Printable Version of Topic

Posted by: Matt Romanowski Jul 18 2017, 06:42 PM

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.

Posted by: Porschef Jul 18 2017, 06:53 PM

Dahaaamn! Must be a beast.

I believe Mr. Foley has what you need.

Thanks for sharing

What's that welded carabiner looking thingy?

Posted by: PanelBilly Jul 18 2017, 06:57 PM

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

Posted by: trojanhorsepower Jul 18 2017, 06:59 PM

ooh can I guess?

Tie down?

Posted by: burton73 Jul 18 2017, 06:59 PM

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

Posted by: Krieger Jul 18 2017, 07:01 PM

Holy crap!

Posted by: banananose914 Jul 18 2017, 07:06 PM

That is definitely an eyebrow raiser!

Posted by: Cracker Jul 18 2017, 07:16 PM

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

Posted by: Garland Jul 18 2017, 07:20 PM

Is that ring used for a tie down?

Posted by: Racer Jul 18 2017, 07:22 PM

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!

Posted by: Bartlett 914 Jul 18 2017, 08:00 PM

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

Posted by: rgalla9146 Jul 18 2017, 08:08 PM

What is the rating of those springs ?

Posted by: Matt Romanowski Jul 18 2017, 08:12 PM

375 lb.

Posted by: porschetub Jul 18 2017, 08:15 PM

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

Posted by: Matt Romanowski Jul 18 2017, 08:18 PM

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.

Posted by: Matt Romanowski Jul 18 2017, 08:19 PM

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.

Posted by: Cracker Jul 18 2017, 08:33 PM

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

Posted by: Matt Romanowski Jul 18 2017, 08:49 PM

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.

Posted by: Cracker Jul 18 2017, 09:00 PM

Thanks. Beautiful car Matt.

T

Posted by: Mark Henry Jul 18 2017, 09:19 PM

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.

Posted by: pete000 Jul 18 2017, 10:39 PM

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

Posted by: brant Jul 18 2017, 11:09 PM

Wow
Glad you are ok

Posted by: Racer Chris Jul 19 2017, 04:51 AM

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.

Posted by: Cracker Jul 19 2017, 05:34 AM

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

Posted by: McMark Jul 19 2017, 06:19 AM

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

Posted by: jd74914 Jul 19 2017, 06:28 AM

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?

Posted by: bdstone914 Jul 19 2017, 06:36 AM

Have you inspected the other arm for stress cracks ?

Posted by: Racer Chris Jul 19 2017, 06:37 AM

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.

Posted by: Racer Chris Jul 19 2017, 06:42 AM

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.

Posted by: McMark Jul 19 2017, 06:47 AM

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

Posted by: Matt Romanowski Jul 19 2017, 08:59 AM

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.

Posted by: Cracker Jul 19 2017, 09:08 AM

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

Posted by: jd74914 Jul 19 2017, 09:57 AM

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.

Posted by: gms Jul 19 2017, 10:35 AM

glad you caught this before something bad happened on the track

Posted by: Matt Romanowski Jul 19 2017, 10:50 AM

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

Posted by: stownsen914 Jul 20 2017, 05:24 AM

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

Posted by: GregAmy Jul 20 2017, 06:11 AM

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)?

Posted by: jmitro Jul 20 2017, 09:16 AM

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

PM sent

Posted by: Matt Romanowski Jul 20 2017, 12:25 PM

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.

Posted by: Matt Romanowski Jul 20 2017, 12:33 PM

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





I thought people miight like my co-driver's original, single owner Six.

Posted by: Rand Jul 20 2017, 03:03 PM

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?

Posted by: plays with cars Jul 20 2017, 03:16 PM

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.

Posted by: Dave_Darling Jul 21 2017, 09:54 AM

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



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

--DD

Posted by: JRust Jul 21 2017, 10:36 AM

Absolutely stunning six

Posted by: crash914 Jul 21 2017, 11:08 AM

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

Posted by: Spoke Jul 21 2017, 11:26 AM

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


Attached image(s)

Posted by: jmitro Jul 21 2017, 01:02 PM

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.

http://s75.photobucket.com/user/jmitro2000/media/2016-08-18%2007.57.30_zpsfussr0rc.jpg.html

Posted by: Matt Romanowski Jul 21 2017, 06:46 PM

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.

Posted by: ejm Jul 22 2017, 03:20 PM

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.

Posted by: Matt Romanowski Jul 22 2017, 07:19 PM

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!