RacerOne

We had a snapped off derailleur on the trail. I removed the derailleur, shortened the chain to run the middle cog on front/back and reconnected the chain with a quick link. It all looked pretty pro. However, the chain would continually try to climb to the next larger cog on the back making it so the chain tension was so tight it was next to impossible to even move the cranks. Any ideas where I went wrong?

Thanks!

Coal Buster

Assuming the gears were aligned properly in the first place, it sounds like frame flex was the culprit.

dsbrantjr

There is only one cog which naturally "wants" to align with a given chainring; you chose the cog next to that one, which is why the chain "insisted" on moving over. You are fortunate it did not do any damage in the process, the forces can be surprisingly high.

Bill Kapaun

I agree about finding the cog it "wants" to line up with. IF it then shifts to a smaller cog, no damage.

SparkPlug

This is in many respects why I read these forums, for the insight. At the risk of getting slapped wristies for the rob that makes so much sense that I will mention 'chainline'. Naturally the first hit via Google is...

All About Bicycle Chainline

I think the other part of it is cross-chaining which you should avoid. Otherwise I will go off on a probably wrong tangent.

Your rear dérailleur is set up to feed the chain into the bottom of your cogs. If it is indexed then it has to align properly with the selected cog at the bottom. If it is friction you wiggle the lever to make it so. Bit of subliminal and it becomes natural.

Now introduce 'hyper-glide'.

If you look at your cogs then you will see that someone has included a stepped profile on the external face of them below the teeth. That helps to lift the chain up when you change gear.

So... taking what dsbrantjr says you have two things. The chain wants to naturally align with a chainring/cog combination but with 'hyper-glide' messing about with stuff even if it looks like it aligns better with a lower cog you should be better off choosing to set things up with the next cog up because that 'hyper-glide', given a chance is going to try and pull it there.

fietsbob

+1, the ramps punched in the sides of the cogs, and short gate teeth are designed to make the chain eager to ghost shift like it did .
that is what the engineers have done in the last 30 years .. design those details.