Rear Sway Bar Snapped! Anyone Else Had This?

[gavinc69]

Thanks for all the input guys.

I didn't feel any difference in the driving but I was only driving in a normal fashion to my friends and then obviously very carefully on the way back.
I think the actual break occured whilst reversing out of his drive because its got several different cambers on it (it goes down then up whilst all so on full lock) so that was probably the straw that broke the camels back.

I need to get the sway bar sorted before June 3rd as myself and car are off to Europe for a week around the Alps (so glad it didn't break then, there's some very high drops off those mountain roads!)
Once back I will look at getting some front & rear upgraded torsion bars (they where on the long list of things to do anyway) as hopefully that may aid in taking some stress off the sway bars (although the TRG sales person did say it would be fine with standard bars!)

The car also only does 3K miles per year, so its not been caused by excessive use.

[Flieger]

After seeing that there is a hex plug welded to the bar, I have a theory that the weld's heat affected zone may have left some untempered Martensite which cracked and then propagated that crack. Proper heat treatment of the whole bar could temper the bar but was it done? Properly?

[gavinc69]

Think mine also snapped off where the weld is! Must be the weakest point.

Hopefully TRG get back to me tomorrow.

[hcoles]

I think it can be said that aftermarket part manufacturers are likely to not provide as complete an engineering spec., testing and process control as is typically found in factory parts. They probably would like to but the market will not pay for it. Some are better than others. It is not the end of the world, the part breaks you fix it or get another one and get back to enjoying driving your Porsche.

[safe]

That TRG bars looks exactly like the Tarret I bought from Elephant, just different colors.

Who exactly makes these?

[911pcars]

"...Wonder if there's been some metallurgy issues with the TRG bars?"

Hmm. Typically, post-welding heat treatment or surface treatment (e.g. shot peening)? Wasn't aware welded ends is a common practice. Most torsion bars I've seen are machined/swaged from a one-piece billet, but I don't get out that often.

No excuse at that price point to not manufacture a torsion bar properly.

Sherwood

[Flieger]

Originally Posted by safe

That TRG bars looks exactly like the Tarret I bought from Elephant, just different colors.

Who exactly makes these?

Tarret uses square ends, this TRG is hex. Other than that they are copies of each other.

[hcoles]

on the Tarett site under sway bars....

"All components are designed and manufactured to the highest quality standards, resulting in the finest and most reliable swaybar on the market."

and
"Optimized geometry for bind free operation throughout the entire suspension range of travel."

so there should be no binding issues backing out of a driveway

Given this, there must be an issue on their side, I'm sure they will be glad to replace it.

[hcoles]

Then there is this on the Tarett site. Given that these parts are generally for cars used in competition (not daily drivers), it might be difficult to test in under 30 days unless you schedule race days and parts buying carefully.

WARRANTY
All products are fully warranted against defects in material or workmanship at the time of receipt. Claims must be made within 30 days from the date of the receipt.

[hcoles]

@Mike 87 911

On the TRG website I see this picture, I'm thinking the notch is there because if just plain welding of the hex in the tube.... the weld would be a weak point and subject to failure. Does your weld have that notch on the other side?

[Flieger]

The front Tarrets are not notched like that.

[j911brick]

Originally Posted by flieger

after seeing that there is a hex plug welded to the bar, i have a theory that the weld's heat affected zone may have left some untempered martensite which cracked and then propagated that crack. Proper heat treatment of the whole bar could temper the bar but was it done? Properly?

+1

[j911brick]

Originally Posted by hcoles

Then there is this on the Tarett site. Given that these parts are generally for cars used in competition (not daily drivers), it might be difficult to test in under 30 days unless you schedule race days and parts buying carefully.

WARRANTY
All products are fully warranted against defects in material or workmanship at the time of receipt. Claims must be made within 30 days from the date of the receipt.

Many times parts don't even get installed int he first 30 days; sometimes not even for a couple years.

Why not just buy the Smart Racing bars and be done be done with it? In my opinion they are the best I have seen.

[Cory M]

Originally Posted by Flieger

Tarret uses square ends, this TRG is hex. Other than that they are copies of each other.

Actually, the TRG bars are copies of Tarett (Pelican sells Tarett).

I have had both and the manufacturing and design of the Tarett is superior. The devil is in the details: The Taretts are thicker where they should be, on the contact zones on arms and bushing blocks. There is a plug weld at the end of the bar, this is where the bushing contacts the bar so it must be smooth to reduce wear, on the Taretts the weld is complete and machined smooth on the TRG it isn't. The bushing blocks on the TRGs are double drilled to be universal, but the holes are so close together that there is virtually no material between them. The plating and anodizing is better on the Taretts. TRG uses a nut and bolt to secure the arm instead of an internal thread, the bolt can drag and get damaged. Overall I just think the TRGs are a little rougher. I guess that is to be expected since making parts like this is just something TRG does on the side and not their fulltime business.

Here's some pictures I took a while back of a rear bar:

[Plavan]

Cory is right. Much to the dismay of Ira (Tarrett Eng), TRG copied his bar. The little changes they made looks like it effected the reliability.
I'm very glad I have the Tarret units.

[Mike Metzler]

I think all of Cory's comments are right on target.

[Flieger]

Whoever designed that TRG bushing mount with the siamesed holes is no engineer, and should be fired!

[chris_seven]

There are just a couple of comments that I would add:

The first photograph showing the failure is very clear and it is due to corrosion fatigue.

When a short fatigue crack develops in a material and there is water present the crack growth rate will increase quite significantly due the the pH at the crack tip.

The 'fresh' clean surface of the fatigue crack is very active and wants to oxidise very quickly so it pulls an oxygen atom from the water and increases the hydrogen ion concentration.

If you do an experiment with a fatigue crack immersed in distilled water you will find after about 20 minutes the pH at the crack tip is around 2.5-3.0.

This acidic liquid accelerates the crack grwth and sharpens the crack tip.

I would say, looking at the photograph that there was a prior defect and the corrosion helped it along.

Looking at the later photograph of the welded part it is surprising to see that the force applied to the sway bar is transferred by the weld.

The fatigue crack will almost certainly have followed the maximum stress and putting a weld t this location is not the best idea.

If you look at a basic document such as'20 Golden Rules for avoinding fatigue failures' putting welds into regions of maximum stress would be quite high up the list.

I am not sure what material is being used but it is unlikley to be a spring steel.

I think you could make such a bar by welding but you would need to use a technique such as friction welding but it would be difficult to have the opposing ends in the correct orientation so I have come to the conclusion it is better to machine from solid.



The fatigue

[ALXinNZ]

I have broken the mounts before but never the bar. Quite interesting when it happens, especially when you are flat out comming out of a corner.

I can only imagine what it would be like at speed breaking the bar..........

[hcoles]

@Chris_seven,
Interesting I didn't know regarding the localized pH. Thanks for that.

My guess regarding roll bar design is assuming the bar surface is near some sort of fatique stress limit trying to "grab" it via a smaller diameter using a weld is likely to put one in trouble without going through considerable engineering and test. I think your comments suggest this also. This may be why the Smart Racing bars have plain ends connected by only a clamping type approach. For similar money I predict the Smart Racing system is more durable.

So far my stock bars are working for me so I haven't tested any of the aftermarket bar systems.