Differential problem V65c

I was out on the bike today, done about 200 miles and all seemed ok,
Having overtaken one of my mates, he said that my bike sounded as if it had a turbo fitted as it made a whistling noise as I went past him.??
Anyway later on I noticed a problem that had not happened previously, as I was braking on the approach to a roundabout I was changing down through the gears, and as I got down to about 1st gear as I let the clutch up with my foot still on the brake there was a crunching of gears sound I believe coming from the bevel box,
Once the clutch was out and foot off the brake, the bike was fine.
This happened maybe 2 or 3 times…
It was tipping it down with rain at this stage, so never tested to see if it was only happening when using the rear brake or not.
The bevel box has the correct amount and grade of oil.
Has anybody else experienced this, or could shed some light on what the possible cause could be…
Many thanks, for any help.

I’m not sure if your bevel box has a magnetic filler plug but if it has and it’s all gone terribly wrong then there would be evidence. Come to think of it, drain the oil into mum’s best pyrex bowl and have a good look. If there’s nothing obvious then I’d be tempted to ride gently, on my own, not in a rain storm and see how it goes bearing in mind of course that it could lock up completely!
I’m hoping that it was gear changing in those particular circumstances that caused the crunching noise.
As for the whistling, who knows? I hear whistling all the time with my tinnitus!
PS. Drain the gearbox oil as well and have a look. Can’t do any harm.

“…bearing in mind…” - well, I think here may be the answer. There are two types of early bevel boxes, one with both pinion bearings of the same size, and later, where a bearing closer to the wheel axle is substantially bigger - and for a reason. I bet this is the sound you’ve noticed, as it happened during engine braking, am I right? So, when pinion “attacks”, due to massive play in battered bearing, it settles in different angle against crown, then during engine braking it is crown which “attacks” a pinion: change of an angle, nasty sound. Yet it is dead easy to check it, as pinion assembly is a separate component together with its bearings. You just need to take bevel box apart from the swingarm(take a careful look what and in what order falls off the driveshaft), and what you then need is to separate that steel plate in which the pinion rotates. You make no harm, no change to bearings clearance/set up.
You may want to take a look at the second half of the pics in here to get an idea, I did sort of tutorial when doing minor job on bevel box: https://photos.app.goo.gl/cJxb8fTVaPphs9dB9

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Happy days.!!
Only last night got to start stripping the back end down due to being on shift work.
Drained the gearbox and bevel box of all its oil, and never found any nasty pieces of metal. :thinking::thinking:
Got ready to take the rear wheel off, removed the brake calliper, and one of the brake
pads had worn down to the metal, which was what was making the noises.
At no point did I think of the brakes, as a new calliper and pads were fitted about 6 months ago.:confused:
Pouring with rain, and not hanging about (initially) , I really thought the noise and judder was coming from the box…
Anyway stripped, checked, new pads, brake system bled, test rode the bike, and all was well,
Many thanks for your help…

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Hold on, new pad eaten in six months? Looks like caliper piston is seized. Have you made it moving again?

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It was a brand new calliper.
Yes all seems to be working fine now,
Pad was only worn on one side of the disc,
Maybe some air was left in the system. .?
But I thought that the brakes worked well, for a Guzzi…:wink:

I’m glad it wasn’t a too big or expensive outcome and thanks to adamigo for that excellent post on the bevel box(s). That’ll come in handy for a lot of people I think.

PS. I’ve just read your post again - ‘Pad was only worn on one side of the disc’. This does point to a seized piston as adamigo said. Air in the system causing this? Doubtful. Worth keeping a close eye on and …Guzzi brakes are no better or worse than any other in my opinion. Infact when Jap bikes were using sliding calipers, Guzzi were fitting dual piston Brembos. It’s easy to negatively judge an old bikes brakes when infact they’re just worn out and in need of attention.

If its a sliding caliper, its the caliper that’s seized on its sliding pins, not the piston…if the piston had seized, you’d have no brakes at all. Remember, in a sliding caliper brake, the piston “pulls” the caliper pad onto the disc, as well as pressing the piston side pad onto it.