chain "jumps" on rear derailleur

gopher38

Hello all,

Looking for some help repairing my bike. Not sure if I can even give enough information for someone to help me, even if they wanted, but I'll try.

I have a mountain bike that I bought several years ago and ride probably 2 times per week, but mostly on roads. It was pretty low end when I bought it, so the components are probably not the best (actually, now that I look, the rear deraileur is a Shimano Altus), but it's been fine for my purposes for several years. Recently though, the chain "jumps" when I put too much pressure on it, like when I'm starting out or when I'm climbing a hill. It doesn't actually change gears, but it sort of spins freely for about a quarter or a half of a crank turn, and then recatches. It can do that several times though, which is really annoying if you're trying to climb a hill. I brought it into a local bike shop a couple of times, and they adjusted it, but the problem comes back soon after. They don't charge much, but it is $20 or so everytime I go in there, and even though I've never done much on my bike beyond change the brakes, I do like to mess around with tools and since I'm recently unemployed and have the time, I figured, what the heck, maybe I'll try to figure this out myself.

Anyway, I think that the problem is on the rear derailleur. I did some looking on other web sites, and the derailleur seems to be fairly well lined up with the cogs on the inner and outer chainrings. (i.e when I shift all the way up, the derailleur is in line with the outer chain ring; and it's in line with inner when I shift all the way down). I think that it's trying to shift when I put too much pressure on it, but I'm not even sure which way it's trying to go, because, like I said, it spins free for a split second before grabbing again. I'm hoping that somebody knows off the top of his head which way it is trying to go, and then I can use the adjustment screws on the derailleur to find the right position for it.

Anyway, if anyone has had a similar problem, thanks for any guidance.

Regards.

nicklouse

either the caseette is wornout on the teeth or the freebody/hub and gone and needs replacing.

but have a read of the gears section of parktools.

stumpyjon

Chain's probably stretched too , infact that's probably the first thing to change. A stretched chain doesn't fit the sprockets as well, so instead of smoothly engaging, the rollers in the chain can hang up on the teeth of the sprockets, this most often happens when you are putting a lot of pressure on the chain as it is obviously at it's most stretched. I've had to change my chain and cassette recently, it's quite a common maintenance tasks. A lot of people don't realise that chains and sprockets wear out, they usually put up with poor shifting for years. You usually need to change both cassette and chain at the same time as they wear together.

Unless I've misunderstood, adjusting the srews on the rear mech won't make any difference, these screws control the maximum movement of the rear mech, they are effectively end stops to prevent the chain shifting off the smallest sprocket or worse off the largest sprocket into your spokes. To change the indexing of the mech you need to alter the tension on the cable which depending on the type of mech and shifters you have is achieved by turning the barrel adjuster (where the cable exits the mech / shifter). If the barrel adjusters are srewed out, screw them back in ad shorten the cable at the mech end by loosening the retaining bolt and physically puuling more cable through. Fine tune with the barrel adjusters (cables stretch as well).

stubs

I am afraid you are going to have to buy a complete new drive train, chain, cassette ,chain rings .

If you carry on using the bike with a skipping chain you are going to end up walking home one day and it will be even more expensive. I do about 4000 miles a year and I replace everything at least once a year but then I am totally anal about maintenance and cleaning.

A mate who washes his bike once a year wether it needs it or not gets through chains about every 2 months

gopher38

Thanks much for the help. Between these comments and those I've received on another forum, it seems clear that the drive train is the problem. It seems silly now, but it never occurred to me that the chain could slip over the sprockets. I assumed that the chain was jumping up and down the chain rings - east and west, so to speak. There is quite a bit of give in the chain, and while the chain rings aren't "pointy", there is visible wear. I'm sure that the chain is sliding north and south. I live in the Grenoble area, so I spend a lot of time powering up hills (well, "powering" for me that is). That probably causes the chain to wear faster also. I wish I'd known this sooner, because I've been having trouble in the hills for months, usually being forced to put it in an overly low gear and spin to avoid the skipping.

I'll go to the bike store tomorrow and probably replace everything, as you suggest. Next time I'll know to keep a closer watch on the chain.

Thanks for the tip on the Parktools site also. Very thorough.

big_southern_jesse

I've just had a similar problem.

