Front Lower A Arm just snaped how does that happen?

[2000_Black_RT10]

For one, the car is held up by the a-arm. I can't imagine that causing harm by jacking the car that way. There should be tell-tale scars if so under the arm left by the jack.

125 at 1.6G??? That was my point...

The car is surely held up by the arms, but the arm encounters tension and compression along the arm centerline.. it's not designed to support the vehicle with a load perpendicular / vertical to the arm (i.e. putting a jack under the arm). I know you know better than to do that..

The arm also supports a bending moment & twist in dynamic situations, but in the opposite direction of a jacking direction, the cross section is like a rotated I-beam, whereas if you put a jack under the arm it's like flipping an I-beam on it's weaker side..

 

[Martin2000GTS]

Jeeze you guys are more into my problem than I am haha. I should be getting the part in the mail tomorrow and I wil be installing it with my dad. I will take pictures of the progress and post them, ill also take more pictures of the bushing and control arms to see if we can pinpoint the reason the part failed. Just to answer a few questions, the only thing differnt from stock suspension wise is the eibach lowering springs, I have 19in HRE wheels with a 285 wdith tire on it. Hmm what else.... o ya...the front tires dont show any uneven wear. However the rear tires are worn very unevenly ill take pictures of that as well.
Thanks for all your help, this website is awesome!
Martin

 

[Martin2000GTS]

haha i was kinda lucky that it broke right infront of my drive way......to bad I cant get it in my garage, the car has been sitting on the side of the road since last Friday......uhhh i hate that, at least I got a car cover on it

 

[2000_Black_RT10]

Jeeze you guys are more into my problem than I am haha.

See what happens when we start at it.. ok, I was bored being home & sick today.. killed some time playing around..

See the GIF for animate stress on the control arm below, I quickly modeled something similar to your pics, and toss in some forces and a twist, cast aluminum material..

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Stress GIF:
[media]http://www.wincom.net/mnllehti/Control_Arm_GIF_08_28_2008.gif[/media]

To pursue Tom's suspicion of internal pressure of the pressed in collar, if I toss in some pressure on the inside surface, you can see where the stress peaks (the red region) in the pic below, as I feel if there was an oversized bushing sleeve, first place it should crack is on the inboard side, the optimum place for strain to occur, furthest from the arm material, and in the center where the shear plan is the least (inside of the external ribs). Yet! If there was a stress riser, a crack or material / casting defect, the crack would propogate from that region.. but I still find it hard to believe that that pressed in collar, a mild tube sleeve could crack that aluminum casting witha machined surface, especially due to the reinforcement ribs that wrap around the diameter.

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If you ever wanted to mail me that broken arm, I could identify how it cracked at work.. maybe the next time we visit our inlaws in Mass I could pick it up...

PS - Mak - if you catch this, please oh please don't make fun of my GIF.. (sarcasm alert!). Just kidding!

 

[Makara]

See what happens when we start at it.. ok, I was bored being home & sick today.. killed some time playing around..

See the GIF for animate stress on the control arm below, I quickly modeled something similar to your pics, and toss in some forces and a twist, cast aluminum material..

You must be registered for see images

Stress GIF:
[media]http://www.wincom.net/mnllehti/Control_Arm_GIF_08_28_2008.gif[/media]
To pursue Tom's suspicion of internal pressure of the pressed in collar, if I toss in some pressure on the inside surface, you can see where the stress peaks (the red region) in the pic below, as I feel if there was an oversized bushing sleeve, first place it should crack is on the inboard side, the optimum place for strain to occur, furthest from the arm material, and in the center where the shear plan is the least (inside of the external ribs). Yet! If there was a stress riser, a crack or material / casting defect, the crack would propogate from that region.. but I still find it hard to believe that that pressed in collar, a mild tube sleeve could crack that aluminum casting witha machined surface, especially due to the reinforcement ribs that wrap around the diameter.

You must be registered for see images

If you ever wanted to mail me that broken arm, I could identify how it cracked at work.. maybe the next time we visit our inlaws in Mass I could pick it up...

PS - Mak - if you catch this, please oh please don't make fun of my GIF.. (sarcasm alert!). Just kidding!

You get props for running a stress simulation. The lighting in the first image though...

 

[2000_Black_RT10]

Mak - I've realized software is not just my limitation.. I need to buy a book or.. you're lucky and I envy your location in the West coast for several reasons.. including the automotive styling schools & studios.

Now that I'm up way past my bedtime, sleep schedule is waaay messed up.. but thanks to the "Dave & Tom" team for keeping me an active member and surely delighting all viewers with this stuff.. here's another one showing the stress concentrations if a jack were placed under the arm to lift the car, just showing that the arm shouldn't crack around the bushing..

