vol

My rear derailleur has 7 speeds. Whenever it is on the lower gears (3 or 2; I almost never use 1), the pedaling immediately becomes very rough (not smooth), and there are apparent rough clicks with each pedaling movement (seems always when right pedal going down). The pedaling feeling resembles somehow (but apparently isn't) as if there are some "knots" on the chain or the cogs. All gears above 3 are smooth. What should I check for possible cause?

As always, all replies are appreciated by this newbie.

Andrew R Stewart 

Check for- Worn out front and rear cog teeth, worn out chain, worn/bent/twisted rear der and pulleys, poor gear adjustment/cable tension, poor chain line, bent ot twisted cogs or teeth, worn out bearings in hub, pedal or crank, worn or loose crank arms or BB in frame, loose pedals.

It's a long list. Without more specific details pretty much anything that moves or is in play when you pedal could be the cause. Andy.

FBinNY 

Could be a long list of possibilities, from misadjustment to wear.

Given that it's affecting the larger sprockets, it's possible that the B-screw is mis-adjusted and the upper pulley is too close to the sprockets, possible even touching through the chain.

Also, having followed your prior posts, it's entirely possible that the trim is off.

The above are by way of starters, I (we) can't tell you more without specific info, and even then it's nothing like having eyes on the RD. There are a number of good shops in Manhattan, but the price for a basic derailleur adjustment varies tremendously, so shop around.

One I tend to forget, but who has good service and low prices for the basics is Frank's, on Grand Street. Also, consider my earlier advice and find which of these are offering repair classes, either free or for a nominal fee.

vol

Frank's was where I bought this bike! Yes they are nice folks, and I like their location to be just off the East River Greenway.

The pulley is not close to the cogs and no touch at all. Since both you and Andy include the cable to be among possible causes, perhaps it is. I checked the cog teeth etc. and didn't see anything not normal (I never abuse my bike). Interesting thing is that the rough feeling occurs only when I'm on the bike riding; if I pedal it by hand when doing maintenance at home, it doesn't occur.

Since I made a little adjustment today, I'll see if there'll be any change when I ride it next time. In case you are not aware or forgot: this Saturday is the Summer Streets day in NYC, Park and Lafayette avenues will be all bikes/pedestrians. There will be some free bike services along the way including Bicycle Habitat, though last year I saw they were very crowded with people lined up for the free services, so I may still go to the Frank's on a weekday (they are always too busy on weekends).

Thanks to both.

ThermionicScott 

By "lower gears" do you actually mean the smaller cogs (it's not clear which way they're numbered)? Some vibration is normal with these, it's the nature of the beast.

vol

No, I mean the larger cogs in the rear, closer to the bike's body. The rough feeling and noise are very obvious and not normal, and follows the pedaling cycle, felt by the right foot.

I was just thinking why the problem doesn't show up when I hand pedal it at home on the same lower gears, but only shows up when sitting on the bike and riding. Perhaps it does have to do with the B-screw: perhaps when riding uphill (that's when I use the lower gears) with force, the chain gets more tension and the pulleys are more up close to the cogs and may have touched the cog, but when manually pedaling at home (without a bike stand, so I could do it only briefly), the chain is looser, so the pulley stays low and doesn't touch the cog. I screwed in the B-screw and will see if the problem recurs on my next ride.

Andrew R Stewart 

When the bike is on the stand the chain is meshing with the cog teeth with only the force of the der pulley cage spring, not too much tension at all. And this tension is pulling the chain links into the depths of the teeth.

When you are riding and pedaling the chain is being pulled against one side of the teeth only. And pulled with possibly great tension. So both the chain's rollers and the teeth are engaging off center so to speak with the tension driving the parts to contact onntheir sides.

This difference in how things work with no tension and with tension is part of the every day assessment process, in a shop. Some of the with tension state can be replicated with a partial application of the brake, when the bike is on the stand. We use toe clip straps for this, wrapped around the brake lever and bars. But this is only a partial replication. Nothing beats a test ride by an experienced wrench. Andy.

vol

At home I don't even have a bike stand (I once bought one but it didn't work), so I just lift the back of the bike when trying to pedal manually, extremely awkward and I could only do it for few seconds each time! (Once I slipped and me and the bike both fell to the floor )

Andrew R Stewart 

vol- Can you loop a couple of lengths of rope or cord from above the bike? If so then a loop at the bottom of the cords can sling the seat and bars/stem, lifting the bike off the ground. Andy.

vol

Unfortunately I don't see a way. It's an apartment building and I don't feel like drilling a hole on the ceiling or wall to install a hook. Is there a good easy-fitting bike stand that works for most bikes? The one I had at the link above had some good reviews but doesn't work for me at all.

