yielding torsion bars ?

[trond]

After changing rear torsion bars to 26 mm on my SC and setting height some years ago I have found the car has sagged more than 1 inch, and now I need to re-index the torsion bars again. What causes this ? Poor quality torsion bars ? Is that even possible ?

[Bill Verburg]

Originally Posted by trond

After changing rear torsion bars to 26 mm on my SC and setting height some years ago I have found the car has sagged more than 1 inch, and now I need to re-index the torsion bars again. What causes this ? Poor quality torsion bars ? Is that even possible ?

Sound like poor metallurgy to me, I'd( Actually I did) get new drilled Sanders

[eastbay]

Gas shocks or hydraulic? Gas shock dropout over time is generally around an inch or so.

[chrismorse]

Over the years, I've seen numerous references to "settling". Some attribute it to the T bars, others to "gas" shocks, others to new rubber suspension bushings.
So, the big question is "How Long" is prudent to revisit the cornerweight and re-alignment on a full suspension overhaul??
Do the pro shops doing a lot of porsche set ups make any allowance for this settling???

[trond]

New Bilstein Sport shocks at the same time as the TB. And polybronze bushings. so bad metallurgy or reduced gas pressure then. I am happy with 26 mm TBs on my lightened SC otherwise I would replace them

[Bill Verburg]

Originally Posted by trond

New Bilstein Sport shocks at the same time as the TB. And polybronze bushings. so bad metallurgy or reduced gas pressure then. I am happy with 26 mm TBs on my lightened SC otherwise I would replace them

JMO but you should replace the offenders, creep, set & loss of tension are just the precursors for fracture

[trond]

agree, if TB are indeed changing they could fail any time. But if it is loss of gas pressure in shocks then indexing will fix it. Have ER quick change plates and could use the opportunity to get quick change bars too. 26 mm, don't want it to be too stiff. Anyone heard of newer TBs failing ? is it a common issue ?

[stownsen914]

There was a thread a few months ago posted by a guy who put aftermarket TBs in and had a failure not long after. Information wasn't clear, but seemed like a possible manufacturing defect. I think it's not so common.

On a separate point, when I had the Bilsteins rebuilt on my racecar, the front raised 3/4", presumably from the fresh gas charge. Coilovers in my case, but I expect the result would have been similar with TBs.

[Walt Fricke]

If the TBs have "taken a set" from being overloaded, you can just reindex. The bar rate isn't changed just because there is a bit of a twist in the bar. It is still governed by Young's Modulus.

That seems to have happened in my VW van when I loaded 26 4x12x1/2" sheets of drywall into it, and drove 15 or so miles (slowly) home. Those sheets weigh in at 100 lbs each. But nothing broke, then or later. It just ran a little lower than before in the rear.

Unlikely to overload a 911 like that. Especially with bars so much stronger than stock. I'd look to the other suggested causes, and consider just reindexing.