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Chain Slips/Skips
#1
Trek 470 road bike, yes it's old but well maintained although the chain skips at varying degrees of intensity. I have about 40k miles on this bike and to combat this skip I've recently had the following done by a reputable bike repair shop at the same time: replaced chain, replaced both front rings and replaced the entire cassette.

Skip has improved if such a thing is possible however, it does continue to skip while in either ring and in any gear.

I live in Florida therefore, no hills only flat surface.

What is the next logical thing that should probably be replaced?
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#2
If this is really a cassette bike, it could be the ratchet in the freehub. (If it's a freewheel, then that would have been changed when they replaced the rear gear cluster.)

One other thing I can think of is if it is a shifting adjustment issue. Or it could be a stiff link in the chain.

"Skipping" can mean different things to different people. It's important to know what you mean. Does it jump between gears, does the chain ride up over the top of the teeth and then grab again in the same gear, does the "skip" happen just every 2-3 rotations of the pedals?

Finally, make sure they put on a compatible chain. If they put an 8-9-10 speed chain on a 7 or lower speed bike, that could cause problems also.
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#3
(05-14-2014, 06:56 PM)DaveM Wrote:  If this is really a cassette bike, it could be the ratchet in the freehub. (If it's a freewheel, then that would have been changed when they replaced the rear gear cluster.)

One other thing I can think of is if it is a shifting adjustment issue. Or it could be a stiff link in the chain.

"Skipping" can mean different things to different people. It's important to know what you mean. Does it jump between gears, does the chain ride up over the top of the teeth and then grab again in the same gear, does the "skip" happen just every 2-3 rotations of the pedals?

Finally, make sure they put on a compatible chain. If they put an 8-9-10 speed chain on a 7 or lower speed bike, that could cause problems also.

Hi Dave M, Thanks for your response. This is a touring bike from 1995 with two front chain rings (one larger than the other). There are 7 speeds available with each ring. I've included a pic of the type of cassette I mentioned.

This is NOT a shifting issue whatsoever. Chain does not ride above the rings, it does not jump between gears. Skip occurs for the most part under a load but only infrequently. It is not a chain issue as I've had the chain changed a half a dozen times since this issue started.

This freehub ratchet you mentioned... if they changed it they did not charge me unless it's part of the cassette cost. The bike shop did not make the swap out decision, I told them specifically what to change.

I'm thinking bearings somewhere (I suspect there must be bearings that allow the pedal crank to turn).

Thanks again for your help. Please feel free to reply.
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#4
Well, from what you describe...If the pedals suddenly give way under load and then re-catch, most likely I would say that your freehub is slipping. This is the ratcheting mechanism that lets the pedals spin freely one way, but put your pedaling force into the wheel the other. They definitely wouldn't have changed this unless you asked. They don't fail often, but do on occasion. Sometimes flushing them with lubricant helps if it is just sticky pawls inside the ratchet. But you may have to get a new "freehub body".

Yes, there are bearings that allow the cranks/pedals to turn as well as ones on the wheels. IF they were really bad, they could make a lot of noise or even bind up. But they wouldn't make the pedals slip.

http://sheldonbrown.com/k7.html
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#5
(05-14-2014, 09:19 PM)DaveM Wrote:  Well, from what you describe...If the pedals suddenly give way under load and then re-catch, most likely I would say that your freehub is slipping. This is the ratcheting mechanism that lets the pedals spin freely one way, but put your pedaling force into the wheel the other. They definitely wouldn't have changed this unless you asked. They don't fail often, but do on occasion. Sometimes flushing them with lubricant helps if it is just sticky pawls inside the ratchet. But you may have to get a new "freehub body".

Yes, there are bearings that allow the cranks/pedals to turn as well as ones on the wheels. IF they were really bad, they could make a lot of noise or even bind up. But they wouldn't make the pedals slip.

http://sheldonbrown.com/k7.html

Thanks for your reply and patience. I will discuss the potential of a freehub issue with the bike shop. I've attached an image of the bike.
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#6
According to BikePedia; it has a seven speed cassette on a Shimano hub.
http://www.bikepedia.com/quickbike/BikeSpecs.aspx?Year=1995&Brand=Trek&Model=470&Type=bike

40K miles is a lot to expect from a freehub. A Shimano freehub should not be hard to replace.
http://www.amazon.com/Shimano-STX-RC-Acera-X-7-Speed-Freehub/dp/B001GSKU0U

After you take the rear wheel off the bike; remove the cassette (special tools required); then the rear axle, and the freehub needs a 10mm Allen (hex) tool to remove the bolt holding it in place. Remove the bolt, pull off the old freehub, install new, replace bolt, axle etc.
Nigel
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#7
(05-14-2014, 09:19 PM)DaveM Wrote:  Well, from what you describe...If the pedals suddenly give way under load and then re-catch, most likely I would say that your freehub is slipping. This is the ratcheting mechanism that lets the pedals spin freely one way, but put your pedaling force into the wheel the other. They definitely wouldn't have changed this unless you asked. They don't fail often, but do on occasion. Sometimes flushing them with lubricant helps if it is just sticky pawls inside the ratchet. But you may have to get a new "freehub body".

Yes, there are bearings that allow the cranks/pedals to turn as well as ones on the wheels. IF they were really bad, they could make a lot of noise or even bind up. But they wouldn't make the pedals slip.

http://sheldonbrown.com/k7.html

Hi,

Recently, in addition to what I've previously described the following has been occurring typically at least once during a ride of varying duration. A somewhat loud momentary clacking/clicking noise while the bike is moving forward without pedaling. There is no chain slippage during this event. It seems to me that based on what you've said previously this experience lends to the freehub issue...
  Reply


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