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Torsion bar failure

I have a french car, 99 Renault Laguna (yes I live in Europe) that has gradually sunk down onto its haunches (rear wheels). I wanted to replace the struts, but discovered it has torsion bars and shocks, no springs.

It’s bottomed out pretty well, but the shocks appear to function.

Can I drive it to the dealer, 30 min away?

DO torsion bars fail gradually, or just break noticeably? Havent really had anything happen, except a bang under the car when hitting a speed bump a couple of days ago.

Yes, they fail gradually over time, like coil springs. The bars can be ‘reset’, meaning they can be adjusted to reset the ride height. But if the spring rate of the bar is compromised, the bar needs to be replaced. I’ve had two trucks that also used torsion bars. They both called for periodic checks of the ride height and adjustment instructions for the torsion bars.

You can drive it 30 minutes away as long as your tire isn’t going to hit the inside of the fender well and get punctured by something. Just go real carefully over curbs and speed bumps and rough roads/areas.

I agree that it should be replaced. Tortion bars that are tired can break.

Since the “settling” was apparently gradual, then the torsion bars are probably not broken.
However, I can tell you from experience that it is possible to break both torsion bars simultaneously. Many, many years ago, a friend of the family was driving his '58 Chrysler (too fast, probably) over a rough RR crossing. With a very loud BANG, both torsion bars broke and the car came to an abrupt halt.

Since the '58 Chrysler products were a true disaster from a quality control point of view, I have no doubt that the steel for those torsion bars was not properly tempered during manufacture, but still, it is possible to break torsion bars by merely driving over rough terrain.

As was said, it is very important to make sure that the tires are not rubbing on the inner fender liner.
If they are, then you will need to have the car flat-bedded to the mechanic for repair.

The “bang” may have been a torsion bar breaking. Or maybe the weak torsion bars allowed the suspension to bottom out. If the car is bottomed out all the time something may be broken.

Torsion bars slowly lose their original torsion, and the car will sag a bit, but the bars can be adjusted.

I remember having the front torsion bars adjusted on my '63 Dodge Dart to correct the ride height.

Drive slowly and carefully to the dealer.

Thank you all so much for fast and informative replies. The back end has indeed sagged gradually more and more. The noise a few days ago was a sharp metallic sound like something snapping, I thought at first a steel object had bounced up off the pavement and hit the bottom of the car, but there was nothing lying in the road. Since then it’s much lower. I’m puzzled by the total symmetry of the way the car looks, while the sound I heard was definitely one single pop going over that speed bump.
Car parts are hard to come by and heavily taxed here in Norway, so anything that can be adjusted is good news. (Of course car mechanics charge about $100 an hour too, but still.) Environmental laws designed to keep people on the train).My Chilton manual says keep hands off the rear suspension due to the need for special tools and adjustments.