What causes a chain to jam?

jeepie

Cycling home on my 105 equipped road bike. Changed from the big to the small chain ring at the front and big sweep to do 3 sprokets down on the back. Chain jams. AAARRRGGH. I was doing about 20mph at the time....

I think this may have been caused by my gear indexing being out after a freehub change.

I've reviewed

http://www.youtube.com/watch?v=SkzvfCaIbyQ

So here's what I notice. When I do the big sweep to change 3 sprockets at the back (lever position 3 here > http://techdocs.shimano.com/media/techd ... 621374.pdf) , there is a ticking sound. If I change up a single click the ticking goes away. Could this be why my chain jammed?

I think I need to rotate the rear derallieur adjuster barrel to fix it, but I can't work out - is my gear cable too slack or too tight? So clockwise or counterclock respectively. Any tips appreciated.....Should I do an 1/8 of a turn each way and suck it and see?

Cheers

J

cjcp

When my chain jammed, the chain links were stiff, so they didn't sit on the teeth properly. This caused a real problem when the chain travelled through the rear mech. I loosened it up with oil.

Alternatively, are any of the links twisted/bent?

jeepie

Cheers cjcp. Will give it a good lube up in the morning and try again....haven't been oiling the chain quite as religiously as went I was just using the bike for weekend rides. Then I'll check the links. Then I'll try twiddling the derallieur knob!....

Happy commuting....

stevedb55

Jeepie,

I've got 105 on my Cross bike, found the same issue if I try to change gear from large to smaller front chainring it was locking up , seems to mainly happen if I'm on a higher gear on the cassette (think its called crosschaining??) If I change down on the rear cassette, to one of the middle cogs, then I can change down on the front chainring - does that make sense?

Cheers
Steve

jeepie

Very interesting, Steve. I've heard (but not read) a lot about cross chaining i.e. there are certain combinations of gears that you are not supposed to use....At this stage in my learning curve I don't actually know what rear sprocket I'm in. I just change to what "feels" right..... I'll definitely keep an eye on this to see if it occurs in a particular combination of gears. Cheers for the tip!

Deadeye Duck

stevedb55 wrote:

Jeepie,

I've got 105 on my Cross bike, found the same issue if I try to change gear from large to smaller front chainring it was locking up , seems to mainly happen if I'm on a higher gear on the cassette (think its called crosschaining??) If I change down on the rear cassette, to one of the middle cogs, then I can change down on the front chainring - does that make sense?

Cheers
Steve

Kind of like this?
http://www.youtube.com/watch?v=8iGH_6pwgow

jeepie

Wicked. That is clear as crystal. Just off home on the Bianchi so will give it a whirl. Red Dragon told me something similar a while ago about climbing hills but hadn't thought about it on the flat...........Cheers chaps.......Will keep you posted!