Dropping out of top gear?

[someone]

I never really used fifth gear* but have recently started to do so more. But a couple weeks ago on two occasions the bike randomly dropped out of gear: the engine red-lined and I started to lose speed.

Originally I thought it was dropping out of gear completely, but it is not a situation where you have time to do anything but quickly click down to fourth to regain control to fully check what is happening. As the bike needed servicing and an MOT I mentioned this, saying it was going into neutral, but being random he could not replicate the problem to do anything about.

I was hoping it was just one of those things, and the servicing would help. But this weekend it happened again, once, although now I think it it actually just dropping down into fourth which at least makes more sense.

It has only happened after being in gear for a while. It has not happened in any other gear, although sometimes it does slip into neutral from second shortly after changing. But I have always put this down to not being firm enough with the change. If I hold the gear lever up for a second before releasing it does not happen, or after going down from third.

The bike is a YBR 125 Custom, and has not been treated too well. The original owner wrote it off somehow after around 500 miles, so it was repaired by the original dealer. Unfortunately I have then put it on the floor a couple of times myself. With rarely having used fifth gear before though I cannot say whether this is a new occurrence or something that had been waiting to be discovered. Also, I always use the clutch when shifting, and keep the chain lubed and tensioned.

Does anyone have any ideas for what the problem may be? Or have I just buggered the gearbox?

Thanks.

*I found when I did I just lost speed, but that was on little A roads and country roads etc. But recently have been using big A roads more (the type that are practically motorways except they lack hard shoulders and I am allowed on them) and with them being much faster I have found it works better for those.

[Guest]

The fact its been dropped sounds like the gear selector may have some damage inside the gearbox

[Tango]

Could be a bent selector fork. I'm assuming that the gear lever isn't bent and catching on something, stopping it from moving fully?

[someone]

That is what I am worried about, as I guess that will not be cheap to diagnose and fix. Hence wanting some idea of what the problem may be before having someone properly investigate it.

The lever moves okay though, no obstruction when lifting it. Although as I say, this specific problem only happens in fifth gear, and has been a while after shifting. The guy I took it to (someone recommended) said it all felt okay moving between the gears when he gave it a little test ride.

This weekend though I did 400 miles in total over the three days, at least 100 of which would have been in fifth, before it happened. I just cannot see any pattern to when it has happened.

[Grumpy Old Git]

Looks like you will need to strip down the gearbox - Not a difficult task but you will need new gaskets for the rebuild.

I would expect you to find either a cracked selector or slightly bent - Easy to replace (if that is the problem) otherwise the fault could be loose shaft bearings.

Before stripping, put into 5th gear.

Once you have got the outer cover off, replace the gear lever and 'give it a wiggle' and see if you can spot any play in the internals (try moving the lever as though you were selecting 5th).

If there is no obvious fault, then you are probably going to be 'outside your comfort zone' and will need to get expert advice (unless you have a 'mate' who is a motorcycle mechanic, then this could be expensive).

Alternative is to replace the gearbox (last resort) with either a new or reconditioned one (with warranty).

[someone]

All that already sounds outside my comfort zone! I have looked in the Haynes manual though to get an idea of what you are talking about and it does not seem that bad, just looking without touching really. And now I also understand what the mechanic meant when he referred to a spring that could be a simple fix if that were the problem.

It has made me realize there is something I was not sure if I was clear about before, though. When the bike drops down it is the engine, not the gear shifter mechanism. The times when it drops from second gear to neutral it literally goes into neutral and needs to be clicked back up, hence putting that down to not be firm enough. But with the fifth gear problem it is still physically in fifth gear, you cannot click up and have to click down into fourth to get back into gear. So I am not sure it is the shift mechanism at fault?

I only went out on Saturday this weekend and either unfortunately or not it never happened, despite travelling up the A23 from Brighton to Crawley in fifth. I am still trying to understand exactly what is happening though that it happening when I am prepared would help. When it first happened the way the engine red lined and I started losing speed I assumed it had gone into neutral. But the most recent it did not lose much speed so quickly that I thought it was instead going into fourth. Thinking about it more though, fourth should not go so deeply into the red line, if at all, so maybe it is actually dropping to third.

My basic understanding of how gear boxes work, with sprockets sliding to connect to another for each gear, it has not made me wonder whether whatever slides the relevant one for fifth gear is broken. This, I think, could cause them to become unlocked to drop out of gear, but then also maybe allow the sprocket to connect on the other side engaging a lower gear. Maybe it did actually go into neutral on some occasions and not on others.

Would this make sense? Even though i never happens the other way from the lower gear. Would third gear be positioned adjacent to fifth like that? It is a five-speed gear box but I do not know if the order of the sprockets is standard or varies by design.

Thanks for all the the help. At the very least if I can properly explain what the problem is it might end up being cheaper to diagnose as I fear it is going to come to that.

[eastanglianbiker]

are you sure you have been selecting the gear properly and you havent been resting your toes on the gear level when going along without realising it going over a bump your foot has knocked the gear lever?

[someone]

That is one thing I can be sure of. My left foot dangles down between the foot peg and shifter at rest so no contact at all, which is how I was taught to sit. And was also told to never leave my foot over the shifter as the sudden engine braking from accidentally downshifting can cause accidents. Besides, I tend to dig my heel into the bike for stability on corners, so my toes are usually pointing away from it too.