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MG MGA - A frightening experience

Took my A out for a Sunday drive, in the company of my wife. On my return journey home I had the fright of my life, and naturally so did my wife. As I was manouvering round a large roundabout, the right hand side (driver's side) front suspension suddenly and without warning collapsed with a very hard metal thud onto the ground. Luckily, I was only doing about 20 mph, and so the car slowed down and slid with a crunch for about 10 metres, and then came to a stop in the middle of the road. I then put it in first gear and drove it very very slowly to the side of the road. At this time I was shaking from this experience, and when I regained my composure I looked under the front wing and saw the lower end of the swivel pin (kingpin) had sheared off completely, and the lower A arm with the swivel link still bolted in place resting on the tarmac. A very frightening experience indeed. I have obviously decided to replace both the RH and the LH kingpins, but, thinking that the broken kingpin was NOT of the best quality, would anyone recommend a good source for a pair of best quality replacements.

Frank
F Camilleri

B & G have a good reputation here for their improved swivel pins. Do you know the history of your swivel pin? Have you ever had them crack tested? It would be interesting to see a good photo of the failure and results of a crack test on the one that is still in tact.
Mike
Mike Ellsmore

Frank

Thank goodness you are both ok and it happened at a relatively low speed. Apart from the obvious damage you mentioned, was the bodywork etc ok?

Steve
Steve Gyles

Frank
Really sorry to hear about that.
To give a bad experience a positive edge, when you've got the bits off and cleaned them up ('cos we all have a black museum, don't we?) can you post some pictures of the break so we can see exactly where and how it went - we all need to be aware of what to look for.
I would really appreciate that.
Thanks
David
D Brown

There were some photos posted earlier (by Mike Ellsmore I think).
People tend to think that this could happen at high speed, but it is more likely when parking the car, going around a roundabout, or rally competition.

Photo attached.


Mick

M F Anderson

Another photo.


Mick

M F Anderson

Hi guys,
thanks for your comments. Believe me it was soooo scaaaaary I almost fainted. My wife has declared that she will never again ride in the car. I guess I'll have to organise a female partner.

No Steve no other damage that I can see, only a broken kingpin. I have also decided to replace both pins left & right. I have no knowledge of the history of these parts, and to play it safe I will replace both. I have this morning disassembled the front right suspension, and as I said no other visible damage is apparent.

I would be very grateful if anyone here has any knowledge of a good source in the UK. Naturally the most important is the quality of the material. I bought most of the parts from B&G when I restored the car. I have no complaints.

I couldn't take pictures this morning, simply because all the bits & pieces of the suspension are covered in grease. I will clean them up tomorrow and some pics will follow here.

Many thanks folks

Frank
F Camilleri

Frank

I've bought stuff from these people over many years. They also know the MGA inside out.
http://www.mgbits.com/contents/en-uk/p6179.html

You could ask them about the spec of their part compared with the original, and they should be interested in your problem.

To my non-expert eye, it looks like yours (and probably mine) have a design 'problem' - a point of stress at the start of the thread, leading to fatiguing and to a crack spreading across the swivel pin. Mind you I doubt if the original designer expected so many of them to be in service fifty years on. However, it would be interesting to see a close-up of the faces of both parts of the pin.

I have to replace the rubber wishbone bushes on mine soon, and your experience suggests I should have a close look at the swivel pins while I have it apart.

David
D Brown

We need to be careful when we talk about "the original" design. I have a pair of new BMC pins bought in December 1967; their shapes at the section change before the thread entries differ from earlier versions.

Alex
Alexander_R

David I will post some pictures as soon as I can. On another note, replacing the wishbone rubber bushes should be fairly straight forward. No so with the swivel pins. But I would presume you are only visually checking the pins. I think it will be difficult to inspect them properly when they are installed. Removing them from the car is a PITA, and I wouldn't recommend it. But if you are strong and determined then good luck to you.

Frank
F Camilleri

When looking at the above photos, am I seeing casting cracks in the new part, (where the taper meets the threads), or is that dirt or a reflection?
Just looking at the way it is constructed, there are huge side forces applied to that pin....Amazing that more do not fail.
Edward
Edward Wesson 60MGA

Mick, -- In your photo showing two pins side by side (one broken), both appear to be the same design and non-original design. Notice where the end of thread cuts into the conical surface. That produces a significant stress riser that will contribute to crack propagation. Original parts have a generous radius undercut to diameter slightly smaller than the minor diameter of the thread. That radius serves as a strain relief to spread stresses over a lager area to inhibit cracking.
Barney Gaylord

The NTG swivel pin - as posted by David - would appear to be as Barney describes.

Dave O'Neill2

As promised, here are some pics of my unfortunate episode. I have so far dismantled the RH suspension and removed the broken pin. I am now waiting on the parts to arrive from the UK. I will replace the LH pin at a later date. It should be a little easier now.