Good night!
Mike

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Stress GIF:
[media]http://www.wincom.net/mnllehti/Control_Arm_Jack_GIF_08_28_2008.gif[/media]

 

[Fatboy 18]

Very impressed with all the detail and computer drawings on here
After recently seeing the post put up by Baz UK, I went round my car and checked and cleaned all control arms and other components. Thankfully everything was ok. Oh yea, my car too has had track time at Button Willow

 

[dave6666]

The car is surely held up by the arms, but the arm encounters tension and compression along the arm centerline.. it's not designed to support the vehicle with a load perpendicular / vertical to the arm (i.e. putting a jack under the arm). I know you know better than to do that..

Umm... Well...

No, actually if I want to remove my Race Ramps out of the way for work more extensive than say an oil change and such, I'll place a 2x6 right inboard of the ball joint with a bottle jack underneath to lift the car off the ramp. And then of course find a cozy spot for a less obtrusive jack stand.

End result is that I am jacking via the a-arm, but right at where the load transfers between the knuckle and the arm, and well distributed. I will not change that occasional habit after this thread.

Now if Bruto the tire shop monkey came along and put his or her service jack on a single arm like the stress you've suggested, I agree that would be bad. Maybe double bad. Bad enough that I would not do something that silly.

Finally, Bruto the tire shop monkey could be female. We should always be open minded of and respectful to these issues of women's rights. In either case though, Bruto has hair. Enough so to confuse us. Enough so to ensure Chad will never offer a photo op using his McBackdrop.

Sorry. Might have gotten carried away there...

 

[Tom F&L GoR]

Actually, Mike, can you ****** with your software and work backwards to create a stress that produces the fracture shown? I'd have to look again, but the UK broken arm was similar, wasn't it?

 

[Bolt]

Great stress analysis! Thank you

 

[2000_Black_RT10]

Actually, Mike, can you ****** with your software and work backwards to create a stress that produces the fracture shown? I'd have to look again, but the UK broken arm was similar, wasn't it?

I can play around in different axis of force directions to optimize the target stress peak at the crack location, I know what you are thinking Tom.. but any level of force simulating a suddenly stopped tire and the inertia of the vehicle, the result keeps ends up looking like this.. stressing near the location of the crack. The nature of fracturing aluminum is why I tended to think it was a harsh / quick impact of some sort.. This is just a quick model, it does not represent an accurate manufactured material, part representation or a validated dynamic simulation.. Can you imagine if the SRT folks were to see this, who is this guy.. ***??

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Dave - I know you know.. you're a smart bugger.. Thanks for the fun.. Bolt & Fatboy.

 

[Makara]

Mak - I've realized software is not just my limitation.. I need to buy a book or.. you're lucky and I envy your location in the West coast for several reasons.. including the automotive styling schools & studios.

Ah, you know I'm just messing with you...

CG lighting is not easy. Personally, I'm a much better lighter in a studio than on a computer. Just try some simple three point lighting and you will find some big improvements, if that is what you are after.

 

[GTS Dean]

but any level of force simulating a suddenly stopped tire and the inertia of the vehicle, the result keeps ends up looking like this.. stressing near the location of the crack. The nature of fracturing aluminum is why I tended to think it was a harsh / quick impact of some sort..

You must be registered for see images

It looks to me like a pure tension failure. Somebody probably curbed or potholed it with the wheel turned outward, adding more moment to the arm.

 

[2000_Black_RT10]

It looks to me like a pure tension failure. Somebody probably curbed or potholed it with the wheel turned outward, adding more moment to the arm.

btw Dean - I have read many replies from yourself in the past, and I just wanted to mention that you are typically spot on.. as well as sharing some excellent track experience, suspension tuning tips, etc.. is great stuff.

 

[dave6666]

It looks to me like a pure tension failure. Somebody probably curbed or potholed it with the wheel turned outward, adding more moment to the arm.

That's still scary stuff. I mean, I know that the typical sports car owner would cringe at the thought of such an event, probably in some cases of donating a child just to rewind such an event, but practicality says none of that applies. Stuff happens, and if that car is not designed to take a *** hole w/o catastrophic suspension failure?

C'mon now...

Everyone says how "tough" these cars are. I would beg to differ that at least there were some other contributing factors.

And the discussion rumbles on...

 

[Martin2000GTS]

Hey guys,
I got the part on Friday and installed it. It took a while because my dad and I dont have all the correct tools. Everything came off pretty easily except the big ball joint. Luckily after my neighbor watched us banging on it all night and not being able to get it off he came over the next morning and used a special wedge shapped tool and banged it right off. Put the whole thing together and the car drives fine now. Im assuming I need to get an alignment even though the car seems to drive perfect. When I (well I mean my dad) haha installed the new a arm i noticed how it moves back and forth which im assuming is part of the alignment adjustment. I took a bunch of pics from the install and a bunch of pics from the broken part, I will email them to mike and if he dosent mind posting them again then that would be great. Interesting job on the computer analysis on the broken a arm, i cant wait to show my dad that, he's gonna go nuts being a physisist <-- cant even spell his profession... he is really into that stuff. Ill mail the part out if you want to inspect it, Def dont mind doing that as we probably are all pretty interested in the reason for failure. I never hit the arm on anything at least I dont rememeber doing it, and i never let anyone else drive my car, so i really dont know the reason, anyways give me untill Tuesday to get to post the pics and if you wanna pm me your address ill send ont the a arm.
Thanks for all the help and interest
Martin

 

[dave6666]

Yes you need an alignment!

