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Losing a pedal? Sort of a survey.

Grog2010-04-28 18:05:16 +0000 #1
SHORT VERSION:

Survey question:

Have you ever had a pedal come off the crank, leaving you with a pedal clipped into your cleat but not attached to the bike?

Bonus question:

Can you tell me a litte about the circumstances?

LONG VERSION:

Background:

My sweet partner is riding the mountain bike that used to be his dad's to go to work, about a 60 km round trip every day. It's quite important that the bike stays together until destination because he's not really riding near transit services. The mountain bike was only lightly ridden by his dad for a few thousands of kilometers on local trails. The pedals are Shimano SPDs of the most common kind, cranks initially were Deore.

In August, he literally "lost a pedal" (pedal came off the crank, stayed clipped to his shoe). First time, he put it back in. It happened again a second time the next day, again he put it back in and brought the bike to the shop. Note: the other pedal is literally fused into the crank and cannot be removed by anyone with any amount of force. Mechanics attribute the problem to the salty air (the trail his dad rode is along the water).

Shop mechanics, an older guy I tend to respect, finds out the thread in the crank is basically stripped. My partner and the mechanics together decide that the best idea is to replace the crank. Can't find a Deore crank so a LX crank goes on.

Yesterday, a few hundred kilometers after the repair, pedal comes off the crank again. There are small metal bits in the pedal hole on the crank, husband thinks the thread is stripped again. Can't put the pedal back on this time. Thankfully that's on the way BACK from work so I end up picking him up and we bring it back to the mechanics.

Mechanics cleans the hole and gets the pedal back in. He says the thread is NOT stripped but that my partner should have tightened the pedal after about 5 hours and then again after 10 hours to prevent this problem. My partner finds this ridiculous as, in his 300,000+ km riding life he's never had a pedal come loose. This morning he's off to work and I'm praying that the pedal doesn't come off because I'll have to do a rescue in my pajamas if it does, and I have no precise idea of where to find him if he calls!!

Any word of wisdom on the pedal/crank relation?

Any help is appreciated, as this is pretty crucial for him to get to work safely and on time.

Thanks a lot.


Eden2010-04-28 18:20:58 +0000 #2
On my utility bike - that I was swapping pedals on quite a bit (I did not have enough pedals for all my bikes!), sometimes one of the pedals would do that. I'm not totally sure why - and it was stolen, so I'll never find out..... It was always the same side, so I think it was from a combination of not tightening it down all of the way and some thread stripping - but they are supposed to be threaded so that pedaling motion actually screws them on, not off!
DebW2010-04-28 18:16:16 +0000 #3
Grog, as far as I know, pedals pulling off is pretty rare. However, since the same pedal has come off of two cranks, at this point I'd replace the pedal. That pedal may be a slightly smaller diameter than it should be, or have improperly cut threads, causing it to not be secure in the crank arm. I do know that Campy Records cranksets in the 1970 came with very poor threading, and we learned to run a tap through a brand new crankset before installing pedals. I know one person who crashed when a pedal pulled out of an expensive Campy crank in the mid 70s. Recently, having worked in a bike shop for 3 months now, I've seen 2 pedals strip out of cheap department store bike - but likely those bike were never assembled correctly in the first place.
Crankin2010-04-28 19:08:26 +0000 #4
This happened to my son, during his first year of road riding. It was on a lower end Fuji road bike, with spd pedals. I don't know what caused it, but it happened as he was sprinting across Rt. 2, a major highway, on Rt. 62, here in Concord. However, at the time, we lived about 9 miles away.He slid across the highway as the light was turning yellow and severely sprained his foot. He was sitting on the curb, crying in pain, when a doctor from the nearby hospital stopped and helped him and gave him a ride home. I was pissed he took a ride from a "stranger," but it did force me to buy him a cell phone.

Every time I cross the highway in that spot (which is often), I think about this.
TahoeDirtGirl2010-04-28 19:50:30 +0000 #5
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.
VeloVT2010-04-28 18:32:16 +0000 #6
Quote:

Originally Posted by 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!).

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...

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