Has anyone broke one of these yet? (Rear Lower Control Arm Endlink Tab)

[Dynabyte]

Pete - responses to your questions have been emailed. Thanks much for your diligence!

[Darth_Emma]

I watched Pete's video. Didn't PQ's second control arm fail AFTER he put the bigger washers on? Maybe it was already on its way to failing, but I thought he had done the fix Pete is recommending based on their preliminary findings.

[JusticePete]

Originally Posted by Darth_Emma

I watched Pete's video. Didn't PQ's second control arm fail AFTER he put the bigger washers on? Maybe it was already on its way to failing, but I thought he had done the fix Pete is recommending based on their preliminary findings.

Use the force and you will find that PQ installed his new endlink on the old arm and it wasn't looking as good as new.



You can see how the endlink tab material appears deformed and consistent with the failure of the other arm. Pictures can be deceiving. The arm in question is in transit. My guess is it will arrive while I am at the Fest so it will be next week before I see it. If it arrives in the morning, I'll get pictures up before I fly out.

This is the fix I am talking about. The idea is to keep the upper portion of the tab from flexing across the arm as opposed to up and down.



Disclaimer -- We have not completed our research. We are reaching out to Pedders, GM and any other dealers or owners that have knowledge of RLCA failures. We have complete details on one and counting. What is common in the failures?

1. Both were lowered
2. Both had large diameter rear bars

What is different?

One is a six and one an 8

As we get more information, we will post it here.

[Darth_Emma]

I've been following this discussion pretty closely, so, yeah, I saw that PQ had been using that control arm for quite some time before using the larger washers.

My car and PQ's car are very similar builds, so I'll continue looking for updates. My car was on a lift today, so I had an opportunity to get a good look at the control arms and they seem to look fine, at least for now.

Thanks for keeping us posted on your findings.

[JusticePete]

Originally Posted by Darth_Emma

I've been following this discussion pretty closely, so, yeah, I saw that PQ had been using that control arm for quite some time before using the larger washers.

My car and PQ's car are very similar builds, so I'll continue looking for updates. My car was on a lift today, so I had an opportunity to get a good look at the control arms and they seem to look fine, at least for now.

Thanks for keeping us posted on your findings.

What you found, nothing unusual, is what we think most will find. We'll miss you at the Fest.

[LightningSS]

I talked to a colleague, an ole gray-haired stress analyst, much older and wiser than I. We work on airplanes, but he is also an old school gearhead. He suggested looking into the vertical travel of the wheels.


As you know the wheels can move independantly in opposite directions, and the purpose of the sway bar is to dampen this motion. Suppose the sway bar isn't there. Let's say each wheel can move up or down 3 inches until they hit the "stops" whatever that may be. So if the sway bar dampens that, ie, it keeps the difference between the two tires to something less than 6 inches releative to each other.


Say the max difference is 6 inches, meaning if anything forces the tires further apart the design load of the structure is exceeded and something has to give (PQ's bracket). And it probably takes a heck of a lot to exceed this.



So the OEM sway bar is designed to allow the 6 inch differential and keep on tickin'. The 6 inches is determined by the designers as the max travel the wheels will ever see in their lifetime plus some margin of safety probably.


Now you change out the OEM sway bar for a stiffer one. It is only going to allow 4 inches of differential until you hit the same design load in the structure. But, the wheels may still see the 6 inch differential in real life. What happens?

OEM bracket breaks.

[PQ]

Originally Posted by Darth_Emma

I watched Pete's video. Didn't PQ's second control arm fail AFTER he put the bigger washers on? Maybe it was already on its way to failing, but I thought he had done the fix Pete is recommending based on their preliminary findings.

In fact the second arm was failing already. I put those washers on it so I could drive it while the dealer was getting me one. I noticed the bending of the tab so I took it apart to document it and get pics. Then put the temporary washers on.

Pete, I'll answer all of those questions tomorrow evening when me and Chris get to Phoenix and I got some time to relax. Right now it's sleepy time. We just put 19 hours behind us.

Oh, and in all the bustle getting the oil and wheels done I didn't mail the other LCA so I brought it with me.

[JusticePete]

Originally Posted by LightningSS

I talked to a colleague, an ole gray-haired stress analyst, much older and wiser than I. We work on airplanes, but he is also an old school gearhead. He suggested looking into the vertical travel of the wheels.


