Miss shifting - how long will the transmission last?

[BioBa]

My SR3 is starting to miss gears when up-shifting in particular 3rd to 4th and 4th to 5th. I have the regular stick shift. No problems ever down shifting. The problem is hardly present when keeping revs down but once I rev close to red line the miss shifts increase.I have checked linkage and it is all ok. Is this the dreaded bend shift fork problem I have been reading about?

[splitpin]

Maybe, although I'd expect to see it manifesting itself on the downshift rather/or as well as the upshift.

I would start by adjusting the rod mechanism (including transfer, engine side of bulkhead) so the lever fully connects on the upshift as far forward as possible - obviously not so far as to leave you struggling to reach the lever for the downshift! - and see whether or not that effects any improvement.

And presumably you are using clutchless/just momentarily feather the throttle upshifts? With no flywheel effect on the engine, I reckon that clutched upshifts at high/max revs are likely way harder (as well as way slower) on the transmission than non-healed and toe'd downshifts.

[Ron V]

I'm very interested in this topic as well.

Currently my SR3 is shifting fine but I did let the clutch out in 2nd gear and it started to lock the rear tires. This was by far my worst downshift so far.

If the shift forks do bend what is involved in changing them?

[paulmj]

I'd be interested in other thoughts on clutch vs no clutch on the up shifts. Is it generally accepted that not using the clutch is better on the box? If so, can someone explain why? That does seem counter intuitive to me. Slower, yes. But better for the box?

[viperu]

Not relevant to miss shift but rather a preventive lecture:

http://www.hewland.com/svga/advice.html

[ric355]

paulmj said:

I'd be interested in other thoughts on clutch vs no clutch on the up shifts. Is it generally accepted that not using the clutch is better on the box? If so, can someone explain why? That does seem counter intuitive to me. Slower, yes. But better for the box?

It's not really a complete answer, but have a read of this:
http://www.hewland.com/svga/advice.html

I think the only really relevant point it makes regarding use of the clutch is that you're likely to pull the stick more slowly thus possibly wearing the dogs more. To understand that you need to realize that in changing gear the gears themselves are always meshed, and its the dogs moving back and forth with the shaft that determine which gear is engaged at any one time. You want the dog to engage as soon as possible with minimum time spent sliding across the engagement area. Note the dogs have a back cut so once engaged they can't pop out unless severely worn, hence why you simply can't pull it out of gear without lifting the throttle.

The other thing that happens if you use the clutch is that the engine speed changes at a different rate with the clutch dipped, thus possibly affecting the time it takes for the dog to find an engagement point. I think the essence of what the article is saying is that a perfect shift requires the time for the dog to reach an engagement at an absolute minimum which means a very quick tug on the stick and pressing the clutch makes success less likely.

Some pictures of gear dogs here if you're not familiar with how they work (from a random google search):
http://www.dragbike.com/dbnews/templates/fast1320_...

[phunkymonkey]

Thanks for the article link, very helpful.

[BioBa]

At the moment with my sickly gearbox up shifting without a slight and quick depression of clutch in particular when reving high will often result in a miss shift. Today I had a very painful sounding shift problem when 5th gear would not engage and the the gearbox made very unhealthy "klonking" noise and it took quite a while to finally engage a gear.

[bloberoo]

splines on the shaft going into box ok?( check pinch bolt) and tightness/ security/integrity of engine cradle/ bolts etc.. worth a look also .

[BioBa]

Checked the pinch bolt already but have not checked engine cradle bolts - will do.
It is strange that the downshift works like clockwork while the problems are only found in the up shift. I do not know enough about the mechanics of the gear box to draw some information out of this detail.

[ric355]

I found this thread on another site which has a lot of really good pictures and descriptions on how the shifting mechanism works. There are some interesting clues on the first page which are external to the box (broken return spring for example), and a few more internal issues that could be the cause on page 5 (bent selector forks).

www.edgebuggyforums.com said:

"Note also the return spring on the gearshift cam stopper. These break. When they break you have trouble engaging gears as the cam doesn't centre and gears aren't completely meshed. This is when dogs get rounded off and gearshift forks and shafts get bent."

http://www.edgebuggyforums.com/viewtopic.php?f=9&t=4252

and

http://www.edgebuggyforums.com/viewtopic.php?f=9&a...

[BioBa]

ric355 said:

http://www.edgebuggyforums.com/viewtopic.php?f=9&a...

Great thread! At the end it still means removing the engine for an inspection.

[ric355]

BioBa said:

Great thread! At the end it still means removing the engine for an inspection.

You might be able to check for the broken return spring without removing it. If I understood the thread correctly there's a cover to remove on the outside of the gearbox.