Anybody know what this dimple is ?

More than likely, it was for a locator/clamp used when manufacturing the part. There may have been multiple suppliers and some used it, others didn't.

55Moredoor said:

In the process of rebuilding my control arms I noticed this dimple in the driver's side lower arm. It's the size of a hammer head but I doubt that any human could swing a hammer hard enough to leave a mark this deep in metal. I don't have the car here to see if anything on the driver's side needs clearance but I don't remember anything there. The passenger side doesn't have the dimple at all.
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Just wondering, when you reinstall the lower a arms are you going to be using stock springs?
if so, what will be your method of compressing the coil spring and attaching the lower a arm?
just wondering, I'm planning on doing this job too.
Thanks

Use a compressor spring, if you haven't got one there are places that hire them out, or you can make your own with threaded rod

I think Rick_L has instructions how to build your own spring compressor.

angs1957 said:

Use a compressor spring, if you haven't got one there are places that hire them out, or you can make your own with threaded rod

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I made my own spring compressor / lower A arm installation tool using a length of threaded rod purchased at either Lowes or Home Depot. I made the bottom bracket out of heavy gauge steel. I also employed a safety back-up just in case things "let go". I believe I used rope looped a few times through the spring and tethering to the A arm and frame.

Here's how Pop's did his.

Back to the dimple, Rick L, probably called it right being a locator spot for a clamp, could it also have been to add a little structural integrity to that section of the arm?

Beachcomber said:

could it also have been to add a little structural integrity to that section of the arm?

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The flanges provide most of the structural integrity. The dimple is in a meaningless area for that.

I agree with Rick, if it were something for structural integrity you would think them all would have it. The other side of the car doesn't.

+1 on the spring compressor tool from Pops thread. I made one and it worked great!

Mister56 said:

Just wondering, when you reinstall the lower a arms are you going to be using stock springs?
if so, what will be your method of compressing the coil spring and attaching the lower a arm?
just wondering, I'm planning on doing this job too.
Thanks

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As was posted several times above, I was lucky enough to have a friend who owns a spring compressor which I used and it made the job easy.

My lower arms have the dimple. I call it the little dirt collectors lol. I don't know what they were/are for.
Todd

Dimple was put there for the mounting of the front stabilizer bar. Early ones even had a hole in it. I believe this was the plan, and the
maker of the control arm made them that way. By the time the cars were getting made there was a change to the way the mounting
was made, by then the tooling was done, and there was no reason to remove it.

55wagoncrazy said:

Dimple was put there for the mounting of the front stabilizer bar. Early ones even had a hole in it. I believe this was the plan, and the
maker of the control arm made them that way. By the time the cars were getting made there was a change to the way the mounting
was made, by then the tooling was done, and there was no reason to remove it.

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Do you think that since mine has one with and one without the dimple that the lower control arms were swapped at one time? The ball joints were still riveted into the uppers so I think those were originals.

The design of the lower ball joint was very good. However mechanics were taught to lift the suspension with a jack to check for ball joint
play. The lowers would come out of their seat when this was done. The ball seated properly when the coil spring was in place.
It was the way they were designed. So stupid mechanics would replace good GM ones with inferior ones and charge for it.

This is about 98% of the reason lower ball joints are replaced even on very low mileage 55-57 cars

Not 100% of the lower control arms had the dimple. There were many suppliers for the frames and parts used to build them.