Loud gearbox knocking

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BNStudios1
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Loud gearbox knocking

Post by BNStudios1 »

Had this issue for a while now and replaced clutch/thrust bearing and no difference - thinking it could be a bent input shaft rattling around inside the spigot bearing due to the harshness of the noise? It only appeared after removing engine for oil pump change then putting back in car...
The noise goes away as soon as a little pressure is applied to the clutch release bearing as shown:

Here is how it sounds with the gearbox cover removed:

https://www.youtube.com/watch?v=5ky1Y2mO9Ig

Any ideas?!
les
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Re: Loud gearbox knocking

Post by les »

I think you’ve proved it involves the clutch components, seems that the box will need separating from the engine to rectify, it then may become quickly apparent.

BNStudios1
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Re: Loud gearbox knocking

Post by BNStudios1 »

Had the engine out a couple of times since the noise appeared - once to replace the clutch (made no difference!) and having looked around there didn't seem to be anything out of order! Little play in the input shaft but nothing noticeable with the clutch... That's what made me think it was an issue involving the spigot bearing or maybe the input shaft bearing?!
les
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Re: Loud gearbox knocking

Post by les »

Just re read your first post, where I now realise you have since dismantled, and looked. It does seem clutch area though, I can’t see the gearbox being involved but I’m guessing now!

BNStudios1
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Re: Loud gearbox knocking

Post by BNStudios1 »

Yes pretty sure its coming from the clutch area judging by the sounds of things! I think the engine will have to be taken out again - I haven't been able to find many similar situations on the messageboard so i'll be going into it blind! All I can say is I know it can't be the clutch assembly as the old clutch made exactly the same noise as this brand new one...
Could it be a symptom of a wonky flywheel? The only thing that stops it is putting a little pressure on the thrust bearing as I said

Strange as it is a very distinct noise but once you're in there having a look around there appears to be nothing wrong! The engine doesn't make any noise when I rotate it by hand either... very annoying! :-?
les
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Re: Loud gearbox knocking

Post by les »

It will be interesting to see what you discover, good luck with it, it’s a mystery.

BNStudios1
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Re: Loud gearbox knocking

Post by BNStudios1 »

Thanks - I'll take a look again and see if theres anything I missed
pgp001
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Re: Loud gearbox knocking

Post by pgp001 »

Can you "feel" anything through the clutch release lever just before you apply pressure ?
I wondered if it could be the clutch release fingers catching the lever itself.

Phil
BNStudios1
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Re: Loud gearbox knocking

Post by BNStudios1 »

Yes you can feel a juddering through the fork when you move the thrust bearing into contact with the clutch bearing - then as soon as a small amount of pressure is applied the noise and judder fades away gradually depending on how much force is put through, until eventually it disappears completely (when a reasonable amount of force is put on the release fork)
The juddering doesn't feel like anything is catching on the fork though - it feels more like a wobble/judder transmitted from the clutch - not sure though!

Finn
kennatt
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Re: Loud gearbox knocking

Post by kennatt »

had exactly the same issue with my old 948 ser11 ,tried everything as you have and eventually just put up with it couldn't hear it once driving but then you wouldn't expect to with all other engine noise,but about 18 months later started to throw 4th gear out ,swapped gearbox and noise gone. I think it was the input shaft bearing in the box letting the shaft chatter until clutch plates grabbed it to stabilize the shaft. but never really worked out the hows any whys of it. I.ve tried to think of why it would start after your pump change but no idea except if you also had box out and stood it on the bell housing(the worst thing to do) for any length of time all the grit/ crap/ in the box has settled into the bearing and caused rapid failure . But would have thought that it would have taken a while to show up. No help really but good luck with it.
Not just wear in the fork is it ,that may cause it, to clatter taken up when clutch pressed?
philthehill
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Re: Loud gearbox knocking

Post by philthehill »

I suspect that your spigot bush in the rear of the crankshaft has failed or has fallen out when you removed the box to do the pump..
Just had a 948cc engine where the spigot bush just fell out when moving the engine. Of course it should be a tight fit in the rear of the crankshaft.

newagetraveller
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Re: Loud gearbox knocking

Post by newagetraveller »

I agree about the missing spigot bush.
There should be a rubber cover over a hole on the left hand side underneath. I think that if you take it off and shine a light in you may be able to see if anything is moving about although you cannot see the spigot itself.
(I hope this makes sense. )
oliver90owner
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Re: Loud gearbox knocking

Post by oliver90owner »

Not sure about the bush being the problem - the shaft will be rotating with the crankshaft while the clutch facings are locked together - so the shaft could only ‘wave around’ while the clutch pedal is depressed? That is unless the clutch driven plate is off-centre while driving and something is catching or shaking something at the gearbox end or release mechanism?

So I’m with kennatt on this one, although on this occasion the noise seems to diminish after taking up the clutch pedal free play. I definitely think it won’t end in a good way.

Never ever been wrong (ha ha!) before but could be on this one :D :D :D

I’ve never had a spigot bearing completely fail before - but I don’t sit with the clutch pedal depressed more than necessary, so hopefully don’t wear them out too quickly.
kennatt
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Re: Loud gearbox knocking

Post by kennatt »

if it was the spigot bush would it not work the other way,ie when clutch out no noise since as oliver says clutch mech is holding shaft steady,clutch in and shaft is now held by first motion bearing and spigot so no spigot and bush free to clatter. However would this theory apply to bearing,hmm ? maybe not since it could be the bearing that is knocking and not the shaft,when clutch pressed shaft stops rotating so bearing is no longer under pressure. Be interesting to see the result. good luck with it
philthehill
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Re: Loud gearbox knocking

Post by philthehill »

The only way this will be resolved is to first check the clutch release linkage for excessive wear - if nothing of note there then it does mean separating the engine and gearbox and examining everything within the bell housing to ensure that all is as it should be.
Unfortunately trying to give an opinion from a distance does mean that it is all a guesstimate.

BNStudios1
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Re: Loud gearbox knocking

Post by BNStudios1 »

Thanks for all the suggestions - the clutch fork did have a reasonable amount of play at the pivot, so engine has come out (again!) and replaced the bush inside the fork pivot - so that is nice and tight now.
Once again separating the engine from the gearbox showed no obvious signs of where the noise could be coming from so hoping it was the fork after all...

Can’t figure how the clutch plate could be off-centre as suggested as it is centralised by the input shaft surely?

Also replaced the spigot while the engine was out just in case it was anything to do with that (small amount of wear on the old one but nothing major) but I agree its unlikely to be that as the noise only appears while the input shaft is spinning with the spigot

Hopefully this problem was to do with the play in the fork (it was about 1/2 cm each way) but I will only find out once its all back together again! The fact that I couldnt feel any particular feedback from the knocking sound through the fork while the knocking was occurring makes me a bit doubtful, but if the noise persists once the engine is back in then I really will be confused!!
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