Bicycle Mechanics - Rear cog drops with pressure

Hey there, so whenever I change my rear gear to a bigger cog it changes alright, but when I stand up and pedal or start going up a hill (when I need a lower gear) it drops back to the bottom cog; usually causing crotchular pain from landing on my seat trying to regain balance, then me walking up the hill. I can barely put any pressure without it dropping so Im stuck with using 2 gears (my two front chainrings...which only gets higher)

I checked my cassette teeth and they look fine and not much wear. Is this a problem with my rear derailleur or cable/chain tension?

I will be taking it into my LBS but thought I could save $50 from them telling me what one of you may be able to solve and buying whatever needs replacing on top of that.

Thanks in advance!

It moves one gear or the entire cassette? If it's just one gear, it sounds like maybe you just need to adjust the barrel adjuster for the derailleur a couple clicks.

It moves back to the bottom (entire cassette) no matter which gear its at.

Hmmm. How many speeds is the cassette, and what makes/models are all the parts? Friction shifters can sometimes slip if they aren't adjusted properly, but I'm not sure why pedalling harder would cause that.

This is probably a lever related problem, but more can be happening. Need more info:, road or mtb, type of levers, and suspension or not.

One quick possibility which is fairly common on rear suspension bikes is that the housing loop in bridging to the swing arm is too short. Usually this causes a shift to a lower gear when the arm swings enough to pull directly on the cable. But if you're already in low, there's no slack available in the wire so the arm yanks it back from the lever shifting to high, then when the arm relaxes the RD drops back.

This is probably a lever related problem, but more can be happening. Need more info:, road or mtb, type of levers, and suspension or not.

One quick possibility which is fairly common on rear suspension bikes is that the housing loop in bridging to the swing arm is too short. Usually this causes a shift to a lower gear when the arm swings enough to pull directly on the cable. But if you're already in low, there's no slack available in the wire so the arm yanks it back from the lever shifting to high, then when the arm relaxes the RD drops back.
Unless he has a low-normal derailluer, but we don't know enough anyway.

Yeah sorry, its ten speed road bike. Shimano altus headset shifters. 5 speed cassette. Shimano Deore rear derailleur.

Thanks again!

Yeah sorry, its ten speed road bike. Shimano altus headset shifters. 5 speed cassette. Shimano Deore rear derailleur.

Try tightening the friction at the shift lever. There is usually a screw or a "D" ring for this purpose.
Five in the back is normally a freewheel, not a cassette.

Hmm im guessing its probably my shifter loosening for some reason when I put force on the pedal (somehow effecting the cable); creating no tension in the cable and shoving my gear back to the smallest sprocket. I'll fool around with my cable/shifter and report back.

Yeah sorry, its ten speed road bike. Shimano altus headset shifters. 5 speed cassette. Shimano Deore rear derailleur.

Thanks again!

Given that it's 5s, I suspect that it's not index shifting. So odds are that the friction clutch on the lever isn't tight enough. Tighten the small wingnut in the middle a bit to hole better. You want enough friction to hold position, but not so much that the lever is hard to move. Sometimes the clutches don't hold because a washer is missing, or the screw is bottoming before pressing the plates together enough, so you might need to do some investigating if the obvious fix doesn't hold.

Yeah tightening it up and Ill let you know.

Woops.

*freewheel

Yep problem solved, I noticed that the D-ring would get slightly looser and looser as I rode then eventually started the problems again. Tightened it up real tight to avoid this and works without loosening; although its harder to shift, it works great.

Thanks for all your help!

Yep problem solved, I noticed that the D-ring would get slightly looser and looser as I rode then eventually started the problems again.... !

Either of two quick fixes will solve that problem.

Remove the screw and gently pinch one thread with a pair of diagonal cutters, to distort the thread slightly. This will make it somewhat self locking when it's re threaded. If you've never done this before do only a little bit, and test until you find the amount that gives you a bit of resistance.

The other - safer - way is to remove the screw and paint it with rubber cement and let it dry. That'll give you a workable anti-vibration thread which you can adjust yet should stay put.

Either way, ad a stainless steel washer between the wingnut and outer cover. The cover works back and forth with lever movement, and a washer will reduce torque transfer to the wingnut.

There may also be a missing washer in the lever. There's typically a washer with a rectangular hole in the middle that goes over the tip of the shifter-boss and the outside of the lever just underneath the fixing-bolt/D-ring. This washer prevents rotation of the fixing/bolt/D-ring when you flip the lever up and down.