Lack of drive

[Duncan Grimmond]

Pulling into the supermarket carpark (just some random panic buying, we've run out of pine nuts !!!) I lost drive. All gears engage, the transmission seems to be connected, the clutch feels normal but on letting it out, initially it slipped and then totally lost connection.Walk back to the workshop and collect it on the trailer.
No loud bang or clunk, the engine starts and runs so I assume the flywheel hasn't fallen off.  The inspection cover shows the flywheel in place and running true so there seems to be a break somewhere behind that. I can engage any gear ( by the feel of it ) and the transmission aft of the gearbox seems to be continuous. With the rear jacked up there seems to be motion forward from the diff, both wheels turned the same(and opposite) directions turns the gearbox end of the prop shaft.  Rolling the car back and forth certainly turns the shaft at the front end. Is there a dog, keyway,spline in the gearbox which can be discombobulated and cause a loss or is there nought for it but to pull the engine for further investigation?

[Robert Leigh]

Can you still turn a wheel when jacked up one side only, and with the gearbox in top gear? If you can you probably have a problem in the clutch. I have known clutch plates to break. If this is the case you will almost certainly hear some crunching in the clutch area when you are turning a wheel.
Robert Leigh

[Parazine]

Sounds like a half shaft or key broken. I have seen a key break on the axle input shaft (top of the torque tube) as well.....

The drive will seem to be there, until you try and put some torque through the axle, then...….nothing.

[John Mason]

Can you lift your rear wheels ( Axle stands under the rear axle) Put chocks under the front wheels then start your engine and select top gear. Look underneath and see if the prop shaft is turning if it is then it appears the clutch maybe ok. If the rear wheels turn, slowly apply the handbrake the rear wheels should stop turning and if the prop stops spinning It will most likely be a slipping clutch. If the prop shaft still spins this indicates a rear axle problem most probably a half shaft or half shaft key failure.

John Maso

[Greig Smith]

Duncan these are very similar symptoms to our green race car in the Hillclimb 2 years ago, intermittent drive and then nothing which turned out to be a side shaft key and a hub spinning on the end of the shaft

Aye
Greig

[Duncan Grimmond]

Thanks for all your suggestions. I called Ruairidh and he suggested either a clutch failure or half-shaft key. The prop shaft was being driven so I went for the axle.
I guessed the correct side and replaced the woodruff key. I'll check the other side tomorrow.

[bob46320]

BUT, the key is not meant to provide drive to the hub ! It is there to allow the hub nut to be tightened such that the force between the half shaft and the hub taper is sufficient to provide the drive. I believed that if the tapers were very well lapped together that the woodruff key is not required - but we rarely have hubs / half shafts that meet this condition.

[Duncan Grimmond]

I didn't assemble the hub, it was like that when I bought it. I have to admit I was surprised that the powerful nut was a bit on the slack side but I did need a puller to remove the hub.
That's why I'm going to check the other side...

[spannerman]

Was the key in 2 pieces if not that's not the problem!

[Dave Mann]

I think Duncan meant he fitted a new key, the term replaced can be misleading.