Chain Slipping – can anyone offer any other suggestions to my problem?

I know the drive train is a complex area with many variables, but can anyone offer any other suggestions to my problem? I recently changed my rear cassette and chain (Shimano CS HG50-9 and SRAM PC951 Chain) and now the chain won’t stop slipping. I’ve tried many times to adjust the tension of the gear cable but when it appears fixed, it starts jumping on a different couple of sprockets. I thought I’d read somewhere that HG cassettes were particularly narrow so should I have bought a HG chain? Is the sram one too wide?

I don’t think the rear mech (105) is bent (no reason it would be), but then I wouldn’t know unless it was major. The chain length seems ok. When not on the bike it all seems to work fine but then under pressure is when the problems start – usually when pulling away from the lights trying to get ahead of traffic.

I’m quite a competent bike DIY’er and have set up/replaced gears, cassettes and chains lots of times, but this is just becoming a pain in the butt! Just so frustrating I don’t want to stand on the pedals for fear of it slipping as it’s put me in a couple of unwanted situations in the last few days.

you could try spinning the derailleur round anti clockwise (i think), just a bit. this can enable more of the chain to be on the cogs.

Are the links in the mech stiff? i.e. is it moving so that the chain is getting enough wrap around the gears (especially in the smaller cogs)?

Does it happen in any particular gears?

The mech is probably fine, i’d be having a look at the mech hanger. From your description it sounds like the bike is your commuter so some other friendlt commuter may have bashed your rear mech by accident when you had your bike locked up if you can not think of any reason it would be out of alignment from your use.

Sounds more like it’s the freewheel that’s slipping to me.

Have you still got the old cassette and chain? If so refit that and see what the affect is. Still an issue or not?

I have recently done similar and found the issue to be with the chainset. So it may be that the old chain was meshing well with the chainset as it was equally worn but now the new chain just does not fit.

The wax that some chains come covered in is not a lube. In fact it can sometimes cause skipping. Wipe it off and lube it properly. And change your middle chainring.

I had this exact problem this weekend after fitting a new cassette and chain – after much headscratching and thinking the freehub had gone or that it was a dodgy cassette or chain, it was simply that the (middle) chainring was worn. Put a reasonably new chainring on and all was fixed!

Thanks for replies thus far, in response to some of these:

oxym0r0n – Doesn’t happen in particular gears, randomly can be any. Mech not stiff

Rusty Mac – Bike is not left locked up so unlikely to be bashed

boriselbrus – Could be the freewheel, i whip that off and have a look, sounds clean though

Mark N – still got the old cassette and chain, was pretty much the same reason for replacing it in the first place

BigJohn – Have lubed, but didn’t clean it first, will try.

orena45 – This is possible, the old chain and cassette was pretty worn out and the chain did come off yesterday, i only have two front chainrings so the smaller does get a lot of use, but it does feel like it’s happening at the rear.

but it does feel like it’s happening at the rear.

How can you tell? From what you’ve written it sounds very much like a worn chainring. They get deformed by an old chain and will not grip a new one.

simbob – likewise, mine felt like it was coming from the rear hence why I faffed with trying different cassettes and taking the freehub off to inspect it. Would definately recommend trying a new chainring.

I had this on a bike – took ages to find reason. In the end i found a small crack by the bottom bracket on the down tube which allowed the frame to flex more under pressure ie when starting off out the saddle due to the rear mech cable being pulled with frame flex causing the mech to miss align

agree, via personal experience, about it probably being a worn front if chain/rear new, as I had same issue, it’s really hard to work it out whilst cycling though

other tip, turn bike upside down and slowly roll wheel whilst inspecting/feeling chain to make sure all pins in/no bends etc, I had an issue where a pin was partly out and when it occasionally clipped something it jumped the chain

Recon it’s your front chainring. I always try to skimp on it when changing the chain and freewheel. I went through the process last weekend. Exactly the same slip under peddle pressure. New chainring sorted it. The front chainring never looks too worn until you compare it to a new one!
Also worth changing the lower jocky wheel on your rear mech if you haven’t already.

Would definately recommend trying a new chainring

Right i’ll get one today! Thanks all.