Probably need to torque all your fasteners too, if you didn't have a torque wrench.

 

[Martin2000GTS]

def. didnt have a torque wrench but i can get one, anyone know the specs on how tight everything should be?

Anyone reccomend a good alignment shop in the MA area?

Thanks
Again.

 

[GTS Dean]

I don't have my book handy, but the wishbone pivots torque to 75 lb-ft. You should really make the effort to properly ballast and retorque ALL your pivot bolts and shock bolts if you did not do so after the spring change. From experience, it makes a BIG difference in the rebound control of the car. Depending on how much you have driven since the springs were done, you might have torn or damaged bushings here and there.

00 black - thanks for the compliment. I've been driving and working on these cars for 15 years now and probably have over 7000 track miles under my belt. In my construction and materials business, I see some really impressive failures.

 

[Nadine UK GTS]

Do you know if the car was ever shipped and if so how it was tied down? I mention this as I've seen these type of failures in the UK some years ago on a couple of cars, the failure happened some months later...and we found out that the cars were transported by strapping them down through the A-arms (doh - not the wheel/tire).

 

[Martin2000GTS]

2000 RT 10,

send me your address and i will ship you the parts that broke out this week. id like an explanation of why it broke!!!!

Thanks
Martin

 

[Martin2000GTS]

Hey Nadine my car since I have had it has never been shipped or towed, its been problem free for the whole time I have had it. So prior to 2004 the car had 4k on it when i bought it from Heffner, but im sure he knows the correct way of moving a viper around with out hurting it. I dont see any divits or markings on the a arm (assuming I could possibly have hit something) Im still wondering why it broke but at least im up and driving again, car seems to drive perfect but im sure it needs an alignment. Hopefully I can get that done this week.
Martin

 

[GTS Dean]

Do you know if the car was ever shipped and if so how it was tied down? I mention this as I've seen these type of failures in the UK some years ago on a couple of cars, the failure happened some months later...and we found out that the cars were transported by strapping them down through the A-arms (doh - not the wheel/tire).

NOW we seem to be getting somewhere.

 

[Vic]

As someone here said, that looks like fore-aft stress. If you think about it, under braking, on the front wheels, both the upper and lower a-arm's forward attachment points want to pull away from the frame in tensile, tending to "stretch" the bolt hole open. The tire wants to stay where it is, while the brake rotor is clamped, but the car wants to keep going forward w/inertia. This tends to twist the a-arm backwards, pulling the fwd point away from the frame, pushing the rear point into the frame. The material around the bolt hole in the a-arm looks pretty thin there, but is probably ok, unless there is some damage as has been discussed.

The rear a-arms fwd+rear attachment points alternate between tensile and compression, during acceleration and decel.

Over bumps, I think all four top a-arms attachment points are in compression, and the bottoms are in tensile. Because of the springs pushing downward on the lower arms, the angle is not strictly in the horizontal axis, but still in tensile nonetheless. Hitting a bump under braking would put tremendous tensile stress on the front lower a-arms fwd attachment points, both from the force of decel, tending to twist the a-arm backwards, and the force of the bump, tending to pull the lower arm outward+downward from the frame. Thats two sources of tensile stress at the same time. Its a wonder how that thin aluminum around the bushing area survives.

geeze, sure is a lot of forces acting on those bushing hole areas, but failure is nearly unheard of. Must be a good high-grade aluminum alloy.

I'd like to see the outer surface of the a-arm through a microscope, might have evidence of corrosion.

 

[klamathpro]

Crap Man! Good that you got it fixed so fast, but dang! That's scary! I'm glad Gen1's don't have this problem, or I'd be checking that thing every night.

 

[99 R/T 10]

More pictures from Martins car and the completed job:

 

[Martin2000GTS]

thanks for posting the pics! thats the completed job it was tough replaceing it. I had a hard ttime seperating the ball joint part, luckily the mechanic across the street came over with a fork shapped tool that was also wedged shapped, to take off the a arm where the ball joint was. I guess after 8 years of being stuck together its really gonna stick! Now I need to get a camber alignment anyone know anygood shops in the MA area?

 

[GTS Dean]

More pictures from Martins car and the completed job:

[media]http://www.wincom.net/mnllehti/Control_Arm_Force_08_28_2008.jpg[/media]

Aren't computers amazing?

 

[dave6666]

It's interesting how the 2 pieces don't match up well on the right side of the close-up pic.

 

[Tom F&L GoR]

Save that black metal shock bracket. It can be mounted on the forward or rearward side to make the lower arm a left or right a-arm.