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AndyFowler

Leyland Martian Gallery

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Regards prop shaft self destruction..

 

would it not be possible to sort without the intermediate bearing as above? that shaft is running at more than 2x operating speed of the Martians Rear prop..

 

Ive now hear horror stories of chaps getting the wrong gear on a decent loaded and this over speeding the prop witch then fail's destroying the break lines with it...

as much as this scenario would not occur to a truck in preservation 1. as we are all responsible and understand how it needs to be driven & 2. we would never be towing anything on public roads anyway.

However, Im now looking at this from 2 directions, the first to do something to the prop be it an intermediate bearing and carrier or balancing the prop for high speed operation [maybe even a re-manufactured unit?].

secondly Spring brake's conversions/additions seem available and would not take much form the original form of the truck, however as much as it looks strait forward on paper....

 

could past operators/owners advise on the above, opinions and or experiances?

am I being overly cautious a Truck that im guessing is likely to travel no more then 70-100 miles a year on public roads and at speeds of about 30mph... it's just the weight of the recovery @ 25T is a lot, most we have operated up to now is about 10 loaded and not on air brakes... sorry if I sound naive.

 

I also now have many power steering questions coming from range rover classic backgroun its pretty alien ... but one thing at a time :-)

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As I understand it, the destruction of the prop comes down to harmonics (or words to that effect); so that it really depends on the length -- and diameter -- of each span of prop, the speed at which it's being spun, any unbalance in that span, and a few other things I'm sure I've missed.

 

Maybe it's possible to balance it very very well, so that you reduce the risk of causing unhappiness... but probably not enough to give you a great deal of safety margin if you're already close to the critical speed (i.e. the point at which your underpants have a critical moment as the prop does things you would rather it not.) fairly often.

 

Making the span shorter by, say, adding an intermediate bearing and necessarily going to a 2-piece propshaft would increase the speed you'd need to spin it before you got into trouble once more; ideally increasing the speed to something utterly infeasible for you to reach.

 

The other thing you could change would be the diameter of the prop tube. Going to a larger diameter moves the critical speed to higher RPMs; hopefully high enough to make it not a problem any more.

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ive mailed http://www.propshaft.co.uk about it ive used them before as i have some funny trucks with doublehoc joints in [109"v8] and this was the initial responds :-

I am not familiar with the Leyland Martian although presume it’s a military type recovery vehicle.

Sounds like the shaft is running beyond its critical speed, if so you need some sort of centre bearing mount so that the single shaft as it is at present is split into 2 and is therefore shorter.

 

and this was the initial responds :- sounds like the would be able to sort something...

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I think that converting to a two piece prop shaft is a much too complicated solution. A new shaft with a size bigger tube AND properly balanced will certainly solve the problem and be far cheaper. Remember that the balancing can be done much more precisely now than 60 years ago and the youtube video three posts ago shows that a relatively long thin shaft can survive 9000 RPM if it is balanced right. The forces go up with the square of the speed so the Martian shaft is a simple problem in comparison. If you go to a dedicated drive shaft company you will probably be suprised how cheap a new shaft is.

 

David

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It's not the rear prop that self destructs but the three speed transfer gearbox although it could be that the vibration starts in the prop. I could drive mine flat out at circa 35mph with no problem but I have seen several with a brass plate warning of the speed restriction.

 

The rear brakes have unique actuators bolted into the rear swinging beams and it could be difficult to adapt a modern spring brake unit to suit. The handbrake uses a large disc on the back of the transfer gearbox with a mechanical link to the lever.

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ive studied the layout of the aux box it can be mishandled when cold and I think this combined with the loads put on it buy unbalanced props led to some suffering and some not..

its an interesting propblem :-)

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At Rushden show last weekend.

SAM_6298a.jpg

Not seen this one since GDSF 2009. Think used to belong to Nigel aka Hippotastic. Now under the ownership of Andy Cox.

And THE ANIMAL

SAM_6310a.jpg

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The FV1103 looks a bit different to what it did on page 1 of this thread.

 

It has gone downhill rapidly despite allegedly being stored inside but still looks complete.

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