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Advice wanted for a speedometer cable not fitting
(lemmy.world)
At risk of sounding a bit blunt, why not just look on eBay or any classic car parts websites?
If you don't trust them for whatever reason then you could go to a local scrap yard that specialises in old stuff. I'm sure the part will likely be cross compatible to all the GM stuff of the era.
But if you really want to bodge it, Speedo cables tend to be square, just file down the sides of the thing until it fits (unless someone can explain why that won't work due to different ratios or something). Assuming that it's the cable itself that's too big and not the screw on bit.