Help please - Chain slipping badly when applying pressure

First thing is to STOP.
Stop adjusting this, buying that, fettling with the other. It's got to the point where any of the above answers could be right or wrong and you have no way of telling which is which or the expertise of the people offering their opinions based on a few photos and a vague description.

You're just throwing money at the problem and hoping it'll go away.

Take the bike to a reputable shop. The problem could be anything from half a turn on the barrel adjuster to an entire new drivetrain and the only way to find out if you're not sure what you're doing is to hand it over to the people who do know.
If you don't trust the opinion of the first shop, take it to a second, there's no harm in asking around - go in and say "could you have a look at this issue and tell me what you think is causing it?" rather than simply "fix this". That way you're under no obligation to get any work done, you can evaluate the info the shop has given you and go from there.

Posting on here is just going to lead to a host of "experts" confusing matters still further and you buying various random bits of drivetrain piece by piece (any or all of which may have varying degrees of compatibility issues with each other).

looking at the view from the back the derailleur looks canted from the picture from the side it shows damage if this damage occurred on that bike then there is a fair chance the hanger is bent with a worn chain and cassette no slipping but new chain new cassette slipping. so LBS for them to check the hanger is straight

Haggisbasher wrote:

I have a day off tomorrow so I will strip it down, recheck chain length and derailliuer.

Your original posting and subsequent comments suggest that everything works fine on all sprockets and the big chainring.

You’ve said that the only time the skipping happens is when you use the inner chainring. So the problem could also be related to the inner chainring.

There’s a discussion on here under "Chain and Sprocket Wear" with some pictures of combinations of new/worn chain on new/worn sprockets that might help you decide whether your inner chainring is worn out or not by inspecting it with the chain on it.

I had something akin to this on my defy. The dérailleur had got stiff and so wasn't tensioning the chain properly. A bit of WD40 fixed it!

Funny, I was just going to say the exact same thing as Stratman, it happened to me just yesterday and WD-40 fixed it for me too.

you haven't made it clear what you mean by the chain "slipping"

Two ways of explaining it are "jumping" - where the chain momentary or half changes to a different sprocket and "disengauging" when the chain and sprockets remain in firm contact but power is not transferred

If it is "jumping" then there is something wrong with the way the derrailuers are set up
If it is "disengauging" then there is possibly a problem with the hub - although I've never seen anything like that

some of the words we use for bike transmission aren't the best (like "chain stretch" for example) and "slipping" covers at least two different things

If that's a short cage mech how big is that cassette?

As you may have exceed the capacity of the mech explaining why you are not getting the largest sprocket.

I would also TAKE IT TO THE BIKE SHOP.

A good one.

I have been having the exact same problem with my bike chain recently! When I replaced the rusty old chain and matched the length of it with the new one, the chain doesnt grip in and hops on the same cassette when I thrust (standing up while cycling/ picking up speed). Is the cassette the only reason you think?

Ancient thread I know but if (like me) someone stumbles upon it, I had this problem on a just purchased second-hand bike where the inner chain ring was the wrong way round. The teeth are not symmetrical and the chain can ride up and over the bevel when the ring is flipped.

It wasn't obvious to me even when I was looking for it. But if you run a straight edge from the centre to the teeth you can see it clearly. Any markings on the (inner) ring should face towards the bike.

Chains snap because they have been installed incorrectly.
They don't snap because they get worn, and certainly not because they've done 2'000 miles!

Chains, chainrings and cassettes wear together. Wear them out; you'll be surprised how many miles you get out of them.

All these problems stemmed from measuring the chain and following received wisdom regarding what to do.

Chain checking is a modern phenomenon; no one did until 3 or 4 years ago.

Run chains and cassettes together, throw them both away when they eventually die; you'll get a far easier life, far better shifting and save money.

I see you have aftermarket jockey wheels (red). Could these be a contributing factor I wonder? Is it a Shimano/Sram chain? Would be interested to see the position of the derailleur with the chain on the small chainring at the front and smallest cog on the cassette.

It is worth getting a chain measuring tool and using it every time you clean your chain, and not letting the chain elongate beyond 0.75. After 0.75 everything starts to get expensive as the chain very quickly eats its way through your cassette sprockets and then eventually the chainrings.

If your chain has reached 1.0 on a chain measuring tool (i.e. worn out), your cassette is probably worn out also.

A worn-out chain will very quickly wear out a new cassette. Your new cassette might have fallen victim to this chain already?

I’ve managed to wear out a Shimano Deore alloy 36T middle chainring such that the chain slipped. Replaced it with a steel one and don’t let my chain get that worn anymore.

My experience is that by changing chains regularly I can get my cassettes to last around 3x longer than my chains.

Some people recommend having 3 chains and rotating between them on the same cassette so that everything wears at approximately the same rate.

Time to treat yourself to a new bike? But seriously, lots of good ideas here and do let us all know when you figure out what the problem is. Best of luck.

Does the derailleur move freely fore and aft? If it is at all sticky that might be the cause of your problem. As previous posters state, if the cassette isn't worn then the problem could be chain tension. Does the chain sag when you use the gear combinations that slip? Is it difficult to back pedal using the slipping combinations? Either of these scenarios indicate a chain tension problem that could be related to chain length or a derailleur that sticks in certain places. If this is the case it would explain why you can pedal without trouble on the big ring but the small ring to small sprocket combinations slip because there is less tension in the chain. If your rear mech is sticky give it a good clean and lube all moving parts.

Could it be the chain length? Silly question in a way. But I bought a chain from Cycle Surgery and was told that it was the right length and I just needed to attach it with a power link. I thought that was unusual. Rode the bike home and the chain slipped all the way - initially thought it was a worn cassette, but after a bit more inspection I realised that the chain was entirely too long.

I was furious at the CS, but also myself at taking the utter rot that they told me as red. I did have an accident, and consider myself fortunate that it didn't happen on a road with cars.

Can you provide a photo that is taken side on to show the whole drive-train?

From that picture it is really hard to tell, but the hanger does look off, as the top jockey wheel looks to be at an angle to the chain as it runs onto the cassette. Also it may be the angle of the photo, but the main mech body appears to be pulled right back, and with that amount of slack in the chain a conventional mech wouldn't sit like that. Is it stuck in the rearward position?
My guess is you pulled it back to get the wheel out, and it has got stuck in that position.

It's hard to tell much from a single picture. Though I also think the derailleur pulleys don't look adjusted inline with the cogs - possibly a bit too far to the right. Also something maybe be funny about the barrel adjuster; I can't see the lip of the inner metal bit, is it just fully wound in? And the ferule on the end of the cable doesn't look like it is sitting straight in the adjuster. However it's probably all just the light!

Was the new chain shortened to the same length as the old one? If it was and there were no problems before, I'd then assume the problem is something else. If the chain doesn't sag or rub back against itself with the small chainring and small cog it's probably not the issue, though it may be worth sizing the length properly.

I would consider finding a bike shop with a good workshop if you are stumped. Paying someone with the experience and who can see the bike first hand may work out cheaper than throwing new parts at it when the old parts might actually be fine.

When I replaced the chain and cassette on a mountain bike a while back, the wear on the middle ring was enough to cause slipping when I put the power down. The chain slipped on the chainring but it was hard to tell where the slip was happening. Replacing the chainring eliminated it. Hope it will for you too.

However, as others have said, the angle of the rear mech looks weird - the body of the mech seems to be rotated back and up from its normal position. Can you take a photo from the side of the bike in the same gear?

The chain routing through the rear mech also looks funny but it may just be the perspective and the odd angle of the cage. Again, photo from the side and we'll be able to tell if all is well.