I recently acquired a 750 Breva, which is ok apart from a transmission whine and some vibration. This is in all gears but stops when the clutch is pulled in. I ran it in gear on the stand and the Bevel box is quiet, the noise seemed to be concentrated in the gearbox bell housing area. I drained the gearbox oil whist warm and it was clean and there was no metal either in the oil or on the magnetic plug. In my mind this pointed to the clutch. So I have pulled out the gearbox for a look and dismantled the clutch for a look expecting to find some carnage, however it doesn’t look too bad apart from marks on the mating surfaces. My thoughts are to clean up the mating surfaces and fit a new plate. I have attached some pictures to see what the consensus is. What do you think?
It’s an odd pattern of marking on the plain plates. But I’m inlcined to agree.
To my mind having pulled down this I personally would fit a new clutch kit for peace of mind if I intended keeping the bike. However if you could clean up the steel surfaces up and fit a new friction disc, you could be OK.
I have decided to order both a clutch and pressure plate. I did find that the clutch actuating arm was nearly ceased so might not have been releasing properly. I also noticed that the centre disc that sits inside the pressure plate had polished edges where it had been turning. So it may be a combination of these two events. I will report back when I get it all back together. Trouble is I can see a lot of other refurb work now the bike is in bits. 
Such is life.
Well that hasn’t worked.
Has anyone had a gear box rebuilt by NBS? if so how much am I looking at?
Gear box removed yesterday in 2 and a quarter hours. I am getting faster at this! 
I dropped it off at Nige’s for investigation. 6 hours round trip in the car. What a place! Hopefully it is not pitted gears otherwise I may be looking for another gearbox. 
I will report back.
I have just heard back from Nige. The gearbox is scrap. 3 gears are severely pitted. One of them is over £400 on its own! On the hunt for another box now 
Any word on causation.
Lack of use? Condensation?
There was a problem with the case hardening on some of the gears on the very early bikes. I think mine was one of the first batch as it was an 03 demo bike before the last owner bought it
Can you use another small-block gearbox, or is the Breva 750 specific?
The apparently you can, but the Breva gearbox is beefed up. Luckily NBS have tracked one down for me. I should get it at the end of the month when the bike has been broken
Damn … 
Mike is that technical advice?
Chris, glad to hear you have tracked down a good gearbox.
Best wishes Chris
Cheers. I will take some pics of the damage when I pick up the old one.
Hmm, I didn’t much enjoy reading this! The transmission on my V50 II also whines and the gearchange is a bit “agricultural” - reliable enough, but it does produce some pretty loud clangs at times, particularly on up-changes. I’ve been told “they all do that” so I’ve been ignoring it, though I never entirely believed it. So, I’ll ask the question again, do they all do it or does whine=bad like it does with most gearboxes?
As mentioned earlier in this thread, the bevel box sounds quiet to me and if I run it in gear with the back wheel off the ground, the whine stops when I de-clutch. There is no audible whine in neutral. I have to say, it’s not a very loud whine, though it gets louder under load. When I first got the bike 8 months ago, I changed the gearbox oil and it was clean with no visible metallic particles, but it was a bit emulsified, as if some water or condensation had managed to get in there. That hasn’t recurred.
Comments appreciated!
Joe.
I have had a V50 in the past and the transmission was agricultural and did whine a little. I have no heard of gears pitting on V50s.
My Breva was vibrating through the footrests, but the gear change was fine.
They all do that. What mileage have you got on the box? Mine’s coming up for 80k miles - sounds as sweet or as awful as it ever did. Always oil changed on recommended intervals or so. I’ll have Nigel go over it next time it needs a return spring but I’m not expecting bad news.
My V50 whines, always has. Didn’t like the recent v hot weather, started finding false neutrals. This winter will be a g.box strip, clean and new bearings.
Steve.
Thanks guys!
I’ll stop worrying about it, the whine sounds a bit better already! Apart from the gearchange being noisy from time to time, I find it OK. I only really notice false neutrals if I’m a bit over-gentle with it, it does prefer a firm-ish prod. Sometimes it is reluctant to engage 1st when stationary, but I’ve got used to just slipping the clutch a tiny bit, when it slips in just fine. I’d call it quirky rather than faulty.
Joe.