Bicycle Mechanics - MTB Cassette Problems

I'm a bit of a bike mechanic newbie so would really appreciate any help :)

I have a Iron Horse hardtail, and my rear cassette has 8 gears. Now whenever I try to shift up into my 6th gear, nothing happens (or in rare cases where the chain does catch, there can be a 10-20 sec delay). I can shift into all my other gears fine (1, 2, 3, 4, 5, 7, 8), just 6 has problems. Also I can shift down from 7 and it catches 6 right away (which is what I've had to do when I'm in 5 but want to shift up).

I bought my bike at a store that doesn't specialize in bikes, so they shrugged their shoulders and they did the free tune up (within 1 year of purchase, only includes brake/gear adjustment, and minor truing).

Just thinking, I've ruled out these possiblities:

1. Possible damaged teeth on 6th gear - I dont' think this is the case because I always consistently have this problem.
2. Bent gear? - I'm not sure about this possibility... by my human eye the gear appears straight.. and even a slightly bent gear should still work part of the time (considering I can shift down into it)

Is it possible that my rear derailleur somehow can have a problem with just one intermediate gearing?? It seems strange to me.. as all my other gears switch fine...

Does anyone have any experience with this problem? I'd take my bike to an actual LBS, but the tuneup would cost like 1/6th of my bike's value... lol might as well save up for my next bike :P

Appreciate any help!
-xan-

did you buy the bike from Sport chek? How long have you had it....because if you say that its always been like that they may exchange it or something. I dont have a realy answer on how to fix it but im sure somebody will. and if they dont then i would just take it to the lbs and im sure they can help you out.

Typically if the cable tension is off, you will have that problem in a few gears, but if the derailleur hanger is just slightly bent it sometimes only happens in one gear, often times around the middle of the range it seems. Could really be any number of things though. Sometimes cheaper bikes just don't shift 100% no matter what, it seems.

Two big things:

1. Is your drivetrain clean?

2. Lubricated properly?

I can't tell you how important those two are to a well running drivetrain. Its ALWAYS the first thing I do working on a bike, and cleaning everything out can radically change the shifting.

You shouldn't need a tune up by the way. Just take it to a shop and say you need the rear derailleur adjusted. If the hanger is bent any good shop should be able to easily bend it back, worst case scenario its $11 for a new one. Derailleur adjustments are $5-10 depending on the shop. If you don't know what you are doing you can just make it worse pretty easily.

i have the same problem... the bike tends to skip 5th... its alivio so its not that bad. i checked the derailer adjustments.. and theyre good... it is perfectly straight on 1st and 8th. i powersprayed the derailer to clean it some... and it worked for a short while.. now its skipping 5th again


more reasons for me to turn it into single-speed :D

Oh I should add, I have a Shimano Altus rear deraileur. And an important piece of info I neglected to mention is that the gear DOES work when theres no weight on the bike (on a stand or when the bike's upside down). I weigh very little (~120lbs) but once I'm on it, the gear doesn't catch at all.

Thanks for the reponses so far!

RobotSonic, I purchased it about 8 months ago, I'm pretty sure any warranty on parts is finished, but I will have to check on that.

Sounds like the rear derailleur needs a slight adjustment. On the derailleur there should be a little plastic knob with a cable running through it. Give it a quarter turn (can't remember which direction) and see if that helps. Just count how many notches you turn it, so you can return it back to it's original position if necessary.

CHEERS.

Mark

Shift to the smallest (11) rear gear so that there is no tension on the cable. If the cable has a lot of tension, turn the cable adjuster at the shifter clockwise. If it has very little tension, turn the adjuster counter clockwise.
To finish the job, run through the gears. If its slow moving to larger plates, turn the barrel adjuster on the rear deraiieur counter clockwise. Reverse that for the other direction. Don't mess with the 2 limiter screws.

