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Old 04-23-08, 05:04 AM   #1
zacster
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Pedal thread size?

Simple question. Are there different pedal thread sizes for the varying types and manufacturers of cranks? I have a pair of older SPD pedals that I couldn't get onto one of my old bikes with an even older Campy SR crank, early 1980s. It wouldn't thread all the way on. I put those same pedals on a different bike from the same era, with a Zeus crank, and it worked. But I've also swapped pedals between those bikes in the past without problem.

What I'm looking to do is put these pedals on my current ride, a Kuota CF bike with an FSA SLK crank, not as a permanent addition but to allow someone to give it a test ride. She rides her current bike with SPDs on it. This way we can swap bikes back and forth without having to swap pedals on the road. (She's also drop-dead gorgeous and could beat the pants off me in our indoor cycling class and about 20 years younger.) I don't want to start threading them in only to find myself ruining the soft crank thread.

I just hope my shoes with the SPD cleats haven't fallen apart. They look to be in better shape than my current road shoes, but you never know if some glue has given up after all the years.
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Old 04-23-08, 11:28 AM   #2
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I know that the threads on the crankarms are usually pretty soft, and I've never swapped on my current bike. Over time though I've swapped around on my old bikes enough. I'll give it a try, and make sure the threads are lubed.
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Old 04-23-08, 10:03 PM   #3
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The threads are both 9/16" x 20tpi, but the thread shape is a little different. I have a set of Shimano pedals in a pair of Campy Nuovo Record cranks- the fit is very tight. I have to wrench them all the way in where other cranks accept the same pedals with finger pressure. Remember to grease the threads!

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Old 04-24-08, 02:08 AM   #4
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Could you possibly have "old French" cranks with 14mm x 1.25 pedal threads, which according to Sheldon can be tapped to 9/16 inch? But where are you going to get a left hand tap?
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Old 04-24-08, 06:18 AM   #5
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Could you possibly have "old French" cranks with 14mm x 1.25 pedal threads, which according to Sheldon can be tapped to 9/16 inch? But where are you going to get a left hand tap?
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Old 04-24-08, 08:21 AM   #6
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Woo Hoo

I'm working on rebuilding my mid 70's Motobecane. Still in very good shape. Since I've long since lost my bike shoes, would prefer to get the newer style pedals and clips(?). What are the odds it's a 14mm thread, and how can I verify that just running a 9/16 tap will allow me to use a new pedal?

The rebuild process has not gone nearly as well as I would have liked, my local bike shop has screwed up more things then they have fixed.
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Old 04-24-08, 02:36 PM   #7
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My guess is that my cranks don't use the French threads, they aren't THAT old. A 70's Motobecane probably DOES have the French threads. You could replace the crank, but by the time you're done it will have cost more than the bike is worth.

And yes, I kept my pants on. But the drool is always obvious when I talk to her. We're both married too, and I'd like to stay that way. She'll probably bring her husband along as he also rides.
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Old 04-24-08, 05:05 PM   #8
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Could you possibly have "old French" cranks with 14mm x 1.25 pedal threads, which according to Sheldon can be tapped to 9/16 inch? But where are you going to get a left hand tap?
If its french threaded, you don't need to tap the threads. Just make sure the pedals are going in straight and thread them all the way in. They will be tight, but they will go in just fine. I had a Stronglight French threaded crank that I uses regular pedals on all the time. Many times on and off with no ill effects.
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Old 04-24-08, 06:54 PM   #9
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If you're just chasing the threads you can make your own chasers from a set of old pedal axles. You need to file or grind in about 6 equally spaced gullets with a square file held such that you have a radial cutting edge and a ramped relief ahead of it. Then file or carefully grind in some lead for the first few thread teeth and VOILA! Homemade crank thread chasers that work on aluminium cranks just fine. They are best used with some tapping oil that is meant for aluminium like Tapzall.

I also have no doubt that this option would work well for re-threading the metric French cranks as well. In a pinch I've used such homemade taps fabricated from grade 8 bolts on aluminium where the whole thread needs to be done, not just a chasing or a skim out.

One point though. You will want to start with axles from a better quality of pedal. The better the harder the steel will be. My own came from an old set of alloy pedals with some vintage value other than the fact that the cups and cones and bearing balls were rusted solid and totally beyond redemption.
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Old 04-24-08, 06:57 PM   #10
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I would not count on being able to put on without tapping out. You don't want to find out that you can't get the pedals off again. Being able to thread part way in was a common way for us to suspect french threads in the "old days."
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Old 04-24-08, 07:05 PM   #11
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I would not count on being able to put on without tapping out. You don't want to find out that you can't get the pedals off again. Being able to thread part way in was a common way for us to suspect french threads in the "old days."
I've had some pedal and crank combos where the resistance stayed consistent all the way. For those it was fine. But I know what you're warning about here. The person threading the pedals in MUST be able to recognize the telltale progressive tightening that indicates a thread that's REAL close but not close enough. If

20 TPI compared to 1.25 mm is only .008 inch out per thread and the diameter is "only" .010 out with the 14 being a little smaller. But that smaller diameter combined with the 8 thou per thread means that all but the most undersized threaded pedals will jam 4 or 5 turns in. And as bikeman says it'll press fit itself to a jam shortly after that if you try to force it.
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