Drive shaft failure

Post by **Ben** » Mon Dec 13, 2004 10:41 am

After having to fit a new half-shaft in France to continue southwards towards my goal of northern Spain, I decided to keep hold of the shattered spline. Now in my final year of a Mechanical Engineering degree at Exeter University, I am conducting a case study on splined shaft failure. The conclusion we have come up with on the moggy drive shaft after extensive testing and analysis is that it broke because they are crap! The material used is not remotely hardened, and is of very low quality in the first place. Unfortunately, we can only speculate as to the method of manufacture at the moment. If anyone can shed any light on how they were made, I would be very grateful.
Secondly, any information on the processes used to harden the retrofittable shafts would also come in handy. Apart from anything else, I'm scared of using any more than about quarter throttle now, and want some decent shafts!

Post by **rayofleamington** » Mon Dec 13, 2004 11:08 am

I'm scared of using any more than about quarter throttle now, and want some decent shafts!

I have used and abused every moggy I had (seriously abused some of them) with no broken halfshafts. Basically they were designed to cope with the engine torque, so if they last the best part of 40 years then why would you be scared to use full throttle??
I'm sure you've come across S-N curves at uni, therefore if you try and estimate the numbers of millions of load cycles the half shaft has been through (including every pothole and speedbump, every take up, every gear change, every reverse gear take up etc..) then you may not think they are quite so poor.
The risk regarding hardening the shaft is that you are more likely to get fractures, where on a softer shaft you just get a bit of yielding. Obviously every little bit of yielding adds up to a failure eventually therefore you have to make a compromise in the properties somewhere in between.

Post by **Cam** » Mon Dec 13, 2004 11:12 am

I used standard shafts (probably 30 years old) when I installed my 1380 and it coped with 70 odd BHP and some pretty aggresive driving! I broke a leaf spring but not the half shafts!

When I went up to 120 BHP I changed the axle for a Ford Escort one with RS2000 half-shafts.

Post by **Relfy** » Mon Dec 13, 2004 11:14 am

Ben, As a matter of interest (I dont know anything about them) how many moggy half-shafts have you tested to form your conclusions? And where did they come from?

Post by **Kevin** » Mon Dec 13, 2004 12:06 pm

As the others say Ben you are getting worried about nothing as Moggies are not renowed for snapping halfshafts I bet if you asked on here they would be few and far between, in fact I cant remember when someone last posted a broken half shaft on here.

Post by **Multiphonikks** » Mon Dec 13, 2004 12:10 pm

Well, I'm surprised.

I have heard of halfshafts taking 1275 power through standard boxes before. - was the car a standard setup?

I know the halfshafts have a "folklore"reputation for breaking, so I wouldn't be surprised that they aren't all that strong. I think these days most people who want a more robust driveshaft go the Marina/Escort route if they don't mind forgoing the whole standard look/feel thing. I know there were several companies who made/used/raced hardened halfshafts in the 90s. Minorite comes to mind???

I may of course be wrong - but as someone who is contemplating some power increases for her car when the rebuild starts, I'd like to hear your findings.

Nikki

Post by **simmitc** » Mon Dec 13, 2004 1:00 pm

I agree with most of what's been said. I've driven 8 different Moggies over 20+ years (still own / drive 4) and have used them all for towing (some quite heavy) and daily commuting; covering about 20,000 miles per year. In all that time I've managed to break one half shaft, and that had covered about 180,000 miles. I regard that as an acceptable risk; but would still be interested in any findings. Good luck with the research.

Post by **ericwork** » Mon Dec 13, 2004 1:05 pm

Well I had one go once, many years ago, but it was given a very hard time. It was in my pickup which had a huge amount of weight in the back, my brothers moterbike, plus engines, wheels, etc. It was just after some traffic lights turning a corner and going up a hill, so the need for a fair amount of power to climb the hill with most of the load on one corner. and finally it was my brother driving, he has killed so many cars and bikes he really shouldn't be allowed to drive. He has just bought a Lotus Elise, i give no more than a few months. I replace both shafts from a midget, as a friend had just bought a whire wheel kit and no longer needed the original half shafts. All the other moggies, cars and travellers have never given any problems.

Eric

Post by **Cam** » Mon Dec 13, 2004 1:13 pm

The Birmingham Minor centre do hardened halfshafts if you are thinking of upgrading, Nikki.