Andrew R Stewart 

vol- The problem with bike stands is how they interface with the bike. The rear axle ones (like a trainer stand or the display stand you tried) are dependent on a classic QR end cap which are rounded or axle nuts. Modern external cam Qr don't play nice with them, although it is simple enough to trade out the low retention external cam QR for an internal cam with rounded end shapes. The stands that lift the bike by the BB underside (usually with a hook that goes over the downtube) (https://www.jbimporters.com/web/check...t_number=92669 ) need a BB shell w/o interfeering cable guides and a DT that fits the hook. The stands that use the crank arm won't allow pedaling. The stands that hold a wheel ( https://www.jbimporters.com/web/check...t_number=93884 ) don't allow pedaling. The stands that hold the bike by the ST or the post (https://www.jbimporters.com/web/check...t_number=62057 ) are the best for actually working on the bike but are the most costly. The stands that hold the bike by the TT (like a cheap car rack) can work if the bike fits them but tend to be big units that lean against the wall or small ones that get screwed into the wall. Having turned a wrench professionally since high school I am spoiled and use Park's stands. Andy.

vol

I rode today. Still had the problem (felt the very rough clicks on both feet, though more on right foot, and there's the ugly noise). I still think it's the pulley touching the cogs (otherwise why it occurs only on lower gears). But I have already turned the B-screw quite tight, only a little bit left. If I turn it all the way completely in, probably not good?

Andrew R Stewart 

vol- The B screw can be turned in all the way w/o problem. But there are times when the guide pulley will still touch the cogs. Shimano doesn't use upper knuckle springs with much tension. When pushing the limits of cog size, chain length, rear drop out dimension that upper spring might not be strong enough to pull the der back and attain pulley/cog clearance.

The B screw can be removed and reinstalled from the tab's other side only enough to hold the screw in place. This effectively lengthens the screw by the head's thickness. the screw can be replaced with a generic longer one. The chain's length can be shortened a link pair, making the der cage rotate a bit more and results in the pulley moving down and away from the cog. BUT this might make the chain too short for the big/big crossover combo. This needs to be carefully tested before riding. Nothing wrong with a too short chain if the rider NEVER tries to shift through the big/big. Fat chance that this will never be done, I don't suggest this solution be used but be known of. The cog size can be reduced, of course this also changes the low gear. The front rings can be changed but again the gearing will be different.

The best solution is to replace the der with one that has the correct index compatibility and a greater range of cog size acceptability. And then play with chain lengths. Andy.

vol

Andy, thanks for the information. Since I'm a terrible layman, looks like I have to make a trip to my LBS to solve the problem. Today I went to Bicycle Habitat where they were offering free bike adjustment/repair as part of the Summer Streets event. It was few minutes before the conclusion of the event, so the shop guy seemed not to want to bother too much. He made some adjustment of the cable and told me it's fixed. I rode around, still had the problem, went back to him, he adjusted cable again, said ok; I rode, still had the problem.

vol

Yesterday I turned the B-screw to the end. When I rode super slowly for a few yards with super light pedaling on flat road, no clunky clicking (which seems a small improvement), but with the slightest increase in pedaling force, the problem was back, so it seems to me the B-screw made some difference, even if there are other factors.

Before I have a chance to visit the bike shop, I might try replacing the B-screw with a longer one. Will any longer screw of the same diameter do? Can't be too long, though? Sorry if the questions sound unbearably stupid.

cny-bikeman

See Andy's post above - you can turn the screw around. A new one needs to be the same (metric) thread as the original.

vol

To turn it around, I'll need to open the derailleur (to put in the screw from inside out, I think that's what you and Andy mean), which as a stupid newbie I don't feel comfortable doing, lest messing up anything or failing to reassemble properly. Bottom line is I have never dissembled anything on my bike except the brake pads.

ThermionicScott 

vol, what rear derailleur and cassette/freewheel (specifically, how big is the largest cog) do you have? Can you post a picture? I'm wondering how turning the B-screw in all the way isn't fixing this.

vol

Shimano MF-TZ31 7spd MegaRange (14-34t). Photos: