I have a 70's bike with Shimano 600 arabesque components and just bought a pair of Shimano PD-M324. The threads on the new pedals seem to be just a tiny bit too big for the crank arm. I find this weird since (based on some quick research on Google and YouTube) there seems to be just one size for all pedal and crank arm threads, except for small kids bikes.

I'm wondering if anybody else has successfully mounted these pedals on a similar crank arm? Could the pedals be defective?

I can still put the old pedals back on so I don't think the threads on the crank arm are damaged. Any advice would be great!

  • If I recall correctly there were a couple of rare odd ball pedal thread sizes back in 'the early days' - not sure enough to make this an answer though. – mattnz Sep 19 at 9:33
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    Take the right pedal of each pair and lay the two threads alongside each other. The points of one should sit in the valleys of the other pretty well. You can compare the two pedals of each set and they should mesh like this right too. – Criggie Sep 19 at 10:03
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    @mattnz the only one I remember was dynadrive which was a 1" pedal thread, so massively and obviously different. – Criggie Sep 19 at 10:05
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    @jooooooooohn Silly thought - you do have the left and right pedals the correct way around? They appear to have L and R stamped into the wrench flats. – Criggie Sep 19 at 10:06
  • Yes, PLEASE make sure you're threading the right pedal into the right crank and the left into the left. Many a crank and pedal is ruined by getting them crossed. – Daniel R Hicks Sep 19 at 11:11
up vote 10 down vote accepted

You have the version of those cranks that came with French pedal threads (M14x1.25).

I believe there's enough material to tap them to standard 9/16x20. The difference in diameter is very slight. It's important and not trivial to get the tap going in square.

  • Cool good thinking - That's why I was suggesting to compare the two pedal threads. Would they be obviously different to the eye? – Criggie Sep 19 at 10:11
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    Debatable. French is 14mm and standard is 9/16", which converts to 14.2875mm. It's enough to be subtly noticeable when you're used to dealing with standard pedals all the time. That the pedals in question will be old and usually a French brand is a big clue. – Nathan Knutson Sep 19 at 10:17
  • Well, that makes sense. I didn't realise that's why it reads 14L and 14R on the old pedals (facepalm). At least now I know for sure that they should not fit. Thank you! – Jooooooooohn Sep 19 at 11:46
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    Note that this is only possible because the thread pitch is almost identical at 1.25mm vs. 1/20" (1.27mm). Ordinarily cutting a marginally bigger thread would be a bad idea as the pitch difference would mean a lot of material removed that's needed to support the thread. In that case (and potentially here) a helicoil could be used instead. See velo-orange.blogspot.com/2006/11/re-tapping-pedal-threads.html for more info – Chris H Sep 19 at 13:39
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    Finding French thread pedals might be rather tricky, putting in helicoils especially reverse thread helicoils rather expensive, maybe even prohibitive the only viable option might be to find suitable cranks. Which might also be more sensible in case of further replacements. You could possibly find a buyer for your French threaded cranks at a vintage bike parts market. – Carel Sep 19 at 17:40

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