Broken shock shaft, cracked shock mount - Vintage Mustang Forums
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post #1 of 6 (permalink) Old 09-12-2019, 12:55 PM Thread Starter
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Broken shock shaft, cracked shock mount

Hello everyone,
My 1970 Mustang coupe just started making a squeaking noise. When I went to investigate, I found two things:

The driver's side shock shaft had broken at the very top, so the shock was no longer connected to the car body. Now, the shock shaft is just rubbing on the side of its hole as the suspension compresses and decompresses, making that squeak I heard.

Also, I found a crack in the sheetmetal near the passenger's side shock mount (the passenger's side shock is NOT broken and is still attached to the body). You know how there's two layers of metal around the rear shock mounts, the lower layer that the shock attaches to, and the upper layer that makes the trunk floor? The crack is in the upper layer. The lower layer seems alright as far as I can tell, though I have not yet had time to thoroughly inspect it.

Are these problems likely connected? What could have caused this? I do often keep a heavy toolbox and fire extinguisher in my trunk near the passenger's side shock mount, I wonder those things banging around may have caused the crack. How structural is that upper layer of steel? I'd have thought that the lower layer (the one that the shock actually attaches to) would be responsible for most of those forces?

Could the broken shock shaft have been caused by overtightened shock nuts? I didn't go crazy tightening them but I didn't use a torque wrench either.
Attached Images
File Type: jpg Broken-off shock shaft end.jpg (285.6 KB, 6 views)
File Type: jpg Cracked shock mount.jpg (486.1 KB, 4 views)
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post #2 of 6 (permalink) Old 09-12-2019, 01:19 PM
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Could be from that worn insulator over time gave up (hardening) dampening the shaft at the top.. Could be stress (fatigue) crack in the shaft? How old are your shocks? Could be time replace all shocks?

In the meantime, check the entire area for cracks in the towers, the lower frame, etc. Gotta remember how old these bodies are at this point.

Have you been adding to the stress with aggressive driving?

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post #3 of 6 (permalink) Old 09-12-2019, 01:25 PM
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Looks like its just the grommet hole thats cracked. Is the hole the shock actually mounts to cracked as well?
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post #4 of 6 (permalink) Old 09-12-2019, 01:26 PM
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A PO may have had air shocks on it at one time. A very common and well known way to destroy the upper mount.
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post #5 of 6 (permalink) Old 09-12-2019, 01:50 PM Thread Starter
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AS FAR AS I CAN TELL the actual shock mount isn't cracked, just the grommet hole. Of course I will inspect the whole area very thoroughly.

I most definitely have been adding to the stress with aggressive driving. I like to drive "spiritedly," and I have UHP summer tires.

The shock that broke is a Bilstein, so not cheap junk- though perhaps there was a flaw in this one? It lasted about a year and a half, or roughly 19,000 miles.

Tonight I will take the other shock off, carefully inspect everything, and, unless I find more damage, drill and weld the crack and install a pair of Monroe shocks.
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post #6 of 6 (permalink) Old 09-12-2019, 03:13 PM
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Over-tightening the shocks could do it I suppose, the bushings can be squished out, making the joint almost solid. That could cause the shock shaft to flex, probably breaking at the end of the threaded portion. You just want a decent bulge in the rubber bushings,

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