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 Post subject: Re: Rear radius arms
PostPosted: Fri Oct 27, 2017 5:11 pm 
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Joined: Mon May 11, 2015 4:16 pm
Posts: 102
Location: Scotland
Peter Laidler wrote:
Thgat's interesting dearg. Quite how on earth they broke - presumably sheared - the almost 1" dia shafts is anyones guess, even if it was mild steel!!!!!


Peter,

The outer support brackets also received attention. These were double plated. The standard ones just couldn't take the punishment. To me this suggests that the shaft failure was probably at the threaded outer end. Using a none drilled shaft would surely have increased the reliability of this portion of the shaft.
David


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 Post subject: Re: Rear radius arms
PostPosted: Fri Oct 27, 2017 7:36 pm 
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Joined: Mon May 07, 2012 6:10 am
Posts: 2462
Location: Big Red, Australia
Dearg1275, it sounds like the outer end was breaking?

Can't say I've heard of that, but I'm sure if it could be broken, those guys did break them :o

The Inboard ends do break off, not the main part of the shaft, but near the shoulder where the dia is reduced for the threaded end.

This in part, is why the shafts can't be hardened through.

I'll post up a photo shortly.


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 Post subject: Re: Rear radius arms
PostPosted: Fri Oct 27, 2017 9:42 pm 
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Joined: Mon May 11, 2015 4:16 pm
Posts: 102
Location: Scotland
Spider,

Your reference to the inner threaded end breaking concerns me. If the proposal is to drill this end and supply grease to the inner needle roller this way, is that not weakening the threaded end? The works team were clearly moving away from the central drilling to gain reliability under extreme conditions. If it is only a matter of reducing wear and extending the life of the shaft/bearing then it is probably not a problem but it may be a problem if subject to constant extreme use.

D


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 Post subject: Re: Rear radius arms
PostPosted: Fri Oct 27, 2017 10:04 pm 
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Joined: Sat Jul 15, 2017 5:35 pm
Posts: 513
Location: Abingdon Oxfordshire
I wouldn't let it concern you too greatly Dearg. It's like pretty much everything in the mechanical world - and not just the mechanical world either - . It is the best compromise between several things. While I don't have the facilities to shear load to bend or fracture a shaft at the start of the threaded end (is it 9/16"?, ain't got one handy.....) any more, you can imagine the tonnage required. And even a met. lab test like that is not a true or realistic trial of what the car might be subject to. More to it than that of course..., inertia and all that stuff. And think about it......, the other end has been bored across that point with a thin hole since pontius was a pilot


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 Post subject: Re: Rear radius arms
PostPosted: Sat Oct 28, 2017 12:48 am 
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Location: Big Red, Australia
Drilling a small hole through it for grease won't weaken by anything that matters.

Here's a couple from the collection, caught just before they broke off

Image

Image

Peter, the ends are 1/2"


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 Post subject: Re: Rear radius arms
PostPosted: Sat Oct 28, 2017 11:13 am 
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Location: Abingdon Oxfordshire
That's a classic Spider........ what careful tech authors would call '...point of commencement to crack' instead of just saying it as it is!

The interesting point to me is that it's bent/cracked at the reduction point but also bent at the start of the thread, as if to return the threaded part to parallel with the main shaft. You can imaging the shear loading at that point to make that happen - but it didn't shear. I wonder if a radius at the arrow/crack point would prevent this. After all, that's standard good engineering practice AND the thrust washers are actually countersunk at that point as if to allow for this. But while it's a good discussion point, it's beyond the scope of our rebuild. Food for thought is anyone was making new high quality shafts for hard use


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 Post subject: Re: Rear radius arms
PostPosted: Sat Oct 28, 2017 12:01 pm 
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Location: Big Red, Australia
Cheers Peter.

I don't tend to mince words in the way some authors write volumes, when one can just say 'It's a poor design' or what ever.

I did say 'caught' with the two that I've posted up here. By Caught, I meant caught them just before they did shear and yes they do. I'll see if I can find the photo,,,

Tonnes of force needed to do this yes, absolutely. In this regards, I'll point out / remind you that the rear swing arm is on a 5:1 ratio to the rubber cone and it's all via these pins.

Put 200 kg in the back (2 fat birds as they say) and that's 100 kg on each pin + the static weight of the car. So there's 500 kG + static. Then drive on the wonderful roads that are about & refer back to those graphs I posted a few weeks back and it does well get in to many tonnes. If you were to also add to that lowered shocks, when the rubber cones bottom out on the subframe, it gets well in to the 10's of tonnes.

As you've noted from the double bend, it is clearing a shearing action.

The Pins I've made I put a 0.020" radius in to them and I've found that quite adequate.

<Edit: Sorry it's not the best photo (not mine and part of a bigger photo)

Image >


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 Post subject: Re: Rear radius arms
PostPosted: Sun Oct 29, 2017 2:53 am 
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Joined: Thu Jun 24, 2010 11:55 pm
Posts: 973
Location: Tasmania, Australia
I broke a pin in a the Moke once, but it took three, not two, and a very large pothole.

Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian


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 Post subject: Re: Rear radius arms
PostPosted: Sun Oct 29, 2017 6:35 pm 
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Posts: 513
Location: Abingdon Oxfordshire
You nailed it Tim and Spider. I bet there's a few civil engineer types reading this and recalling their student notes regarding levers and fulcrums - and clock/anti clock moments about an axis. This thread and subject are great (if nerdy.....) examples of the fulcrum point changing when the car hits the deck hard and it suddenly switches. If I was still teaching I'd be using this as one of those good everyday examples.


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 Post subject: Re: Rear radius arms
PostPosted: Sun Oct 29, 2017 11:41 pm 
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Joined: Thu Jun 24, 2010 11:55 pm
Posts: 973
Location: Tasmania, Australia
The trailing arm in the moke is a couple of inches longer than a Mini one, so I assume that increases the leverage on the pin when the three chicks drop into the pothole.

Tim

_________________
1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian


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