I am rebuilding a trek 800 antelope, and having some drivetrain noise. under load there is a click/clunk noise that occurs randomly. I just repacked the hub (even though the cones are a bit damaged and I need to get new ones, it spins mostly freely with just a little bit of drag on a couple spots) and put on a new chain. It does not make any noise once you stop pedaling, or pedaling backwards. If I reduce chain tension by physically moving the derailleur, it seems to quiet down. No difference changing chain rings, but the smaller the cog, the louder the noise.

i have not tried riding it yet, this is just an on the stand diagnosis.

I cant tell if it's coming from the crank or the freewheel/derail. The crank arms are tight, and the bb is properly adjusted. The crank is a biopace (could this be my problem?).

any ideas?

thanks in advance

See: https://sheldonbrown.com/creaks

By the way, there's no such thing as a "Biopace crank" but that's not it in any case.

Sheldon "https://sheldonbrown.com/biopace" Brown

Some hints to hunt it down:

Is it every other pedal
Is it on the power stroke
Does it do it {When you are coasting Get off the saddle hop up and down on the cranks}
If you have another set of peddles replace them, will it still do it?

THE 1ST PLACE I ALWAYS GO TO = Tighten the crank arms on both sides / Check the chainring bolts / Oil the chain.

The Bottom Bracket is old school with loose bearings. Which should be overhauled every year no more then 2 years. Pretty sure you have no grease and rust on them.

I have more thoughts. These are the common ones

the noise has no apparent pattern. It does seem to happen more than once a revolution, sometimes several times in succession within a revolution. I am leaning towards the bb, and will repack it tomorrow.

Yes, I know there is no such thing as a biopace crank, its bio pace chainrings.

When you take out the BB, pull it out slowly and make sure all the bearings stayed packed. Sometimes bearings will fall out without realizing. Also, grease them heavily. If none of those things work, make very sure it's the BB and just spring for a new one. They're not very expensive.

You mentioned that the BB cones were worn and need to be replaced. I'm guessing that's your problem and you're getting the "clunking" noise when you put more tension on the chain. That's why it's louder in the higher gears.

If I'm right a Shimano UN54 cartridge bottom bracket will fix it. Make sure that the shfll width and spindle length match what you have now. It should cost between $20.00 and $25.00.

it was actually the hub cones that need to be replaced. I threw on a different freewheel and the noise is gone! i'll still repack the bb probably.

thanks everyone