Shift to the smallest (11) rear gear so that there is no tension on the cable. If the cable has a lot of tension, turn the cable adjuster at the shifter clockwise. If it has very little tension, turn the adjuster counter clockwise.
To finish the job, run through the gears. If its slow moving to larger plates, turn the barrel adjuster on the rear deraiieur counter clockwise. Reverse that for the other direction. Don't mess with the 2 limiter screws.

Check out the Barnett manuals (http://www.bikeforums.net/showthread.php?t=38747)

Hmm, I would think the warranty should be good for a year on components. And it's possible that that cog is simply bad. They're made with special surfaces to aid in shifting from one cog to the next. These surfaces are machined in particular places so that, when the cogs are put together on the freehub, they're in "sync" with one another. What makes it impossible to goof this up at assembly is the fact that the splines on the freehub and on the cogs are such that you can only put them on in one "clock" position. Ya can't even put it on backward (AFAIK). But imagine if the cog was simply machined wrong? That is, the ramping surfaces and the splines are not in the right relative position. Sorta like a coin that's minted with the two faces not quite exactly upside-down to one another. Except it has collector value; this cog would be scrap. Another possibility is that the wrong spacer was put on either side of this cog.

In any event, an easy test back at the shop would be: put another wheel with the same cassette on the bike and try it. If the problem persists, it's in the derailleur, shifter, cable, etc. If it goes away, it's def. the cog or the cassette.

I doubt it's the left-right adjustment of the derailleur (which a cable adjustment would affect); you'd have more problems than with just this one cog. It's remotely possible that there's something foreign in one of the pivots of the der, or just a "sticky spot" within the body, making it difficult for it to pivot to the exact position for that cog. It wouldn't manifest itself shifting from the smaller cog, becuase you're pulling on the cable to effect that, rather than letting the der. spring do the shifting. You'd think the "tune up" at the shop would've included lubricating the pivots. If it did, and it's persistent, the sticky spot may be a manufacturing defect in the der.

xanatos, you may simply be expecting a bit too much from a bike that came from an outlet store and was probably built by a person who's paid on a per-piece basis. They often use SunRace or Falcon freewheels and shifters to save money, and the shifting may not be as good on these.

I also find it interesting that the adjustment changes when you sit on the bike... is it a rear-suspension model, by any chance? How about the rear hub, does it have bearing play (try pushing the rim back and forth laterally up by the brakes and see if it has some bearing slop, which translates into cog slop on a freewheel-equipped bike)?

Thanks for the replies everyone. I'm kinda new to this - heh picking up the terminology as I go. I played around with the barrel adjuster on the rear derailleur (as some advised), but to no avail. More than two twists in either direction will disable certain gears. But yeh since its just one intermediate gear, I dont' think its cable adjustment.

I would try out the cassette on another bike.. if I had another bike. lol

Clean drivetrain? Hmm that's something I want to do this weekend. cleaning the chain is fairly easy, but I have trouble getting to all the grit in the front gears (there a better name for it?) and stuff, do you have to take it apart? Or OK if I were to hose lightly and toothbrush or something?


xanatos, you may simply be expecting a bit too much from a bike that came from an outlet store and was probably built by a person who's paid on a per-piece basis. They often use SunRace or Falcon freewheels and shifters to save money, and the shifting may not be as good on these.

I also find it interesting that the adjustment changes when you sit on the bike... is it a rear-suspension model, by any chance? How about the rear hub, does it have bearing play (try pushing the rim back and forth laterally up by the brakes and see if it has some bearing slop, which translates into cog slop on a freewheel-equipped bike)?

Heh yah it is an entry level bike that's for sure! Its a hardtail actually, um link to the 04 model is here (http://www.ironhorsebikes.com/products/intermediate/maverick_comp.shtml) [ironhorsebikes.com]. Um I think I tried what you mentioned (lifted up rear end, gripped hub near brakes, and wiggled in direction perpindicular to frame), doesn't seem to have any play with it.

Thanks everyone! Appreciate all the helpful folks. Guess for now when I'm in 5th, I just double shift and then shift back down... lol. But will try cleaning and lubing everything.