Post by **Multiphonikks** » Mon Dec 13, 2004 2:17 pm

Cam wrote:The Birmingham Minor centre do hardened halfshafts if you are thinking of upgrading, Nikki.

Hi Cam -

It's not a plan YET... but I am thinking (if things go well in the next few weeks and my partner manages to land a job she's chasing working with a certain F1 Team then) we may have the money to completely strip Hebe and start again. Should that happen, then the hardened halfshafts are a possibility, along with a slightly larger engine

<p>
I guess a girl can dream eh?

Post by **rayofleamington** » Mon Dec 13, 2004 2:46 pm

my partner manages to land a job she's chasing working with a certain F1 Team then) we may have the money to completely strip Hebe and start again.

Well - you'll certainly have plenty of free time on your hands - did she tell you the average working hours of an F1 team?

(I'm only bitter because I only got as far as the final shortlist for an F1 job)

Post by **Kevin** » Mon Dec 13, 2004 4:38 pm

Ray how come you have suddenly got a free car, I thought you were cutting down

Post by **Relfy** » Mon Dec 13, 2004 4:46 pm

Its Sid. There was too much for me (being ignorant and, as yet jobless) to do as a first project. But he will be excellent for somebody!

Post by **Willie** » Mon Dec 13, 2004 6:20 pm

BEN, as had been said the Minor half shafts are quite capable of
handling the normal loads on a Morris Minor, the problem is that
most of them have probably done many many thousands of miles
and everything wears out eventually. When you are checking the
condition of the shafts you can see the wear ridges on the splines
and if they are pronounced then look for less worn examples. The
Wolseley 1500 and the Riley 1.5 cars used EXACTLY the same
half shafts with no problems. Age catches up with all of us!!

Post by **Peetee** » Mon Dec 13, 2004 10:09 pm

The halfshaft on my modified 948 failed at the splines - they all crumbled off leaving a pointed end to the shaft. My limited knowledge of engineering suggests to me that the splines should have a radius or 45 degree chamfer at their base to eliminate a stress raiser (step change?). I believe Visard advocates something similar for modified crankshafts.

Post by **ColinP** » Tue Dec 14, 2004 8:53 am

Nikki,

I now have a vision of Hebe - with a "spare" F1 engine, customised with the wings and wheels "borrowed" from the F1 team......

Scary. You'll have to re-paint her British Racing Green!

Colin

Post by **rayofleamington** » Tue Dec 14, 2004 9:22 am

Scary. You'll have to re-paint her British Racing Green!

or Red-Bull racing green?

Post by **johnm** » Wed Dec 15, 2004 10:12 pm

I've always believed that Moggy half shafts were vulnerable and I've had three go on our traveller over the last twenty years. (Mind you two teenagers learning to drive in it might have been a contributory factor)

For high performance models (spridgets Riley Wolseley etc) there was a version that was treated the process was called "tuftriding" and they're still available AFAIK.

More here http://www.ttigroup.org.uk/nfdefault.as ... header=yes

Post by **turbominor** » Thu Dec 16, 2004 2:03 pm

out of 6 minors that have been mine I have only broke 1 half shaft and that what on the original turbominor with 100+ bhp when i booted it out of a junction towing a trailor and the wheels kept loosing and getting traction and bang! When it was stripped it had broken where the splines meet the smooth part of the shaft. But that car had been raced, rallied and generally abused + living on a farm and a far share of towing way too much

on a standard car it must be a poorly made halfshaft. My current minor with 80ish bhp is been driven flat out all the time on standard halfshafts.

Onthe Riley 1.5 subject a chap in broadway has a 1800'b series in his riley 1.5 with the standard axle and it is still going..

Post by **plastic_orange** » Thu Dec 16, 2004 5:17 pm

When running my full race MGB engined MM series with Riley 1.5 rear axle a good number of years ago, I've lost count of the number of diffs and halfshafts I've broken (used to take spares when I went on holiday). When my race engine exploded, I replaced it with a relatively standard one, and fitted minor halfshafts to it (run out of riley parts) and never broke one - obviously they had not suffered the same wear as riley or wolseley ones due to an easier life with a smaller engine, so there was more residual strength left in them. My wifes minor - mildly tuned 1098 had a riley diff in it (surprisingly) and one day this exploded and the teeth went through the casing - result new axle. Despite this being well thrashed, never broke a halfshaft.
Having fitted a Capri 3 litre axle to the MM, all axle problems stopped, and I would recommend this or a MK 2 escort unit as a relatively straightforward swap.