As you know the wheels can move independently in opposite directions, and the purpose of the sway bar is to dampen this motion. Suppose the sway bar isn't there. Let's say each wheel can move up or down 3 inches until they hit the "stops" whatever that may be. So if the sway bar dampens that, ie, it keeps the difference between the two tires to something less than 6 inches relative to each other.


Say the max difference is 6 inches, meaning if anything forces the tires further apart the design load of the structure is exceeded and something has to give (PQ's bracket). And it probably takes a heck of a lot to exceed this.



So the OEM sway bar is designed to allow the 6 inch differential and keep on tickin'. The 6 inches is determined by the designers as the max travel the wheels will ever see in their lifetime plus some margin of safety probably.


Now you change out the OEM sway bar for a stiffer one. It is only going to allow 4 inches of differential until you hit the same design load in the structure. But, the wheels may still see the 6 inch differential in real life. What happens?

OEM bracket breaks.

Well said sir. Overload and fatigue are primary suspects as are a number of other factors.

1. Lowering coils
2. OE sub-frame bushes
3. Light coil rate
4. Light damping rate

These factors would add to and increased loading of the sway bars and the mounting tabs. Earlier in the thread one post mentioned flexing of metal or wire and the resulting failure which is very similar to your post.

Other factors could include but are not limited too:

1. Violent Wheel Hop
2. Side Load Impact damage
3. Improper Installation
4. Design Limitations

We will work through the data we collect from this thread along with the data we collect outside the thread. We will have a definitive response as the end result.

[NetPhilosopher]

My opinion is that the primary causal factor is the larger stabilizer bar.
The tab on the stock RLCA isn't designed to handle a much larger bar than the stock rear FE3 stabilizer bar. This stress will also get worse if you open the hole larger (less material on the tab) to accept a larger stud for a heavy duty balljoint link.

Regarding lost nuts: an undertorqued joint only needs to slip once. Even loctite will probably not help you, once a shear joint has lost clampload integrity, it's a matter of minutes before the nut backs off.

Hypothetically, if you are going to upsize the stabilizer bar, then you should proabaly also reinforce the tab/bracket on the RLCA. If it breaks in the future, warranty on this part will probably be denied, of course, as this is not a recommended modification to your vehicle. A better choice would be to move the pickup points outboard of the spring/shock and use a different type of stab bar attachment. This would allow a much lighter and more efficient rear stabilizer bar.

JMHO.

Of course, YMMV.

[JusticePete]

Originally Posted by NetPhilosopher

My opinion is that the primary causal factor is the larger stabilizer bar.
The tab on the stock RLCA isn't designed to handle a much larger bar than the stock rear FE3 stabilizer bar. This stress will also get worse if you open the hole larger (less material on the tab) to accept a larger stud for a heavy duty balljoint link.

Regarding lost nuts: an undertorqued joint only needs to slip once. Even loctite will probably not help you, once a shear joint has lost clampload integrity, it's a matter of minutes before the nut backs off.

Hypothetically, if you are going to upsize the stabilizer bar, then you should proabaly also reinforce the tab/bracket on the RLCA. If it breaks in the future, warranty on this part will probably be denied, of course, as this is not a recommended modification to your vehicle. A better choice would be to move the pickup points outboard of the spring/shock and use a different type of stab bar attachment. This would allow a much lighter and more efficient rear stabilizer bar.

JMHO.

Of course, YMMV.

Good post and valid points. Relocating the sway bar is the best solution and will be part of the ZL1 suspension.

[JusticePete]

PQ provided a pre-failure arm. The second arm has been invaluable. It is in transit from the FEST. I'll post detailed pictures and additional information as soon as it arrives.

[TAG UR IT]

Guess what....

[Darth_Emma]

Originally Posted by TAG UR IT

Guess what....

Are you in PQ's special club?

[PQ]

Originally Posted by JusticePete

Good post and valid points. Relocating the sway bar is the best solution and will be part of the ZL1 suspension.

I wonder if the ZL1 LCAs can be used on the SSs?

Originally Posted by TAG UR IT

Guess what....

Sucks to hear. I can't believe it's taken this long to discover this on these cars.

Originally Posted by Darth_Emma

Are you in PQ's special club?

Yup. It appears so. First the fuse pull and now this. I guess I'm a jinx.