Rear wheel lock up

[fump]

On the 4th Nov at about 100 kph on a straight highway with sparse traffic my rear wheel locked up and after unsucessfully trying to slow and control the bike I ejected. Fortunately I was wearing good protective clothing and after hiting the grass verge I bounced down a steep bank and rolled to a halt in long grass. A trip to hospital by ambulance followed and an overnight stay for observation, but damage was limited to severe bruising to my left side hip thigh and body. One very lucky man according to witnesses and hospital staff.The bike is being repaired now and it too went down the grassy slope with me and sustained fairly minor damage.
The cause was the gear box moving a little and putting strain on a bearing which flogged out and oil was lost and the box seized up. No warning signs that I could see, maybe a little more oil under the bike.

[Malleon]

I am sorry to read of your incident, Roger, and can sympathise as I also had a lucky escape recently. May your aches and bruises heal quickly, and your bike be restored to good order, too!
Best regards.

[bob]

I had a similar a good 10 years ago , when the speedo gearbox wrapped itself up .
I bounced and bruised at 55 years old , don't know if I could do the same at 65 , probably broken bones instead .
Hope you recover Ok .

[fump]

Thanks gentlemen.....yes I am ok now, though the bruising was a sight. It was lucky there was no Armco or "cheese cutter" barrier where I came off. There is in many other parts of this road. It's just fate I guess, I had just done a ride over a pretty difficult winding road and managed to not get tangled up with other vehicles or ride off the road, when a mechanical failure throws me off! I was wearing kevlar re-enforced jeans which proved their worth, as I lost no skin and did not bleed at all. The jacket took a pounding but also protected me well, as did the new boots. It certainly proves the worth of putting on all the right clothing.
I did for a while think that the speedo gear box may have been the problem as I had been talking about that with another club member that afternoon, but it was definitely the big gear box that failed.

[Rob Harknett]

Pleased you were not too badly hurt. It is a common problem, It is always a good idea to make sure the nut gets a regular check.
The gearbox can fail also a broken cable can have the same effect. Happened to me while on a Sunday run with my wife on the back.
I had noticed my speedo had stoped working, a few miles later the wheel locked up. I braked and managed to keep control and stop the bike.
Jan wondered why I suddenly stoped so quickly for no reason. The cable had wound tight on the wheel. The cable removed we continued on our way home. I replaced the complete cable then found the speedo gearbox was also wrecked.

[Colin F]

I read that you are talking about the GEARBOX (as in 4 speed thingy) not the speedo gear box on the rear wheel!

You've posted in G80 forum so I assume it's a single but you don't say which of the three types fitted it is!

Given the fairly large flanges on these boxes and the size of the engine mounting plates fitted with multiply securing bolts I am suprised that there could be enough movement to cause any thing like this without causing clutch or other problems to alert you.

Can you update us to the type of box, how far it moved and any bolts that loosened?

[Rob Harknett]

I was wondering just what was ment by gearbox, I may had wrongly assumed it was the speedo gearbox being refered to, on the back wheel.
not a speedo drive gear in a gearbox ( gear chaning gearbox )

[Rob Harknett]

Looks like this thread did get diverted a bit, having read the first message. Its was the gearchanging gearbox that was refered to.
sounds like the adjuster must had come loose, but why & how. well, I have seen some bikes that have not had 2 nuts to lock the adjuster once the primary chain has been set or if they had the 2 nuts they were not in the correct possition. One of our mates bikes was always having this sort of problem, decided to check his bike over. Alll was fine untill some time later after stopping for fuel, his bike would not come off the stand.
on checking a gearbox stud nut had come off, the stud moved , preventing the stand from going up. We said all your fixing nuts & studs are loose. He replied yes, I had hell of a job undoing them to adjust the chain, so left the nuts a bit loose.?????

[fump]

Yes it is the gearbox i am referring to, it is a 1952 Burman 4 speed box. I havn't seen the machine since the crash but the mechanic says that there was a lock nut missing on the adjuster, which appears to have allowed movement. I had no idea there was anything wrong at all, and I do ride this bike regularly. Apparently the main shaft was bent and has now been straightened and a new bush made for it. i had checked the primary chain recently and thought the tension may have been slightly on the tight side but okay and the secondary chain was fine for tension. But the box may have come loose since i checked it about 4 weeks before the crash. The incident happened toward the end of a long ride after about 160 miles, so the damage may have been done on that ride.

[Rob Harknett]

Guess the rear chain pulled the gearbox back out of line and tightened the primary chain.