves two (2) selector forks, if that is where I have a problem, and advice to clear up selector box wear first, is why I am going down that route first. But, there is a nasty little 'brain worm' niggling in my head about the selector forks.

Hence, my request for some OME component dimension specifications and wear tolerances. My selector forks as I have already said, have been built up with stellite rod on the inner side wearing faces and then scraped, to what seemed a good working fit, back in 1977. So, I would not be surprised if their mileage has finally caught up with me.

Thursday and Friday look to be good weather days for us this week, so will go for a splash through the gutters to see if another selector box makes any difference.

Good health, Bill

[Jordan]

Could clutch drag be making the dogs difficult to move out of engagement?

[LaceyDucati]

Bill
New forks measure between 0.170" to 0.175" and I consider any forks much below 0.160" worn out (sorry for the imperial measurements!). That said it's mainly the short front fork (2nd to 3rd and 4th to 5th) that wears....mainly I think due to design/manufacture issues.

The output shaft play only effects 1st gear free play as the shaft is located by tightening into the other casing bearing onto the final drive sprocket. Everything other than 1st gear is positioned and set from there and is unaffected in function by the play.

The reason the box probably works fine in the lower gears but plays up at the top is when Ducati made the tooling to put in the extra pin in for the 5 speed box they got it wrong......Eventually they then opened up the distance between the fork claws from 24mm to 25mm on the last hinged mechanisms to fudge the original error! Add years of wear here and there and the problems rear there head again. Made properly and it would have worked fine, but with a lot of small tweaks it can be made to function well. That said the ball and dimple ident arrangement leaves a lot to be desired, hence the star cam and roller mechanism that we had made by Nova for us.

Nigel

[Duccout]

Bill,

There may be an easy way to check if your problem is selector box or internal: put the bike on the centre stand and while rocking the back wheel back and forth, change into second, then third - the gear lever should return to the central position with a loud click, if it does not, then gently pull the lever up a small amount until the click is heard. Now move the lever down to select fourth, if the lever then returns to the central position and does not click into place, gently pull it up until it does. If the gear lever has not clicked back into the central position, when you push it down for fourth it will move, but will not do anything - it will bottom out, but no gear will be selected.

Sorry if this is a bit convoluted, but it is simple in practice.

Good luck,

Colin

[themoudie]

Good morning Nigel and Colin,

Thank you for your measurements. I'm bilingual, having worked in British Imperial Hoppus feet/acres and Metric, also being of the pre '72 schooling age!

New forks measure between 0.170" to 0.175" and I consider any forks much below 0.160" worn out ....

A quick conversion for those that need it is that 0.175" = 4.445 or a rounded 4.5mm and 0.160" = 4.064mm or a rounded 4mm.

Your descriptions of "Why?" things aren't that good are very helpful and increase my suspicions about the 'short' front selector fork. However, I will still be looking at the selector box and giving it a test, using Colin's method. However, as I have rearsets and no linkage, using a reversed lever, the gear pattern is reversed as well! Sorry to be awkward! This matches the gear shift pattern of the SRX's, but on the right rather than their left. You can get discombobulated!

Good health, Bill