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Chain slippage
#1
I'm riding an old Specialized Crossroads for fitness. Love this old bike but am having gear slippage problems. The bike always had a crisp, no-lag change of gears. About a month ago, shifting mid-range gears got clunky. When I say clunky, I mean a lag before the gears changed and then clunked into gear. Nothing crisp or positive about it. My local bike shop adjusted things & cleaned/lubed the drivetrain, which made things better for awhile. Then the clunkiness returned. Local bike shop then put on a new chain and rear cassette, which again made things better for awhile. But now, changing gears has become kind of iffy. For example, if I'm cruising along in mid-range 7 and downshift to 6, it feels like it actually drops down to 5 for a turn or 2 of the crank, then shifts into 6. Sometimes it takes several turns of the crank and the chain will actually slip before it grabs the selected gear. To be clear, I'm not power pedaling up steep hills or anything when any of this happens.

I've checked out the Repairs section and read thru 'How to Adjust Your Rear Derailleur' a couple of times. But to be honest, I don't know that's where the problem lies. When it comes to mechanicals, I try to take a "First, do no harm" approach. So I'm reluctant to just start turning adjustment screws without some kind of reference point. If any of this is something that you've worked thru to resolve, I welcome any assistance/suggestions. Thanks in advance.
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#2
I had some time to take a closer look @ my bike's derailleur & gears this a.m. Pix below show gouges just below the teeth in three of the inner rings. These are not the same pix. There are two (2) sets of gouges that are approximately 180 degrees apart on the cassettes. At first, I couldn't believe it. The yellow stuff on the gear teeth is where I used a marking crayon to indicate where each set of gouges started. Looks seriously wrong to me.

   

   
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#3
(08-30-2020, 02:37 PM)Bobbo Wrote:  I had some time to take a closer look @ my bike's derailleur & gears this a.m. Pix below show gouges just below the teeth in three of the inner rings. These are not the same pix. There are two (2) sets of gouges that are approximately 180 degrees apart on the cassettes. At first, I couldn't believe it. The yellow stuff on the gear teeth is where I used a marking crayon to indicate where each set of gouges started. Looks seriously wrong to me.

Hi Bobbo,

I think your initial problem, before making the changes, was related more specifically to the rear derailleur than to the chain or cassette (hard to say without seeing the original parts). I would have taken the rear derailleur off the bike and fully disassembled it in order clean, lube, and rebuild. Cleaning/lubing the cassette, front rings, and chain should be done at the same time to eliminate those variables from being part of the problem. I doubt that the cassette was worn out; the shop should have shown you the difference between your old one and a new one indicating what was worn out and why it needed replacement (I doubt there would have been much wear to show on the cassette, maybe one or two gears, but not the entire cassette). Always ask to see the old parts for any repairs (bike, auto, etc.); make sure they are saved until you get to pick up the item in question and it gets tested properly before tossing out what may be perfectly good parts. The same thing goes for the chain. Also, you may want to have the chain width verified for the cassette (7 speed?). A "sticky" rear derailleur can cause many problems, but "delayed shifting" is common with the cage not yet settling at the chosen speed/gear during the actual shift, but "slowly" getting to the proper point on the cassette due to debris and "gunk" built-up over a period of time. Worn out jockey pulleys can also lead to problems, but are a cheap easy fix. The "sticky" derailleur problem can usually be resolved with the previously mentioned overhaul of the part(s); but if there is excessive wear in the pivot points of the mechanism, and/or pulleys it may not fix the problem until the actual part/derailleur is replaced. I regularly use derailleurs (with good pulleys) that are 40-50 years old that shift nearly as well as when new unless excessive wear and/or damage has made them inoperable for regular use.

Those "gouges" on the cassette sprockets are, I believe, "ramps" engineered into the parts in order to assist with moving the chain more efficiently from a smaller sprocket to a larger one. These are common features on "newer" style cassette sprockets and chainrings (which have "ramps" and "pins"). Newer chains do not have pins protruding as much as on older chains so the "odd" features on newer front and rear sprockets are designed to "catch" the chain and allow for smoother/quicker shifting, especially when shifting under a high load (climbing, accelerating, etc.). You may notice differences in the gear teeth themselves which are designed for the same purpose, to aid in the moving of the chain during shifting.

Make sure that the derailleur(s) is/are properly aligned on the sprockets when in a specific gear at your shifters (I assuming you have indexed shifting). If the indexing adjustment is off than you will have shifting issues. The indexing can be adjusted at 1 or more places depending on the actual bike/parts configuration; adjust at shifter, frame cable stop, and/or at the derailleur).

I am curious as to the age of the bike, and about how many miles are on it. I know Specialized has made that model for about 25 years so it's hard to determine age when only told that it's an "old" bike ("old" is 2 years to some, and 20 years to others).

Make sure that the shop mechanics have taken it for a "test ride" (specifically ask them), and always go for a test ride before leaving the shop (I'll sometimes test ride for 10-15 miles depending on the work done; even (and if I did the work myself). Also, when things seemed better for "awhile"; how long was that in riding time/distance (2 days, 2 weeks, 20 miles, etc.)? If new parts were the solution, then you shouldn't have issues unless something had gotten out of adjustment because the new parts haven't worn out that quickly. Ask what specific work was done to service the rear derailleur: was it a basic cleaning, or was it completely dismantled and overhauled?
Take care,
Jesper

"I am become Death, the destroyer of bicycles." NJS
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