Old 15 speed drivetrain - uneven feel on smallest cogs when pedaling
 

Hi,

I am fixing up my 30 year old touring bike for sale. It's got a triple crankset and a 5 speed gear cluster on the rear. 30, 46 and 50 tooth chainrings up front. The rear cluster goes from a 32 down to a 15 tooth cog. It's an old Shimano gear cluster and an older Shimano Deore derailleur of the same vintage.

I haven't ridden it in many years. As I was cleaning it up, I noticed that when I ran the chain in small in front and small in the rear, the derailleur was horizontal and the chain actually hit the cage of the derailer when pedaling. Never noticed it before, but then again, I never used that combination.

I decided to take out three links. I pre estimated and when I ran big up front and big in back when holding three links out, the rear derailuer was at 45 degrees and when I ran the little in front and little in back, the derailleur was no longer horizontal and the chain no longer hit the cage.

I removed the old links and then reconnected the chain and now I notice almost like a dry bearing sensation)don't know how else to describe it) when I pedal and it only happens when the chain is on the two smallest cogs in the rear. It's barely noticeable when I turn the cranks on the rack. It's really noticeable when riding, now.

Observationally, when the bike is on the rack, the wheel spins and I can see the cluster has a sort of minor wobble and it drags against the inner circular chain guard that is sandwiched between the gear cluster and the spokes. Not sure if that's relevant.

When I ride in the middle chainring and the middle rear cog, I don't feel the sensation at all.

What do you think it is?

FYI, the derailuer hanger appears to be lined up, but I don't have a tool to verify it. The middle chainring is really worn out. The chain has to be stretched and the upper pulley on the derailleur has big gaps between the teeth. The chain probably has about 3 thousand miles on it.

Without replacing the entire drivetrain, which I don't want to do, because it's half the value of the bike. Could it be something less major?

Thanks.

Seems to me from this distance that the chain and/or cogs are getting worn. As they wear the mesh gets rougher. First noticed, usually, on the small cogs and/or the one that gets used most. Another possibility is that the pulley wheels are worn but that usually is felt on all the cogs. The reason the work stand test is smoother then riding test is that the tension on the chain, from pedaling pressure, pulls the chain up tight against one side of the teeth as well as pulls the chain bushings/pivots apart the most. these forces are not present when on the work stand.

Given that you state that the chain is own out (as well as other drivetrain parts) I think you have the most likely answer already. The solution is also already stated. Replacement of any and all worn parts. Why fight it? Andy.

Removed three links, eh?

Before you ride that bike again I would urge you to GENTLY attempt to shift your drivetrain into the large chainwheel/large cog combination while pedaling by hand. If you encounter any resistance STOP, your chain is too short. If you inadvertently shift to that combination while you are riding you may do extensive damage to the bike.

As you stated:
Cross chaining
Too short chain
Worn out drivetrain

You have the trifecta -- any one of the above is sufficient.