Chain slip?

[nuyorican]

That's the best way I can think to describe it.

I recently put my old mountain bike back in to service after crashing my road bike and bending the frame. It's hard to say what's going on exactly, but when I put hard downward pressure on the pedal it sometimes kind of 'gives way' and my foot kind of follows through and I nearly come off. Almost like the chain slips.

Any ideas what it could be? Too long chain perhaps? Would taking a link out help? New chain? Worn cog teeth?

Thanks

[JEA1K]

nuyorican said:

That's the best way I can think to describe it.

I recently put my old mountain bike back in to service after crashing my road bike and bending the frame. It's hard to say what's going on exactly, but when I put hard downward pressure on the pedal it sometimes kind of 'gives way' and my foot kind of follows through and I nearly come off. Almost like the chain slips.

Any ideas what it could be? Too long chain perhaps? Would taking a link out help? New chain? