 I broke a rear trailing arm at the track!, Holy Cow! |
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| Rand |
 Jul 20 2017, 03:03 PM
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#41
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Cross Member  Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None  |
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?
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| PlaysWithCars |
Jul 20 2017, 03:16 PM
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#42
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Senior Member Group: Members Posts: 523 Joined: 9-November 03 From: Southeast of Seattle Member No.: 1,323 Region Association: Pacific Northwest 
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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. |
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| Dave_Darling |
Jul 21 2017, 09:54 AM
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#43
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914 Idiot Group: Members Posts: 14,981 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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Man, that Six!! Drooooooooollllllll......
I trust you are examining the suspension on the other three corners of the car very carefully? --DD |
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| JRust |
Jul 21 2017, 10:36 AM
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#44
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914 Guru Group: Members Posts: 6,305 Joined: 10-January 03 From: Corvallis Oregon Member No.: 129 Region Association: Pacific Northwest
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QUOTE(Matt Romanowski @ Jul 20 2017, 11:33 AM)  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. Absolutely stunning six (IMG:style_emoticons/default/drooley.gif) |
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| crash914 |
Jul 21 2017, 11:08 AM
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#45
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its a mystery to me Group: Members Posts: 1,826 Joined: 17-March 03 From: Marriottsville, MD Member No.: 434 Region Association: MidAtlantic Region |
I am going to with hydrogen embrittlement of the welds. Yep, that's it. Glad you and car are ok.
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| Spoke |
Jul 21 2017, 11:26 AM
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#46
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Jerry Group: Members Posts: 6,976 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None
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QUOTE(Matt Romanowski @ Jul 20 2017, 02:33 PM) Here are some more photos now that the arm is off the car. Is the dirt on the crack from cleaning after the tear or has is been torn for a while? Attached image(s) 
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| jmitro |
Jul 21 2017, 01:02 PM
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#47
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Senior Member Group: Members Posts: 713 Joined: 23-July 15 From: Oklahoma Member No.: 18,986 Region Association: None
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QUOTE(Rand @ Jul 20 2017, 04:03 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? 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. (IMG:http://www.914world.com/bbs2/uploads_offsite/i75.photobucket.com-18986-1471525938.3.jpg) |
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| Matt Romanowski |
Jul 21 2017, 06:46 PM
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#48
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Senior Member Group: Members Posts: 878 Joined: 4-January 04 From: Manchester, NH Member No.: 1,507 |
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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| ejm |
Jul 22 2017, 03:20 PM
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#49
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I can see the light at the end of the tunnel Group: Members Posts: 2,689 Joined: 3-February 03 From: Massachusetts Member No.: 224 Region Association: None |
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.
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| Matt Romanowski |
Jul 22 2017, 07:19 PM
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#50
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Senior Member Group: Members Posts: 878 Joined: 4-January 04 From: Manchester, NH Member No.: 1,507 |
QUOTE(ejm @ Jul 22 2017, 01:20 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. 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! |
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