Porvair

So took my 951S out to a local cars and coffee this morning and noticed a pronounced noise from the front suspension while pulling out of the parking lot. Turns out that the drivers side sway bar mount snapped in two. No idea how that could have happened and it does not look like it took a hit from anything such as road debris or from hitting one of the numerous NY potholes. Anyone ever see anything like this? Car has m030 factory suspension and Fabcar aftermarket steel arms, and I had the swaybar installed a year ago by a reputable local Porsche shop. It is a bit lower than stock (maybe 1/2") but nothing too crazy.

I'm going to contact Tarett to get the replacement mounts and ask them if they have ever seen this but wanted to check with folks on this forum as well.

Thanks!










951 Tarett Sway bar

T&T Racing

What is the blue color on the support bracket, over heated???

Porvair

I noticed that bluing also. No idea why that would be exposed to heat as its not that close to the turbo. Could that occur if something was binding and the metal fatigued? Seems really bizarre.

Just glad it happened on the street and not mid-turn on the track...

JustinL

It is REALLY easy to install the tarett bar in a way that it will bind. When you install it, put the bar in by itself without the end attachments. Torque up the hangers and then make sure the bar still turns freely before assembling the ends and attaching it to the control arm. If you torque up the hangers and it locks up the bar, then keep realigning them until the bar can turn easily and slide back and forth with all the hanger bolts tightened. I have the massive Tarett blocks for mounting the sway bar, but my tub wouldn't allow for me to get them torqued without binding the bar. PM me if you are interested in them.

RoyaleWithCheese

I can't remember where I read it, but on a forum post someone was saying that when using larger sway bars in racing applications the factory mounts are not up to the task. He was either using the Tarett braces or had fabbed something himself to support the factory mount and actually had cracking in the metal where the factory mount met the structure of the car (which iirc is the main frame structure).

I obviously can't verify that so take it with a grain of salt but I think there are far more forces being exerted on those flimsy mounts than they were ever intended to handle, at least in racing applications. Fabbing a stiffer mount would be a good start but if what happened to that guy is true then it sounds like those loads are just going to get transferred to the next weakest point which could be the sheet metal structure of the car.

MAGK944

T&T Racing

The photograph confirms that the mounts are Tarett supplied with the sway bar

Porvair

Justin L, It may have been binding but I guess that horse has left the barn so hard to confirm. I did confirm that the other side is seriously tweaked as well and it is canted forward which would not happen unless I ran over something backward (highly unlikely). I did jack up the drivers side of the car a week ago to check something on the exhaust and am wondering if that could have led to binding as it does put a fair bit of stress on one side vs the other and much less give at all pressure points vs stock..
That would be rather disappointing if that were the case. I will PM you on the mounting blocks.

Royale - I could definitely see the factory mounts stressing with a bigger bar. I did not have the Tarett configured to max stiffness so I would have thought that their mounting setup was more than adequate for the bar.

Waiting to hear from Tarett to see if they have seen this.

Thanks all!

RoyaleWithCheese

Oh I wasn't referring to the OP in my comment, I was talking about a different guy that had his frame crack from sway bar stresses.

I tracked down the thread that I was referring to here:
https://rennlist.com/forums/944-turb...his-d-lol.html

It seems that the factory mount/mounting location cracking and breaking is a common occurrence on 944s that are tracked hard or have too soft of springs for the stiffness of the aftermarket sway bar.

JustinL

I don't think you can make a fair assessment of the other side, because once the one mount broke, that bar would have been all over the place and almost certainly would have bound up the other side. I would still put money that the bar has been bound up since installation and was using the mount as a spring instead of torsion in the bar. Eventually it was going to go. If you aren't paying attention to this when you install it, it's so easy to just bolt it together and not notice that it's all locked up. I did this many times when I was trying to install mine before making custom mounts with careful consideration to the holes to make sure that all was aligned. Keep in mind it's a 3-D problem so the mounts can be trying to bend the bar in 2 planes it's not supposed to (up-down, front back). This was never a problem with those huge squishy rubber bushings, but the aluminum Tarett bushing housings leave almost zero room for misalignment.

It's kind of like the balance shaft covers that are align honed and if they aren't aligned, it locks up the balance shaft. This is just a problem over a longer distance between the holes.

T&T Racing

Is the Delrin bushing installed in the mounting block? What is the clearance between the mounting block and the shaft collar?

Porvair

I heard from the folks at Tarett and they suspect a binding issue as others have suggested. Sounded like this was not the first case. I am wondering if something got misaligned somehow as I did two track days following the initial installation of the bar and I did not notice any funky handling that would follow a binding suspension (like the snap oversteer I had on a Fox-body Mustang many years ago, where the rear suspension was notorious for binding).

And very good news on the customer service front; the good folks at Tarett are sending me new brackets (stronger design) gratis. Probably a small cost for them but I really do appreciate good customer service so I will be looking at their catalog next time I need more goodies.

Thanks for all of the comments as I will be most careful to ensure no binding. I did not fully disassemble the bar following this incident so am not sure of the clearances but make sure they are adequate.

JustinL

Good to hear. Keep us updated with the reinstallation.

ddombrowski

It cracked right at the highest stress concentration in the hole for a vertical load. Binding may have contributed to make the problem worse, but it still looks like a tensile failure in the direction of long dimension of the mount.

T&T Racing

The 944 Tarett sway bar system has a short drop link. If the sway bar is set for more than half soft to full soft or the splined arm attached to the tube is not installed properly, these combinations produce both a horizontal and vertical force on the bracket with force resultant trying to push the vertical support bracket forward. This puts the bracket in a shear mode.