CB400 gets stuck changing gear

[SarahMac]

Hi All,

I own a '93 CB400SF. I recently started having problems changing from 1st into 2nd, the gear lever would 'stick' and I'd be unable to move it at all, engaging and disengaging the clutch and attempting to wiggle the gear lever would eventually release it and then I'd be able to change gear fine. Obviously not an ideal situation!

I did check the obvious, clutch cable, didn't seem to be a problem with it. So I'm now at the stage where I've removed the RHS crankcase cover and the clutch and am examining the gearshift linkage.
With the bike on a paddock stand and the drum shifter removed (see pics below) I am able to turn the shift drum centre by hand and change through all the gears with no problems (sometimes need the rear wheel turned a little to get them to click into place, but I think this is expected?).
However, when I then reattached the rest of the gear shift mechanism and tried to change using the gear lever, some of the times it got stuck! The stopper arm was not properly in the grooves and the drum shifter seemed to be stuck out of position, with no play anywhere in the system. As before, trying to wiggle everything and turning the back wheel eventually released it, but it hadn't changed gear.
None of the parts involved look obviously worn to me, but I'm not really sure what I should be looking for. So basically, my question is, has anyone experienced this kind of problem before? Are any of the parts involved known to wear and need replacing? Can you give me any advice on what I should be looking for in there that could be a cause?




Thanks in advance for any help/advice/suggestions!
(If it would help I can take some photos of the actual parts tomorrow and post them)

[royster81]

Hi and welcome,

Not 100% sure of your fault but I'm a believer of check the easy things first,

is the lever moving freely on the footrest?

Are the joints at the end of the gear shift shaft freely moving ?

[SarahMac]

Thank you :)

Yep, the joints all seem fine. We have also tried changing gear with the gear lever detached, just turning the spindle by hand and still experienced the problem. So it doesn't seem to be an issue on the gear lever side. I almost wish it was, I like simple solutions!

[JulianBoolean]

Sadly it sounds like a bent or worn selector fork.

[dobbslc]

I would say it's worth pulling out the shaft no3 in that pic and cleaning it.
Clean off all the crap you can before pulling it out or you'll knacker the oil seals .
It could just be gummed up with old chain lube.

[dobbslc]

Also check it's not bent and give it a bit of grease before putting it back in.
The shift from 1st to 2nd has the longest movement so check if anything is catching at its furthest throw inside the clutch cover.

[Superjack44]

Might seem a bit of a silly suggestion but how long is it since your last oil and filter change ?
My vfr800 gets problems with the gear change with some brands of semi synthetic oil.
I know they are different models but it could be a cheap solution just by changing the oil and filter.

[SarahMac]

Cheers for the replies :)

It is starting to look like I might have to accept that it's a selector fork problem. The only thing that's making me doubt it is that I can change gear no problems by turning the shift drum (pt.21 in pic) by hand with the rest of the gearshift linkage detached. And I'd like to eliminate all other possibilities before playing with the gearbox!

I would say it's worth pulling out the shaft no3 in that pic and cleaning it.

Took your advice and did that today. Apart from the end that sticks out the LHS, which was filthy, it was pretty clean and seems straight. There also isn't anything that it's catching on. But I'm a bit confused by

The shift from 1st to 2nd has the longest movement so check if anything is catching at its furthest throw inside the clutch cover.

because as far as I can tell the same amount of rotation is needed to change between any two gears.


I haven't changed the oil filter since I bought the bike last winter (I plan to do it now since I have the bike drained anyway!), but I have done regular oil changes. The most recent one was in France, with a brand unknown to me, a few weeks before I started experiencing the problem. So definitely a cause to eliminate by going back to my usual oil now I'm home, thanks!

[dobbslc]

First to second has to go through neutral as well so normally it's got to travel a bit further.
As for the drum, if it's rotating and changing gear normally without any of the shift gear attached then it's ok I would say.
Can you take part the little pawls and see if there's any grit or debris in there? Parts 10,11,12,13.
If something is burred or worn in that area it will stick.

[SarahMac]

As for the drum, if it's rotating and changing gear normally without any of the shift gear attached then it's ok I would say.

That's what I was thinking and hoping!

I've taken apart the little pawls now and had a look. I couldn't see anything, and none of the parts look worn.
But, I reattached all of the gear shift mechanism and had another go at changing through the gears, no problems! Still need some rotation to click fully into gear properly, but we couldn't get it to 'stick' like it was before. So I'm wondering if maybe I have dislodged some grit or dirt somewhere in the process of taking it all apart.
Next plan is to put clutch and everything back on, new oil, new filter, and test whether cleaning everything and the oil change has solved the issue.