Frank

(P.S.) Sorry guys my pics seem to be too large, and they won't upload. I shall have to ask my son, who is very into computers, to show me how to resize the pics. Be back. If anyone here can put me on the right track as to how to do it, so much the better, as my son lives in France, which would take a while longer.
F Camilleri

Frank, the pics need to be < 1MB size.
If you have Windows photo gallery, open up the pic, go to "Fix" and resize to almost the same size, save and it will be a compressed file.
Art Pearse

here are the pics again for your guidance and assistance

Frank

F Camilleri

another one...

F Camilleri

another picture...

F Camilleri

last picture

F Camilleri

It's interesting what causes some of them to break, and others to bend. One of mine was bent at that point and probably was like that for many years. I replaced it with another original assembly from a parts car. Glad you were okay and the damage seems to have been limited.
Del Rawlins

Del,
A lack of grease will play a major part in the failure mode.
Colin Manley

Del, thanks for your concern. Thank God only the swivel pin broke, I inspected the whole suspension area and all the bits and pieces removed from the car, and everything seems OK. My self and my better half also came out unscathed apart from the shock.

Colin, I totally agree with your statement. As I have mentioned earlier I wouldn't know the history of the life of the car, only the last seven years in which it has been in my possession. The front suspension was very regularly greased. When I took the suspension apart, the swivel pin and the links were abundantly greased, no lack of lubrication for sure.

I am waiting on the new parts to arrive to get the car back on the road. The weather here is at its best, we had a gorgeous day today and our roads were packed with sports cars and motorcycles.

Frank
F Camilleri

Colin,

I'm not sure a lack of grease would have made much difference at the point where the pin has broken.

John Bray

Hi John,
Only in as much as if the threads were dry and starting to sieze against the turning leaverage when steering.
Colin Manley

What about fitting MGB king pin assemblys? I think thats what I would do if it happened to me. I had an mgb loose a front tire once when a worn hub and spline rolled and the tire came off. The experience was much as you described. Frightening!
Steven Devine

Frank
Can you do a close-up of the circular face, so we can see the texture of the break? Maybe we can see what sort of a break? My guess is that the metal was stressed at the sharp radius where the thread starts, leading to a fracture spreading across the swivel pin. I'd be interested to know whether there is any obvious crack or discolouring to be seen. Might help others to spot the problem before anything actually breaks?
David
D Brown

Colin,

Point taken, although the steering would have been quite stiff.

John
John Bray

David I will definitely post a close-up of the circular faces of the broken pin pieces. If by doing so other people can spot the problem and avoid going through the same experience as I did, or God forbid, worse, I feel I am in duty bound to post as many pics and other info as I possibly can. Please do not hesitate to ask as many questions as you like. Unfortunately my camera has a set depth of field, impeding me from taking shots any closer than one metre from the object. Pics will come out fuzzy. However, my son has a very sophisticated camera, which I'm sure will do wonders. I can ask him to take a couple of close-up shots for me. I doubt if he will let me borrow the machine. As soon as I get the pics you will see them on this forum.

Frank
F Camilleri

Here are the close ups which I promised. I simply can't figure out how the hell the pin snapped.

Frank

F Camilleri

Another one

F Camilleri

Frank
Nice ones!
Now I'm no metallurgist, but it looks like (on your first pic) the break has propagated from about 5 o'clock on the one on the right, and has over time spread upwards until there was only a couple of millimetres of metal left, and that's when it snapped.
I could get a proper scientist on a (non-MG) forum to have a look at the pic if you think that's OK? No links to here.
Thanks - they're great
David
D Brown

Definitely a break that had been in progress for a while. You've got me seriously thinking about having mine magnafluxed prior to assembly.
Del Rawlins

I'm with David on this one. I don't know the exact starting point, but presume somewhere near the bottom in these pictures and propagating upward until the crack was 3/4 the way across before final fracture. Since the crack is in a near perfect plane I suspect it started at and followed along a line where the thread was over run and errantly cut into the shank where it should have been a smooth stress suppressing radius. I think I saw a picture of that recently, but can't find it now. Anyone have that picture?
Barney Gaylord

This one, possibly?

http://home.comcast.net/~garoncurtis/mga020212.jpg

Alex
Alexander_R

Wow! Is that a cut thread? Looks a lot like a crack, except it is in the right location to look like a continuation of the thread.

I found the picture I was looking for with the manufacturing problem. See attached picture.

Barney Gaylord

Barney:

That's the very one I had in mind, tho couldn't find it. Where was it - I was looking on the MGE board.

I notice pins from the last batch made - from the package coding entering into the stock system about 1965 - are differently machined; at that late stage in the game I would think these more likely came from a better sub-contractor, rather than as the result of a re-draw. Glad to have them just the same.

Alex
Alexander_R

Here's another pic of the break which I think might be a bit clearer. I took this shot with my own camera using the macro mode. Didn't know it had a macro mode until my son pointed it out to me.

Frank

F Camilleri

David Brown - re your last post here: Yes of course you can show my pics to anyone you wish, to obtain a professional view on the subject. Please let us know if you come up with anything of interest. Sorry David I only saw your post this morning. Good day.

Frank
F Camilleri

This thread was discussed between 11/02/2014 and 23/02/2014

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