My bike started a weird thing yesterday. Reoccurred today.

when peddling normally, there is a noise and a feeling as if a bear is moving up one or down one.

i look at the grass and I see I’m in the middle gear at the front sprocket and I’m in the 4th gear at the back. I keep peddling and the “gear jump” happens again.....yet I’m remaining in the same gear, still in 4th.

keep peddling some more, same thing. Feels like a gear change/jump, but I remain in the exact same gear.

whats going on?

 

Sounds like a worn chain and or sprocket. Or a bad match like new chain and worn sprocket.
If you measure a 12" length of that chain the 1" marks should fall center of the rivets. As the chain stretches you will get a longer measurement. 1/8" is about the limit. But, the sprockets and cluster have also been wearing. Riding in one front to rear combination most of the time is the worst.
Another place to check it by pulling the chain away from the F sprocket. New with no wear they will be tight. Also look at the teeth. If they are worn the valley will be wider.
Bud

 

Thanks. I’ll have a look. Bike is a few years old, but rarely used.

 

Also check for frozen links. Old and not used could be some links are not flexing. If you hold the rear wheel up and rotate the crank the derailleur would likely jump as the stiff link/s pass through.

Bud

 

I'd look to derailleur adjustment. Cables stretch as a matter of course and in the doing change derailleur 'tuning.' If the cable has stretched enough to mess up the tuning, the rear derailleur will be moving outboard from the bike frame enough that the chain can make noises like it's trying to shift onto the next smaller cog but it's just not quite moving far enough for the chain to mount on that smaller cog.

I tune gears with the bike standing upside-down on the saddle and handlebars because the lets me spin the cranks and run through the gears without the bike going anywhere. I put the rear derailleur in in the middle cog, or either of the two middle cogs if you've got an even number of sprockets. And if you've got a triple front derailleur, it also should be on the middle chainring. Then turn the barrel adjuster to change cable tension. What you're looking for is that the rear derailleur will shift from the middle cog to both the one up from it and the one down from it with equal ease.

If my guess is right, probably a half to a full turn of the barrel adjuster should reduce if not eliminate the problem.

The tuning will change slightly when you stand the bike upright because of the flexing of the frame and load on other components so it still might need a bit of fine-tuning when you ride it. The key is to have just the right amount of tension on the shifter cable that whenever the chain is anywhere near the middle of the gear cluster it seems to be equally eager to shift up or down.

 

Fred is on the right track. I've had thsi issue many times. Derailleur adjustment is key. Cables stretch and are affect by weather and season.