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Method of fixing damaged threads on rear shock lower mount

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Method of fixing damaged threads on rear shock lower mount

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Old 09-11-2018, 12:57 PM
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Method of fixing damaged threads on rear shock lower mount

I cross threaded a lower shock mount bolt. They are coarse M14x2 and go in at a slight angle which makes them super easy to cross thread especially when you're trying to get everything lined up. Even with clean threads and hand tools I managed to bung up the first thread and a half in the nut that is part of the frame. From the backside there isn't enough room to get a tool, bolt, or wrench up in there.

I ended making a 'tool' from a grade 10.8 bolt to come in from the back of the threaded hole to un-frig the threads. Basically I cut the head off a bolt, machined an 8mm hex head, and ground a screwdriver slot. It could certainly be done with just a grinder or cutoff tool and a some patience.

Photo Attached.

The slot is so it could be started with a screwdriver until the hex head protruded enough to accept a socket. Lots of oil was used to prevent galling during thread correction and to reduce torque so the little hex head wouldn't break off. It went through very well and didn't require any concerning amounts of force..

Now I realize that the damaged threads aren't 'fixed' but rather just re-aligned to not interfere. I decided that the remaining good threads were suitable for the job to get me back on the road. This is an assessment that anyone else will have to make given their situation and safety so do it at your own risk.

I saw that someone else fixed one of these by drilling it out and using a thread repair/insert kit. That's probably a better method if you can find one quick enough. The stores around here only had them up to M12 size.

Just sharing in case this can help someone out of a pickle.

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Old 09-11-2018, 01:31 PM
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Could you have used a cut down M14x2 tap ? Or a thread chaser ?
Nice you have the machine skills to put a hex on the cut off bolt.
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Old 09-11-2018, 01:35 PM
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Good job, it got you back on the road. So, long as you could torque the bolt to specs, you’ll be fine.
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Old 09-11-2018, 02:56 PM
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Originally Posted by Cat Man HHR View Post
Could you have used a cut down M14x2 tap ? Or a thread chaser ?
Nice you have the machine skills to put a hex on the cut off bolt.
Yeah, I looked locally for a an M14x2 tap or thread chaser... nothing. But then again it was 7pm and I had to take my wifes car to town to find a solution that night knowing I would be stuck at home until fixed. Anyways it was the threads at the front of the hole that were messed up so there would be no way to 'catch' them other than starting from the back where the good ones were. My machine skills are extremely limited. I did the hex on an ancient manual mill in a crude fashion eyeballing it and continually testing with a socket then touching it up on a belt sander. It's not concentric or precise, just good enough to save my butt. I'm sure this could have been done with a grinder and a vise.

The majority of the threads were intact. It torqued fine, didn't baby it. Of course I'll be keeping an eye on it for a while but ultimately if I felt it was a sketchy fix I wouldn't run it.
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Old 09-11-2018, 04:32 PM
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Good, keep us informed.
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