I don’t know if you are still looking for a solution but if you are you could try an adhesive mount instead with a tension ball to Garmin dash cam arm.

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i had a similar concern with mounting a Garmin47 on the rear hatch of my hatchback due to having to slam it closed.

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I use this kit: https://www.amazon.com/iSaddle-Adhesive-Sticky-Holder-Navigator/dp/B01B81CQQU

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here is another option that might work better with the vertical glass. Use the adhesive part instead of the suction cup.

https://www.amazon.com/Dosili-Suction-Garmin-010-12530-00-010-12530-05/dp/B07VXBKS7Z