-xan-

Thanks for the replies everyone. I'm kinda new to this - heh picking up the terminology as I go. I played around with the barrel adjuster on the rear derailleur (as some advised), but to no avail. More than two twists in either direction will disable certain gears. But yeh since its just one intermediate gear, I dont' think its cable adjustment.

I would try out the cassette on another bike.. if I had another bike. lol

Clean drivetrain? Hmm that's something I want to do this weekend. cleaning the chain is fairly easy, but I have trouble getting to all the grit in the front gears (there a better name for it?) and stuff, do you have to take it apart? Or OK if I were to hose lightly and toothbrush or something?



Heh yah it is an entry level bike that's for sure! Its a hardtail actually, um link to the 04 model is here (http://www.ironhorsebikes.com/products/intermediate/maverick_comp.shtml) [ironhorsebikes.com]. Um I think I tried what you mentioned (lifted up rear end, gripped hub near brakes, and wiggled in direction perpindicular to frame), doesn't seem to have any play with it.

Thanks everyone! Appreciate all the helpful folks. Guess for now when I'm in 5th, I just double shift and then shift back down... lol. But will try cleaning and lubing everything.

-xan-

I wash my parts in the dishwasher typically, works wonderfully. BUT if you get some Orange based degreased (biodegradable and effective) and hose down the chain, chain rings, cassette etc with the stuff, then carefully clean the chain, chainrings, jockey pullies (on the derailleur) cassette, etc with a toothbrush and hose the whole thing off after that it will do wonders. Remember LOW WATER PRESSURE!!! You don't want water getting in the seals of the bottom bracket.

I would try out the cassette on another bike.. if I had another bike. lol Actually, my suggestion was that the shop do this, as part of honoring the warranty. If they won't, perhaps you could pay a more full-service shop to do it. And I was suggesting putting another wheel on your bike. But either test would be helpful. Both tests would be most conclusive.


Clean drivetrain? Hmm that's something I want to do this weekend. cleaning the chain is fairly easy, but I have trouble getting to all the grit in the front gears (there a better name for it?) and stuff, do you have to take it apart? Or OK if I were to hose lightly and toothbrush or something? The ones in the front are called chainrings, the ones in the back are called cogs. Don't worry too much about the buzzwords; there isn't a quiz at the end. I've discovered a great tool for de-gunking and de-greasing. Take an old drinking water bottle (Poland Spring or the like) with a "squirt" top. Fill it with Citra-solv or your favorite citrus degreaser (we buy Citra-solv by the gallon 'cuz it's so useful in general cleaning as well). When you pull the sqeeze top thingy just partway open, and squeeze on the bottle, it comes out in a kind of spray. Anyway, a treatment like that, and a toothbrush (or even a rag folded over) does a pretty durn good job cleaning between chainrings/cogs, without having to take anything apart. For really tight spots, a bunch of Q-tips work well too.

Y'know, it just occurred to me, it's still possible it's a cable problem. Maybe there's restriction in the cable movement, but only around the position it happens to be in when the shifter moves from 5 to 6. Look at the length of the cable. Most likely, there's shroud coming right off the shifter, which ends at a stop somewhere near the top/front of the frame. Then it's open cable for a while, followed by a shrouded section leading up to the derailleur. Look at the places where the open cable goes into the shroud, including where it comes out and attaches to the derailleur. Slowly shift the shifter between 5 and 6, and look very closely at each point, and see if there's a slight kink, or any hesitation in movement of the cable.

No damaged teeth, derailler not bent and adjusted correctly,all clean and Lubed. Bet its the cables. Clean and lube the cables. Failing that it could still a lot of other points that are causing the problem. Main one I have come across is wear in the changers, and there's not much you can do about this, except get new ones. I find that Cables only last me about 6 months max, and changers start causing double click problems from quite early on. Hopefully my new LX ones, The 3rd set of changers in 4 years, will last longer.