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Seized Gearbox

Diogenes

Well Known and Active Forum Website User
Non-VOC Member
[SUB]A seized gearbox is no joke and can lead to severe or fatal injuries, as a solo bike with a locked rear wheel is hard to control.

For example, see the experiences of Roger & Kay Lord:

http://www.vincentownersclub.co.uk/showthread.php?5121-Roger-amp-Kay-Lord

and also the accident of P C Vincent, described in P E Irving's Autobiog pages 358 and 364.


A seized engine can be similarly dangerous, but if the rider realises what is happening there is the chance of operating the clutch which allows the rear wheel to turn normally.

But with a seized gearbox there is not much the rider can do except look for a soft landing area.

I was wondering what, if anything, could be done to remove or reduce this hazard.

As far as I can tell, the most promising change would be to add a 'free wheel' to the rear hub.

That would allow the rear wheel to continue to rotate normally, even if the gearbox or engine seized solid.

The bike could be ridden normally to a standstill without the rider having to do anything heroic.

Only normal steering and applying the front brakes would be required.

There are many successful applications of 'free wheel' or overrunning clutch devices on pedal cycles, cars and automatic transmissions.

See, for example:

http://en.wikipedia.org/wiki/Freewheel

On the Vincent it would be necessary to abandon the drive side rear brake, and have the rear wheel drive sprocket connected to the hub through an overrunning clutch.
Not particularly difficult, though careful design and manufacture would be needed to ensure long term reliability with low maintenance.

A different riding style would be needed to cope with the lack of engine braking.

Effective front brakes [ disk? ] would be worthwhile.

But can anyone come up with a better way of overcoming the hazard associated with a seized gearbox?

I am looking for constructive suggestions, not 'reasons' why an overrunning clutch 'would not work'.


[/SUB]
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Sorry, I don't think that is the way to go, I think it would cause more accidents. I had it happen to me once = No oil in the gearbox, I checked the dip stick but did not wipe it, Big mistake. I was going too fast in third gear the two shafts locked together ie two gears at the same time, Stayed on, Don't know how !! I now check all oils befor every trip. All The Best Bill.
 

Howard

Well Known and Active Forum Website User
VOC Member
The only way is to disconnect the drive between gearbox and rear wheel when it seizes. Not sure if Vibrac's weak chain link was "tongue in cheek", but like a variety of torque limiting devices it could be set to release when the gearbox seized. Unfortunately, I suspect (without doing the maths) that a torque limiter/shearpin weak enough to protect, would be too weak to transmit full power on acceleration.
What you need is a computer controlled rear wheel clutch, operating similar to anti-lock brakes, but we're talking Vincents, not MotoGP.
Your overrunning clutch could work but it would change the bike's characteristics completely., and it's another component in the transmission train that could cause trouble.
I sympathise with Roger and Kay (and anyone else who's suffered in this way) but I think the occasional seized gearbox is something we have to accept, like stray dogs and and cars pulling out of side roads. And, no, I haven't had a gearbox seize, so I might have a different view if I had.

H
 

Robert Watson

Well Known and Active Forum Website User
VOC Member
In the summer of 1998 I rolled the Woolly past the ton in 3rd and slipped it into 4th, and rolled off the throttle, at about 95 it all went bang. Standing on the footpegs I managed to guide it from the left (fast) lane of the local piece of Hwy 1 on which this occurred and came to rest on the hard shoulder in a rather large cloud of blue smoke. The stipe was 408 feet long as the crow flies but probably 20% longer if one was to straighten it out! Gearbox was seized solid. The two gears that engage the double gear were the problem, one engaged as it should be, the other welded solid to the layshaft. Bent the layshaft, and destroyed a bunch of bits. A week later running with a Quaife 5 speed.

I couldn't imagine trying to ride with an over-running drive setup.
 

roy the mechanic

Well Known and Active Forum Website User
VOC Member
A transmission that is built correctly and contains sufficient lubrication is most unlikley to give any "troubles" I have been riding all sorts since 1964, a few motor nip-ups racing a stinkwheel(two stroke) means I still ride with the fingers on the clutch. But in all that time No 'box seizures. Maybe I'm lucky, also I built all the 'boxes myself!
 

Roger Lord

Forum Website User
VOC Member
dear Sir
Thanks for your vote of confidence obviously written by someone who doesn't know by bike and clearly likes to fling mud to see were it sticks. My gear box has given no trouble in 25 years that I have had this machine and funnily enough still hasn't. The lock up was caused by a primary drive chain failure, jamming under the clutch srocket, locking up the clutch to such an extent that we had to manufacture a puller to remove the clutch centre, basket, chain wheel and primary cover as one unit, once it was out then it all freed up. As a lot of you will know I suffered a primary chain failure a few years ago and as a result the chain, and both front and rear sprockets were new.
Just because you have suffered from no failures does not preclude someone else from suffering them and just means that so far you have been lucky. by the way are your gear selectors pins modded or standard? because their is a failure just waiting to happen, and that will either wreck the box or pitch you off

Roger
 

Roger Lord

Forum Website User
VOC Member
Hi
By the way the primary drive did have oil as witnes the pool of oil at the storage yard and my garage floor were the cover was slightly srpung and it leaked whilst waitng for the insurance to give the OK for me to start work and as I have been riding, fixing and running Vins for quite a few years I think I know how to put them together

Roger
 

vince998

Well Known and Active Forum Website User
VOC Member
Any idea what caused the chain to break again Roger?

Hope yourself and Mrs Kay are recovering well.
Hi
By the way the primary drive did have oil as witnes the pool of oil at the storage yard and my garage floor were the cover was slightly srpung and it leaked whilst waitng for the insurance to give the OK for me to start work and as I have been riding, fixing and running Vins for quite a few years I think I know how to put them together

Roger
 
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