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

[themoudie]

I have been using the forum search to try and find some specific information about a developing intermittent problem that I am having with 3rd to 4th and 4th to 5th gear selection on "upward" changes. So far this fault is only occuring intermittently if the gear is held or accelerated in. Changing down a gear and then changing up again after accelerating is the only way to make the selection and it may take one, two or three attempts. When succesful, the gears engage smoothly and there are no nasty noises. I "feel" my way through a gear change, so can sense when the gear is fully engaged, before applying the power. Unlike some racers, who stamp their way up and down through a gearbox and wonder "Why?" they loose teeth, trash the clutch, or both! There are no problems with downward changes in the gearbox, or upward changes between 1st, 2nd and 3rd gears.

Bearing in mind that the component parts in the gear cluster and gear change mechanism have now covered over 80K miles, I am suspecting that the shift forks width will have been worn. They were built up with stellite rod and scraped, after the 5th gear on the output shaft, shed 5 teeth, back in 1977 and was replaced with a new gear. At the same time the dogs were undercut to 5°, if I remember correctly.

Motoscrubs_thread_"transmission+shimming"

Before I start dismantling the engine to see what is going on, does anybody have any theories as to "Why?" this inability to change up from 3rd to 4th and 5th gear may be happening? With the combustion side of things now nicely settled in, I'd prefer not to split the cases, but suspect delay might not be a wise option!

Some dimensional tolerances for the selector forks, the guides they run in on the gears and shimming tolerances for all associated components including end float of the individual shafts would be very much appreciated. I have both the Clymer and Haynes workshop manuals, along with a Clymer reprint of a narroiw case factory manual. But, none give any specific wear or running tolerances. Neither does Mick Walker's "restoration" paperback.

Thank you and good health, Bill

[ranton_rambler]

If it’s only up shifts, is it worth trying to tweak the eccentric adjuster a little?

[Duccout]

Bill,

Has this only happened since your problem with the clutch exploding? I wonder if that caused some other damage to the gearbox, possibly bending a selector fork shaft? It is a bummer.

Colin

[Jordan]

Bevel Ducati gear selector system is pretty junky.
It helps to develop a technique whereby you keep pressure on the pedal until the clutch is fully released.
Good idea to adjust the fork centralising cam for best position. Just move it ever so slightly in any direction, ride test to see if it gets better or worse, etc.
Gears dogs are undercut from standard. They are prone to rounding off, tolerable to about 1/3 width then junk.
Any new undercutting could remove existing case hardening so any improvement might not last very long.

[themoudie]

Good morning Ranton Rambler, Colin and Jordan,

I don't think tweaking the adjuster will solve the problem, as it only happens on upward shifts between 3rd to 4th and 4th to 5th, and then not in a predictable pattern. No problems coming down through the gears and none on upward shifts from 1st to 2nd to 3rd or finding neutral either from 1st or 2nd gear.

I "feel" my way through a gear change, so can sense when the gear is fully engaged, before applying the power. Unlike some racers, who stamp their way up and down through a gearbox and wonder "Why?" they loose teeth, trash the clutch, or both!

So, after over 80,000 miles on this gear cluster, I don't think my technique is too bad.

It helps to develop a technique whereby you keep pressure on the pedal until the clutch is fully released.

The fault had occured a couple of times before the clutch spring post episode, so I don't think that has contributed to it.

Gears dogs are undercut from standard. They are prone to rounding off, tolerable to about 1/3 width then junk.
Any new undercutting could remove existing case hardening so any improvement might not last very long.

When in 1977 the gear dogs were undercut, this was done so that they were all a consistent angle, there was some variation in the degree of angle that meant that the full face of the dogs were not in contact with each other. So far the case hardening appears to have held out.

I think I am going to find a worn selector fork, at least, with wear and tear on other components. There have been no pieces of shrapnel in the oil or sump since the clutch post episode, so I don't think that a component has started to break up.

Wear limits and working clearances (+ or - thou or mm) would be much appreciated.

Thank you for your time.

Good health, Bill

[blethermaskite]

Bill, snap! the 350 mk3 has started to occasionally do exactly as you describe, its hard to be sure (I'm on about the fourth speedo head) but I estimate about 50k miles on mine. hard to believe but my engine has never been split so I have absolutely no idea what wear there might be in the gear set or selectors........there are no "bits" in my drained oil either or on the sump magnet, mine is changing mostly ok but I sometimes am missing 4th to 5th changes however the second prod on the lever works fine..........it must be a wear issue? I really don't want to pull my engine down over this unless it gets worse. So sorry I don't have an answer ......just the same experience
Cheers,
George

[Duccout]

Bill,

I am not sure from your post what is actually happening - is the gear just not selecting? So that when you try to change up the the box is refusing to move out of the current gear? Does it move into a false neutral?


Colin

[themoudie]

Afternoon George, thank you for your insight.

2nd and 3rd prods don't always resolve the problem, so I have to go down the box, accelerate and then try again. The problem comes having made the passing manouvre and the next gear isn't there to take you away!

I too don't want to pull the engine apart. But, getting stuck in gear, in the middle of a manouvre is not my favourite position to be in. Oncoming traffic! Or damaging other components that are otherwise serviceable.

Likely to keep riding until the next oil change and then do the dastardly deed!

A NOVA cluster would be nice! But, I don't think the cash flow would take the knock. I hope Nigel has some standard spares?

Good health, Bill

[LaceyDucati]

Bill,
As the changes from 3rd to 4th and 4th to 5th are controlled by different forks It's unlikely the issue is fork or dog related, unless you are prone to multiple wear/failures/bad luck Worn dogs would mainly show up in jumping out of gears.

My thought is, it's the selector box and there is wear in it. If it is then adjusting the eccentric should prove that, but will most likely just move the issue elsewhere in the change. Either try another box if you have one or investigate yours before you rip into the engine. Most selector issues are a result of many things adding up to too much slop in the mechanism (combined with Ducati's errors....) If you need guidance best give me a call sometime.

Regards Nigel

[themoudie]

Aye Nigel, thank you for your calming message.

I have access to two more selector boxes and will dig these out and give them a whirl. As you suggest I will see how much "slop", a nice technical term, I have in the current selector box and will contact you for parts.

As to my scepticism about the selector box in my earlier reply to ranton rambler and Jordon, my apologies, I will update this thread as the investigation progresses.

Good health, Bill