If I buy brand new (NOS) torsion bars, can I get 2 right ones and use one of them on the left without expecting any issues?

 

ive heard that the metal in the bars is sort of "pre-stressed" to work in one direction vs the other. the splines are different end for end so it seems like they go to some trouble to mark them L/R.

that said in 2014 i put in aftermarket bars in my car and am not certain if i put them on the correct side either.

 

Checking the PET for 85 and 88, there are clearly 2 part numbers, one for the left and one for the right. They don't usually do this if the parts are interchangeable.

 

I expect the difference between left and right torsion bars is the clocking of the splines, inner to outer. This dedicated "handing" also serves as a good reminder to us that the torsional load direction should never be reversed once a load memory is established.

 

I'm aware that the PET lists left and right versions separately.
The workshop manual states that you should check for the left/right marks but does not describe any other difference.

Since I've never had these in my hands and I cannot visibly see it on pictures: what are the spline differences?
I know that there are 40 inner and 44 outer splines, but they look straight cut, so one could flip on side to the other without issues.

It's just the internets, but I've seen BS called on 'pre-stressed material' for these bars.

Please bare in mind that we are only talking brand new ones, used bars I would definitely not want to switch around! However, new ones I'm considering.

Edit: 924 WSM states that: 'Torsion bars are under tension and may not be mixed up. Their face is marked L (left and R (right).'
So it doesn't seem outlandish, that the 2 part numbers are just there to avoid confusion after load memory is established, as suggested by Gage above.
Some confirmation or myth busting would be nice, though.

 

Just some food for thought- Jag Etypes, which I am fortunate to own a few, generate a lot of angst on the forums about the torsion bars used on the front suspension. Personally, I would be astounded if the bars do not operate well within the elastic stress range and you will be fine to use the two you have as right and left. Maybe they are pre-yielded, for lack of a better word, to work harden them on the outer diameter but who really knows? Run your car down a washboarded gravel road and things will settle out pretty quickly, I suspect. I also cannot understand why there would be a difference in the splines but welcome someone to explain to me. If you have two bars for the same side (are they identified with Porsche part numbers?), install them, and if the rear of the car settles to a level profile (after requisite fettling of the splines to get a level profile) I would declare victory and move on. If you have the car dis-assembled to this level, you have the experience to understand that going back in for an adjustment is not the end of the world. As you correctly say, we are talking new steel here.

 

I agree with Harvey, however, there is one additional thought - not saying that you will move the car on, but if you use same bars on each side, that should be clearly marked on the bar so that future owners will know how to reinstall them on the proper sides.

 

Of course it matters! Like V2Rocket said, they are heat treated to work in one direction only. If you mix them up, you risk having them crack and break. Don’t be a dumbass!

 

@StoogeMoe with all due respect, how do you know they are heat treated? And without having access to the heat treat procedure, how do you know if is somehow handed? Seriously, I'm curious. I know just enough about heat treatment to be dangerous but I'm having a hard time coming up with a heat treat solution that is handed. Now I suppose you could twist them to beyond yield, in a handed fashion, and then use an annealing process but it seems like a lot of effort for anything short of a weight sensitive part like on a F1 car.

 

Not to be culturally stereotyping, but German engineers don't typically do things for no reason.
Pre-marking them, then needing to stock 2 different P/Ns, predicting future disassembly doesn't sound like something they would do either.
You won't get any real data out of Porsche on this, but there are aftermarket torsion bars available.
Maybe their tech staff would have some insight. Along with having some bars in stock....

 

How dare you question my knowledge!

From Sway-a-way…

Sway-a-way torsion bars are manufactured in the USA from ultra light tensile certified aircraft alloy steel. All bars are heat treated to the most exacting standards and ground to precise tolerances with a #12 micron finish. The overall design, manufacture and final inspection of Sway-a-way torsion bars make them the first requirement of any offroad, drag or hot street car. Replacement of the soft stock torsion bars with high performance heavy duty bars will help prevent severe bottoming out and subsequent driveline and chassis problems.

 

I had to stay after school a lot for questioning my teachers. It's the way I'm wired
OK, understand heat treatment. You heat the entire bar up to a temperature and hold it for a specified time, then depending on the metalurgy, you either quench it quickly or let it cool down gradually. The effects on the metalurgy are isotropic, to use a $20 word. I do agree with @nowanker that the German engineering mind would not assign separate part numbers casually. I'm still cautiously sceptical as to what is going on here. The real dilema is if the OP has 2 right bars, like socks, where did the 2 left bars go to?

 

Good question! Someone wound up with 2 lefts?
If they are 'handed', maybe they'll have a broken one and can speak to the importance...

I was always amazed when the parts wholesaler would have only ONE brake disc.
Happened more times than you'd think likely!

 

I'm actually in the market for a pair of 24.5 mm torsion bars. Those were optional on NA models up to 86.
New ones are more than double the price of the Turbo M030 ones, used are non-existent.

However, I found some NOS parts online, but it's even weirder, as they have _3_ right ones and 0 lefties!

 

You heat treat the LH bars by putting them in the oven left-handed and oriented N-S, the RH bars are put in with the right hand and oriented S-N.
If you mix them up, a clown dies.