Losing a pedal? Sort of a survey.

[TahoeDirtGirl]

This is like an engineering question!

I had this happen to me actually because it was the right pedal and you know how confusing that can be putting them on (lefty loosey righty tighty oh wait...not on these pedals!). What I think happened was that I tinkered with mine and cross threaded the pedal. What happens with cross threading is that only part of the threads are crossed while you will have a viable run of threads otherwise. If it did get cross threaded it may not have been tightened enough or it was cross threaded enough that it would just start undoing itself because the threads weren't doing their job. That would explain why no one could get it to budge at the mechanic because at some point, the threads get really fused and it takes alot of cussing to get it to move.

And then there may have just been a difference in the pedal due to manufacturing. Just a little off on thread size and a little grain of sand can cause alot of problems. So that is why you want to always clean off the pedal and the crank before assembling them and take your time when putting them on. And if they aren't going right, don't force it. That is what I found with doing the right one. They just don't go on right and it takes alot of patience.

[VeloVT]

This is like an engineering question!

I had this happen to me actually because it was the right pedal and you know how confusing that can be putting them on (lefty loosey righty tighty oh wait...not on these pedals!).

I have a personal bike maintenance crusade and it is to get people to stop thinking about "left" and "right" when installing pedals... think "forward" and "back." Of course, with some pedals, you need to make sure you are working with the "correct" pedal (e.g with road pedals, you'd never even try to put the right pedal on the left crankarm because it would be obviously backwards, but with, say, eggbeaters, you have to check the marking on the pedal). But in terms of which way to install them, both pedals go ON by turning the toward the front of the bike, and both pedals come OFF by turning them toward the back of the bike. If you think of it that way you don't have to remember which one is "lefty-tighty."

That said, I've never had a pedal strip out, but I've had lots of cleat screws that don't want to stay in or stay tight, even though they are not stripped. Arrgh. Suddenly noticing your cleat is loose while you're riding is frustrating.. especially if, upon inspection, it turns out that the offending screw is GONE...

[aicabsolut]

I've seen pedal spindles break, crank arms break, pedals break, and crank arms come loose, but I've never heard of anyone I know have an issue with pedals unscrewing themselves. The reason for the different threading on each side is that the action of pedaling is supposed to tighten the pedal. So you should definitely not have to stop periodically and keep tightening the pedal. Just pedaling should do that for you.
Bizarre. I can't believe it happened with 2 different cranks!

[TrekJeni]

Honey just asked "what cha doing?" and I read him your story. He's been wrenching for more then a decade and is the manager of his family's shop.

He's never told anyone to tighten their pedals five hours into a ride. He says they probably aren't using pedal washers and now even though the pedal still looks good, it's not. He would have demanded all new parts.

Put some new pedals in there and see if the problem goes away.

Hope this helps.

Jeni

[Grog]

Thanks everyone for your detailed answers!

I increasingly think there is a problem with the pedal. The reason we haven't changed it yet is that the other pedal is fused into the other crank, and I don't think we have an identical R pedal sitting around, or even another SPD pedal. Of course we could get another one, but while we're at it I think we'll just change the other crank and get two new pedals.

Now: would you give the new setup a chance or would you change all parts NOW to avoid further troubles?

[aicabsolut]

I would change all parts. He's lucky he hasn't had a bad crash already from losing a pedal.