When pedalling I could feel the cranks suddenly spin easily forward under my feet, so knew I was losing drive somewhere. With a quick chat to a few people, it was pretty certain to be the freehub, as nicklouse suggested. THis is because it was such a quiet and smooth slip. For the cranks to slip forward that farif it were the chain slipping, it would mean pulling a lot of chain over the cassette, likely to make a noise and to feel rough on the pedals.

The freehub is the ratchet inside the cassette, if this is slipping due to wear or crap in there, then it's likely to be this smooth silent slip.

I couldn't get a replacement for mine, so stripped the entire thing, cleaned it, and put it back together. Not only did I have no bits left over at the end( ), but it now works well.

Of course, this is what happened in my case. It's only a suggestion as to the difficulty you are having...

Hope it sorts itself out anyway.

Also, everybody I talked to, or read up on, said that freehubs weren't worth servicing yourself. I only did it because replacements went out of production several years ago, and at this time of year I'm brassic due to Christmas, tax returns and virtually my entire family's birthdays, so couldn't buy a whole new wheel.

Gussio

stubs wrote:

I am afraid you are going to have to buy a complete new drive train, chain, cassette ,chain rings .

If you carry on using the bike with a skipping chain you are going to end up walking home one day and it will be even more expensive. I do about 4000 miles a year and I replace everything at least once a year but then I am totally anal about maintenance and cleaning.

A mate who washes his bike once a year wether it needs it or not gets through chains about every 2 months

Might well get away with just changing chain and cassette, but retaining chain rings.

365punter

i've just noticed the same problem on my bike too. my middle and outer chainrings are very worn (teeth are either very sharp and pointy or they are very short) and a few rings on the cassette are heavily worn too.

the bike's done a bit over 1500 miles now and gets used in all weathers. is this the price of not religously cleaning the drivetrain after every ride?

stumpyjon

Nope, I do clean my drive chain after every ride and only got about 500 miles out of the chain and rear cassette, if I'd spotted the chain stretch earlier I might have made the cassette last longer. It's more down to your riding style and local conditions. For me there are hills everywhere and I do have a habit of mashing my gears which I'm trying to break.

Bought a much more expensive chain and sprockets to see if they will last longer.

gopher38

Well, I went out today and bought a new chain, chainrings and cassette, along with the tools that the store said I would need. First step was to pull off the chain. At first, I thought that I had bought the wrong kind of chain. I lined them up together to get the old length and determine how many links I had to remove from the new chain, but I noticed that they didn't match well. I thought that maybe the individual chain links had different lengths, but in checking the web, I see that they are always 1/2 inch. The old chain now extends beyond the new one by about a link and a half over the length of the chain, which means it's something like 2% longer. Doesn't sound like much, but I'm sure that that can do damage over time.

I'm now a bit worried that I might have to replace the big chain rings near the pedals (sorry, don't know the name). That seems more difficult however and they don't look as worn, so I think I'll replace what I have and see if that fixes it. Regards.

gopher38

Just wanted to say thanks to the posters. I feel like I have a new bike.

Last thing, in case there's a neophyte like me that stumbles upon this thread and does the same thing. Only somewhat tricky thing that I encountered was during the replacement of the chain. The link where I had joined the ends was incredibly stiff and was causing major problems when it passed through the gears. I was trying to loosen it with oil and working it back and forth, but with minor success. Then I read a little note on a site where they said, if you have this problem, you should push the pin in just a fraction more, but using the second slot on the chain removal tool, which pushes the inner plate but not the outer (I believe) and removes the pinching. Sure enough, a fraction of a turn later, link was moving fine.

I'll be replacing my chain regularly from now on. Thanks again.

ginge7289

have not read all the comments but from what you say, i would say the cassette has had it, which means the chain will have to be changed as well. if you really wanna continue riding i would get the local shop to have a look at your chainset to make sure that has not seen the end of its life. sorry gonna cost you a few bucks i think.

stumpyjon

2% stetch on a chain is a huge amount, 0.75% stretch is borderline, 1% is bin it time. Glad you've got it sorted (nice to hear you figured the stiff link thig by yourself).

wetherbob

Yup I have some 'chain jumping' accidents. like when I'm going full-out up a hill, the chain slips and a smash my knee into the handlebars. However i cannot be bothered to fix it - I've STILL got a useless 'Silverfox' (Argos-style) and I've been denying the fact that it will take ages to save up for a new bike.

Just thought you'd like to know.