I was at Mont Tremblant this weekend with my track car. It's got a stock 3 liter, 915 with Martin's shift conversion, great suspension setup. Weights around 2000 lbs. I came in from a run and the right rear tire had WAY too much camber. It was obvious it was broken and about to rain, so we loaded up and waited for the complete diagnosis for when we got home. Put it on the lift to find the rear control arm coming apart. I'll post up more photos and analysis when I get the arm off, but wanted to share these.

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Dahaaamn! Must be a beast.

I believe Mr. Foley has what you need.

Thanks for sharing

What's that welded carabiner looking thingy?

Would that be the result of driving all out. I'd say you were pushing it to the limit.

ooh can I guess?

Tie down?

I have never seen that. The good news is your OK because it could have been bad.

What it that you have welded to the bottom that looks like a locking oval some people use for key chains or backpacking.

Bob B

Holy crap!

That is definitely an eyebrow raiser!

Are your arms reinforced - I couldn't tell from the pictures. If they are, which ones or method (so we don't use them!)? Thankful it didn't cause a crash...

It really is not surprising given the fact the components on our cars are so old - really curious to know if improvements had been made...

Tony

Is that ring used for a tie down?

Usually they tear at the other end. Guess those sticky hoosiers are putting a lot of force through there. Does beg the question on your re-inforcement choice or how you will reinforce moving forward.

Glad it didn't end with a hit on a wall. Tremblant is such a fun track!

Wow that is incredible.. I think it has been cracked along the top for awhile. The break is not as clean looking

What is the rating of those springs ?

375 lb.

To much glue on the road and rock hard suspension......

The rings are for tie downs. I'm too cheap to buy something special, so I welded those on and the straps grab them.

I haven't run Hoosiers on this car in a long time. Our normal tire is the Nitto NTO1. We just bolted on a set of Hancooks.

The arms were not reinforced. The previous owner, about 11 years ago, had bought these refinished arms (powdercoated, bushings, new bearings). We changed them to Chris' delrin bushings a few years ago (they are way better than the rubber ones).

I've already been in touch with Chris. The car will end up with a set of his arms.

Or 41+ year old parts? I have full data in the car (oil temp, pressure, driver inputs, brake temps, tire temps, and shock travel). The suspension moves plenty. If it was any softer it would bottom out.

Matt - Again, very glad it cause an off...do you have a cage? Will you share any pictures
of the car? Chris will get you going and safe the next time you hit the track!

Tony

It's a full race car. Cage tied to the suspension mounts, NASCAR bars, etc. We have a Kirkey seat, 6 point harnesses, etc. It's a safe car and has all the goodies.

I don't have any photos of the cage, interior, or trunks, but this is the car at Tremblant a couple of years ago.

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Thanks. Beautiful car Matt.

T

Matt do you ever go to Mosport, now called Canadian Tire Motorsport park?

If you do drop in, I'm only about 5 miles off the highway on the way there.
I live about 25 minutes from Mosport.

I guess those reinforcement kits aren't just for looks after all !

Wow
Glad you are ok

I've never seen a failure like that on a trailing arm. Definitely a rarity.
I expected a tear where the front tube attaches to the box after talking with Matt on the phone quickly last night.
My reinforcing method wouldn't prevent that from happening.
I'm interested in seeing the component up close now.

Someone (maybe Matt) suggested a difference in the fractures - possibly showing different age. Could it have been cracked (lets say from the tie-downs) and then completing the deed on the track? Please let us know your thoughts Chris - I am very interested in your assessment!

PS: Matt: In which manner do you tie down in the rear - straps straight back or crossed? Also, do not clean the trailing arms prior to giving them to Chris...

Tony

That's a scary failure. Glad it all worked out...

That's crazy. Glad it didn't result in injury to you or the car.

Unrelated, but since you are a data guy have you seen the new multi-point tire temp sensors from IZZE Racing?

Have you inspected the other arm for stress cracks ?

Until I have a closer look I'm attributing the failure to high spring rate and curb hopping. Once a fatigue crack began at the top it didn't take long to propagate around the tube.

I see a change in the weld where the crack deviated. At that point the crack moved off it's HAZ path and took the shortest route toward the bottom.

Yeah, your post made me rethink what I was seeing. Now I see the failure obviously originated from the top side.

I have one of the sensors, along with analog versions from Texense and AiM.

For tie downs, we use the hooks on the arms straight (not crossed) to the trailer.

Chris brings up a great point in reference to the curbing. I have adopted a different approach to curbs this year...I stay off high-speed, significant (height) curbs! When the components and tubs are up to 47-years old like they are on our teeners - I felt a slightly slower lap time and different line was worth the tradeoff of protecting my car from that kind of abuse. Just sayin'...

T

Sorry for the hijack again but how do you like it? I've used the Texense sensor (seems to work well and Pierre is awesome) but its $$ and single point.

glad you caught this before something bad happened on the track

No worries. Shoot me an email at matt@trailbrake.net and we can discuss.

Jeez Matt, that sucks, but glad it didn't end worse for you!

And thanks for posting too. Good reminder that we need to be checking our 40+ year old cars for stuff like this.

Scott

I'll be checking my racer as well, but I have to wonder if the welding on that bit, along with getting jacked down pretty hard there regularly, contributed to the problem. Do you cross-strap and do you jack it down pretty hard to pull down the suspension (I don't do either)?

wow; glad you didn't have a major accident.

PM sent

We put the straps straight back. We don't go crazy pulling it down, so I don't think that was it. The other side doesn't show any signs of cracks or any problems. I'm thinking this might just be a fatigued 40something year old part. I'm heading down to see Chris tomorrow and we'll see what he thinks.

Here are some more photos now that the arm is off the car.

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I thought people miight like my co-driver's original, single owner Six.
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I see a lot of talk about reinforcing. But the reinforcing I've seen on trailing arms is farther down the arm, nowhere near the area where this one let go. Are there reinforcement kits for the area that failed here? Any links to them or what people have done with custom fab?

Wow! So close to this becoming a major event on the track. Glad you caught it before it did.

I suspect that the failure mode is 40yrs of fatigue. Every manufacturing process has variation and it could be that this was a 'weak' point in the original assembly that after 40yrs of use finally became a crack initiation site. Watching with interest to see what is determined after more inspection.

Man, that Six!! Drooooooooollllllll......



I trust you are examining the suspension on the other three corners of the car very carefully?

--DD

Absolutely stunning six

I am going to with hydrogen embrittlement of the welds. Yep, that's it. Glad you and car are ok.

Is the dirt on the crack from cleaning after the tear or has is been torn for a while?

Here's my arm, reinforced with Maddogs Motorsports kit. If welded correctly, in my opinion this kit would prevent the type of failure we see here.

After looking at the really broken arm with Chris and Ed today, I had some time to check the other arm. It was cracked right were Ed thought it thought it was started. I'll have to figure out how to remove the powder coat on these arms so we see how big the crack is and see what happened.

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Very interesting find. On your failed arm there's a 3/8" long place in that area that has been chafing and rusting for some time. I was thinking it was a random failure but maybe that's an unrecognized stress point when the arm is loaded in multiple directions.

On FB, Greg Fordahl said he's had 2 arms crack in the same place. He said he re-tig welded the entire arm and then heat treated the arms (while jigged). Makes me think about getting these done....

Thanks for the great find!