andrew61987

Hello, new here but as I am starting UC Davis in the fall I see lots of posting in my future (anybody who has been there knows what I'm talking about). I'm an experienced rider but outside of changing tubes I have not done much work with bicycle mechanics. I've rode a GT Pro Series most my life so i'm less familiar with the operation and maintenance of mountain bikes. I do have access to tools and I know how to use them.

I have a Specialized Rockhopper 24 speed that is a few years old. All the parts are original. The problem is very hard to describe, but here goes. Often times I will hear what I would call a "stress clang" that is rather loud and acute. I feel a little slip/shock in the pedals when it happens indicating that something in the drivetrain in slipping. The movement is NOT significant enough to be the chain skipping teeth - the pedals simply don't move nearly that much. I cannot tell if it is originating in the front or the rear.

It only happens when I'm putting maximum torque on my pedals, ie, high gear, low speeds, all my weight on it.

I do not know the specifics of my components so here is a picture.

Any advice on how to diagnose or fix this would be great.

https://i371.photobucket.com/albums/o...7/P1060834.jpg

Dan The Man

Sounds like a stiff link in your chain. How frequent is it? Once every few pedal revolutions? Do you hear your tensioner lift up and drop back down? Go over your chain and see if every link bends freely. If one of them doesn't, lube the crap out of it and flex it side to side to loosen it. If that doesn't work, you might need to use a chain tool.

andrew61987

A lot of info here, sorry...

I just tore the drivetrain apart and degreased all the sprockets and chain and got all the dirt off then re-oiled it. I went over every link on the chain and everything moves perfectly free. I found instructions online for complete derailleur adjustment and tweaked it to the best of my ability. It still does the exact same thing. I do not hear the tensioner move at all for this particular noise. It doesn't clang every revolution, more like every mile, but then again only when I'm torquing on the pedals to accelerate which isn't all the time. I'm able to duplicate it by flipping the bike and repeatedly accelerating the wheel in high gear with my hands then applying the brake to slow it down. If I do this for maybe 20-30 cycles, I will hear it MAYBE once. I can clearly hear the sound emanating from the cassette area.

I'm having two other problems with the bike, maybe they are related:

The chain will skip teeth big time when I'm using the smallest sprocket on the casette (bad enough to injure me because the pedals give while i'm accelerating making me about fall off the bike). It happens about once every 100 yards of using the small sprocket. Perfectly safe to use the next-smallest gear so this is what I've always used. This is different than the above problem which happens in all gears, the actual chain skipping ONLY happens on the smallest cassette sprocket!

Lastly, the teeth of the upper idler sprocket of the rear derailleur will rub the teeth of the largest cassette sprocket when I have the bike in it's lowest overall gear. I found the adjustment for this (the B-screw as I've learned), and maxed it out. Helped some, but the teeth still touch.

When I had the bike upside down I did notice that the cassette has a slight wobble to it while the wheel is coasting. Very slight, you can only see it when looking up close. Could this small wobble cause a big problem?

I feel I should mention that although this bike is a few years old, I estimate that it has no more than 600 - 700 miles on it. I've only used it casually.

Dan The Man

Might be the freewheel rachet slipping, although I haven't heard of it happening like this before, usually you just go to full coasting. If the cassette wobbles, it could be lifting the chain up and then dropping it down, kind of like being between gears. Cassette wobble sounds more like a loose rear wheel bearing to me. That will lead to other problems down the road. All in all, it depends on how much longer you want to ride this bike. If you plan to ride it into the ground and get a new one, probably doesn't matter that much. But if you want to keep it a long time you should look at addressing some of these problems, like chain skip.

andrew61987

The ratchet slipping is what I've thought it was from the start. Occasionally, when the chain sounds like it's skipping, it does act like it's in "neutral" for a second (if there was such a thing on bikes) then it bites.

This is also the only mountain bike I've ever ridden that doesn't click when you coast, it rolls silently, reminiscent of my days on a 20" Huffy with a coaster brake. And I do need this bike to work reliably for a long time to come, as it's about to become my primary method of transportation. Maybe I'll buy a new ratchet mechanism and cassette for the rear and just be done with it?

Dan The Man

skipping teeth probably means your chain has stretched out and started grinding down the teeth. Since the smallest cogs get the most torque, they start skipping first. So if you are going to replace the cassette, you should probably replace the chain, and maybe the chain rings too.

biketowork101

I had a similar problem that ended up being the chain. It would be best anyway for you to replace the chain if you are wanting a reliable commuter bike. Replace it with a compatible Sram (or other brand) chain that has a quick link for easy removal.

What happened with my bike was one of the links had a piece that wasn't milled correctly and was sticking every so often. It was a lot of trouble to pin point the problem. I adjusted the all of the parts that I could, cleaned and oiled the chain on a daily basis, and even disassembled the rear cassette, but the problem kept occurring. In fact, I couldn't find the exact reason until I popped off the sticky link (after several months of jumping, clanking, and everything else, it finally stuck) to slip in a quick link.

Even if you don't think that it is the chain, it might be best just to swap it out for a new one with a quick link. It would help you to eliminate one variable and also give you a new reliable part that can be easily removed for cleaning and re-oiling when needed.