Bicycle Tutor

Hello all,

I'm riding a Specialized Sirrus 2010 hybrid style roadbike. It is an all aluminum frame that I've uprated with various parts for touring.

I recently replaced the cassette that took me cross-country with a shimano 8-speed replacement due to a problem with skipping, predominantly in 2F:4R gear. I was told that this was likely occurring due to cassette wear and since that cassette had seen over 4k in miles I figured it was time for a new one.

Well after having the shop do a thorough inspection and installation less than a month ago I popped my wheel off and put it back on only to get skipping again. This time however it is skipping across most of the gears.

I alleviated the problem somewhat by installing a new 8-speed chain -- I previously had a 9/8 speed chain. It now only skips in the middle gears.

When I took it in for a quick look the mechanic suggested that cables to the rear derailleur had a large amount of resistance which pointed to the derailleur not indexing exactly correctly. He lubed it up and sent me on my way.

The derailleur had been sticking if I let the bike sit for a day but would free up if I tapped it and wouldnt cause indexing problems after that.

As I've said it feels as though the bike indexes the gears properly but will skip out under moderate to high tension. I dont want to skip at a crucial moment because this is now my commuter bike and I've had bad crashes before because chains lost grip.

I read in another thread that perhaps the front chainring is worn and I'll check that tonight -- however how likely is it that the resistance in the derailleur cable is causing this problem? That explanation seemed suspect to me and I'd just like a second opinion.

Regards-
Robert

Hi Robert; Definitely replace the cable and housing.

It's tough to diagnose, but these are two very different problems.

If you have to "tap" the derailleur occasionally to get it to shift right, something is going on. Could be cable/housing or could be the der itself. Also may want to check that the der hanger is not bent. Try detaching the cable and moving the der by hand to see if it moves smoothly and/or has a lot of side to side play in the joints. You can also slide the cable by hand to see how smooth that is.

But if everything is shifting well and it still let's go occasionally under heavy load, that sounds like a chainring, cassette, chain problem. Try to be very specific about what conditions this happens under. Is it in either of the two front chainrings, or only one. Only on specific gears in the back or all. etc. Does it skip worse under heavier load or just randomly skip occasionally.

Possible it could be the freehub giving out, but this is somewhat rare. Also check for stiff link in chain, though unlikely.

The fact that it started up after you removed and reinstalled the wheel points to a shifting/derailleur issue. But sometimes things like this are a coincidence.

good luck

@DaveM

The skipping seems mostly to occur, as I said, in the middle gears. Particularly 2F:4R with occasional skips in all gears lower than 4, and 2 above. Higher gears tend to have no problems whatsoever, however there is skipping on 3 in the chainring in the same ranges as on 2 in the chainring.

The derailleur is stock to the bike, which was in a sliding accident which did bend the hanger, but the mechanics bent it back without issue.

The rear hub is a Phil Wood and was upgraded with new cassette before leaving on my trip (~4500 miles ago). It now has an even newer cassette on.

One of the mechanics on the road indicated that I should remove a link from my chain to improve the shifting issues I had then.

The chainrings are original to the bike.

I saw no wander in the chain in the chain rings when looking down at them, and the chain seemed to rest correctly within the teeth. I could be wrong though.

Uhh, yeah. That doesn't really narrow anything down.
You can try this. Try riding slow, but with your brakes on so you can put a lot of force on the pedals. If you can get it to skip, you may be able to have someone jog along next to you or behind and watch to see where it is skipping. If the chain rides up over the rear cogs, get a new chain and cassette. If it's jumping in the front, chainrings. jumping between gears, maybe new derailleur, cables, etc.

If the derailleur got banged up and it's seizing occasionally now, you probably need a new one regardless. Though I sort of suspect it isn't causing your skipping problem.

Mixing old/new chains and cassettes MAY be the problem. It's usually best to replace the chain at the same time once the cassette's worn. An old chain will wear out a new cassette faster and vice versa.

Finally, keep in the back of your head that it could be a bad freehub. Though they don't typically skip like this, they tend to just fail completely and you can pedal without turning the wheel at all.

Sorry I can't help more than that.

That ralph banged up the RD and bent the hanger narrows it down quite a bit IMHO, Dave. See if you follow me here...
Hangers can be straightend but aren't intended to be. It did its job and saved your frame, Ralph! Replace it. Next time - 99% chance it will snap.
If the hanger attaching bolt (to frame) and Drlr mounting bolt are both tight, do we know the level of skill that the mechanic had? If he did it in a 'Trail-side' fashion, you might get that problem. I've been there several times when the replacement hanger had to be ordered but the customer insisted "I gosta ride!"
More likely though, is Daves thought on the drlr proper being banged up. How bad is the road-rash? If the drlr body is deformed around any of the four pivots, you can get 'stickyness' in a certain area of the drlr's travel.
Try flushing the drlr out very well with high pressure water, a can of WD-40, whatever you have. Debris can lurk in the wierdest of places. Then, use a lightweight oil like TriFlow and lube up every pivot point that you can find. Work that oil in by hand.
Failure to lube drlr pivots is actually one of the most common problems that I seem to address as a bike mech. Well-intentioned people often will sterilize every inch of a bike after a ride and never give a thought to those little pivots. Makes me sad.
And $$.

(Oct 26, 2012 06:31 PM)RobAR Wrote:  That ralph banged up the RD and bent the hanger narrows it down quite a bit IMHO

You're spot on about the derailleur probably being damaged. And I can't tell you how many intractable bike problems I've fixed by dripping a little lube on pivot points and cables. But I'm not sure that points to it being the cause of skipping under load. In my experience, skipping from bad derailleurs or adjustment is worse under light load. When you put a lot of force on the pedals, the chain tends to stay in it's gear better. But skipping under heavy load is classic worn cassette/chain/chainring.

I could be completely wrong of course. But these things are tricky to diagnose in person. Over the interwebs with someone who's not being that detailed about listing symptoms and history is double plus hard.