Sudden brief lockup and no idea why

[Sannox]

Hi all, hope you're all getting back on the road ok. I was out earlier today and had a very unexpected lockup while setting off onto a roundabout, it felt like both sets of brakes snatching on then releasing though I had no tyre skid, it also felt, worryingly, like a transmission lockup and I'd say that would be a more accurate description, the front didn't dive like it would if the front brake suddenly locked on, I was in 1st and only doing maybe 10mph. I was a bit confused, a few miles later, heading home after a visit to a shop, it happened again, this time at about 30mph and was a sudden jerk/shudder, I pulled the clutch and released it, carried on till I could pull over and check the bike, all seemed ok, happened a third time and I limped home at 30, not wanting to go faster and it did the 10 miles home ok. Not long had new tyres, fitted the wheels myself and done this every time I've had rubber fitted over the 10 years I've had the bike, so I know there is no issue there, I double checked anyway. I had the front sproket cover off having previously had the front sproket nut decide that it didn't want to stick around any more and is in some French field near Saint Quentin, no problem there, the upgraded nut is still in place and tight. Chain tension is fine, having not long fitted the rear wheel on (100 miles ago) I put the bike on the centre stand and had it running and in gear, tried 1st, 2nd and 3rd, no problems, some slight rear chain lash, but nothing I wasn't expecting. Any thoughts on this as I am totally stumped, been riding since I was 16, 52 now and not seen anything like this.

[agricola]

 Id be looking at wheel bearings/chain/sprockets/alignment of chain/chain tension etc first

[Sannox]

First place I looked was the chain/sprocket setup, all good there, wheel bearings are fine, front were replaced with OEM 10k ago, no issues with rear bearings

[Gnasher]

As you've removed/replaced the rear wheel recently, check the rear wheel spacers, brake bracket and brake torque arm are correctly fitted.  Then check the rear caliper making sure you've got the pads/discs correct, it's possible the pads are not either side of the disc and the piston is binding on the discs. 

I've seen the above many times over the years, I kid you not.

[Sannox]

All good there :-) I've double checked all the wheels, alignment, brakes etc

[agricola]

Long shot: tyres not loose on the rim is it?

[darrsi]

Is the clutch cable adjusted properly from the top AND the bottom?

[Sannox]

Tyres fitted by M&P and watched them do it, all fine there, clutch cable is fine too, pulled in the clutch each time it locked up, my next port of call is to drop the oil and check for swarf and also take the clutch cover off amd check all in one piece.

[Gnasher]

pulled in the clutch each time it locked up,

When you pulled the clutch in did the bike run free, i.e. no trace of any lock up?

[Sannox]

Yes, the bike 'unlocked' if you like. Will have a look Sat at the clutch basket, see if any springs broken, check the clutch plates etc, take it all apart and all that.