Chain slip

damocles10

OK so everything mechanical seems to go wrong at the same time - to be expected sometimes.

Last week I nearly came a cropper as my chain slipped twice while pulling away from traffic lights, first time totally not expecting it and ended up nearly over the bars and going 90 degrees in to traffic [Not Good!!!], luckily drivers were sympathetic and asked if I was OK - nice, they're not all bad.

Second time, a bit more cautious, it slipped and I ended up on the crossbar, missing the essentials luckily

Normal troubleshoot - look for wear on chain and cassette, chain - Campag 10 speed had .25 wear - that's a little worn but OK and the cassette perhaps 5 months old ( equates to around 3k miles - I crashed badly last summer and still recovering otherwise it would be more ). Usual remedy new chain and cassette, no joy....the chain is still slipping and not engaging the cogs. It is fine once engaged and the gears shift OK, it's only when I stop and the chain need at least a half rotation to lock on.

Any ideas what is going. Could it be the rear derailleur - this may have been damaged during the crash and the symptoms are only now starting to surface.

Any advice would be greatly appreciated.

Chris

dgunthor

sounds like it may be the freehub of the wheel - the cassette should rotate backwards freely but 'engage' when you pedal forwards. if it's worn then it may not be engaging properly when you pedal after a stop.

try getting off the bike and pedalling the bike by hand forwards and backwards with the rear wheel off the ground - is it engaging and turning the wheel each time you pedal forward or hesitating? if so easy option is new rear wheel, cheaper option is new freehub for the wheel.

HTH

damocles10

Thanks dgunthor, the freehub body does have nicks and grooves where the cassette has dug in to the metal ( 6 years old ) I wonder if this allows the cassette to move slightly. The pawls and free hub connection to the wheel looks fine - I do grease and check the pawls every year as I do not like the clicking noise.

Checking the chain rotation off the bike and by hand doesn't reveal anything untoward. It seems to happen when there is a bit of torque going through the drivetrain. I have seen this with a worn chain/cassette but as I have replaced the chain and cassette ( while I cannot rule new parts out - some need some miles to wear together ) I would expect the issue to be lessened or resolved, but it is still happening.

dee4life2005

Is the rear derailleur taking up the chain slack properly? If not that could probably cause it, and a good clean usually sorts it - I had that exact problem recently.

damocles10

Thanks dee4life2005, I will give the rear derailleur a good clean tomorrow, when I back pedal there is slight catching on the chain. Thanks for that tip!!!


Chris

damocles10

Amazing, gave the derailleur a good clean and it's fine. The gunk around the jockey wheels was so think and gritty. Thanks dee4life2005 it must have been a chain slack issue not allowing the chain to engage the cassette.

I guess with all this bad weather, all the dirt builds up quicker.

Chris

damocles10

Started happening again today.

Free hub pawls are not engaging wheel therefore there is slipping - Is the wheel for the heep, 6 year old Zipp 404.

I have cleaned it but one pawl seems a little sluggish to spring back. The teeth in the wheel to engage the pawls look a little worn but not too bad - I do not know what the wear threshold is.

Chris