How on earth did this happen? Never seen this before?
Who, where, when, how?
Must have been driving heavy and fast, hitting a big hole?

It looks like somting har been between the chassis and the svingarm and probally the svingarm has been reinforced.
Did he bring a new crossmember as a spare?

I have seen a lot of broken svingarms, but only two times I've seen the crossmember bended, and in these casses it was only bended a little bit.

I may be wrong, but this is quite a common failure.
The tube brakes due to torsion (fatique). Reason is the open side at the front making the tube an open section which is by far not a strong for torsion forces as a closed section.
For this reason Citroen advices to weld a U section on the back of the steering rack to create a closed section to take the load of the open part.

Clear?
Cheers, Bart

Yes but if you drive accordingly to road conditions, this wouldn't happen?

If none of the eggs were broken on the back seat after this car travelled across the very, very badly ploughed field, then the car had performed to specifications.

This only becomes a problem when the ploughed field is a long, long way from home.

Daffy Duck

Yes, obviously if you keep the car under a blanket in you garage it won't happen either...

No seriously, I think even when you don't go Red Mist.. things like these can happen.
In this case there is a pattern chassis. That might not be as torsion stiff as a good original one, causing more torsion load is put on the axle and it cracks quicker/ earlier..

Bart,
this looks to me more like a failure of the cross beam in bending.
Because the arm is mounted to the cross beam using a (relatively) friction free bearing, the load on the beam will be the resultant of the vertical reaction at the pivot and the horizontal pull in the tie rod.
Since both of those loads are being fed onto the cross beam through the bearing, there's no way that they can exert any torque on the beam.

My guess is that the resultant load would be acting as though it were trying to pull the outer end of the beam backwards and upwards, towards the passenger seat.
A possible trigger for the failure would be if the axle bolts had worked loose.
The bolted joint between the beam and the chassis would then behave as a pinned connection ( rather than a restrained one), so the bending load would be transferred onto the weaker 'open' section of the beam instead of being concentrated on the short cantileverered outer section where the bearings are mounted.

Comments on a plain beermat to the usual destination...

ken.

( Of course, if we were considering a car fitted with friction dampers and their adjustment was on the tight side, throw in a dash of loosened axle bolts, many miles of washboard surface at high speeds/loads and failure in torsion might be on the cards.)

Hi ken,
Haddened thought about it thourghly and was talking based on some quick thought and ideas I heard elswhere some years ago. Anyway


Yes you'r right, the axle can only gets a torsion load when when the whole chassis twists around its horizontal length axis.

Seams right. can't quickly think of anything else.

Although even if the bolts aren't loose the front axle will suffer from much harder load on a washboard road. Than in addition to the open bit, the holes with thread to fit the steering unit are "nice" spot close to teh edge of the opening where a crack can be initiated...

All in all, good thinking!

Broken bolts of the front axel in the dessert of Morocco. About 70km of the next village. Fun!





Broken bolts rear axel also in the dessert about 20km of the next village Figuig!