Help me out so I donít have to schlepp this beast back and forth to the dealer. The bike is a 2002 KHS Tandemania Milano. Components are Shimano 8 speed 105 STI. Rear wheel spacing is 160 mm.
This is what happens:
Occasionally, when standing and climbing, the cranksets will just lock up - unable to pedal - on the downstoke. You have to quickly backpedal to free it up, and then you can pedal again. The first time this happened, it caught me completely off guard. We were climbing a short, steep Ďsprinters hillí in the middle ring/big rear cog (42/26). The chain locked up and we lost speed so fast I lost my footing coming to a stop and dropped the bike and my gurl!
I figure the problem is some sort of chain suck. But, I canít see what is going on at the back crankset, so I am not sure. I checked the chain and could find nothing wrong with it, but replaced it anyway. Thought I cured it until a few weeks later when we were standing and humping up a super-steep little number in the small ring, maybe 2nd or 3rd cog on the freewheel when it does it again. I stop us without dropping but we have to walk up the dang hill!
So, I email the shop and the owner thinks it is the shifting ramps/pins on the 105 chainrings catching the chain. He says any burr on the chainring can cause suck. Now, the granny does not have any ramps. But, I replace the middle and big rings with plain chainrings and take a link out of the chain. But guess what? It does the same thing! Just last Sunday we had a good big-ring roll on a flat section of road. A little rise is up ahead, so when we hit the bottom I shift down 2 cogs so I am in the big ring/3rd cog (53/21). We stand and start climbing and the thing just locks. Since we are rolling at about 18 MPH, I call for a backpedal which frees the chain and we continue on. I stop at the top of the hill and examine the drivetrain, but canít find anything wrong. The only time this has ever happened when seated on the bike was one time when we were really hauling arse on a bumpy flat road.
What could it be????
EDIT: Writing this got me thinking, so I checked the bike out some more and I am not sure that chain suck is the issue. There are only 2 small scratches on the drive side chain stay, no big gouges like the chain was getting whacked against it or jammed against it. I wonder if the cassette could be the problem or maybe the rear hub. The hub is a Shimano tandem hub with a plain threaded axle. Could the axle be bending? The cassette binding???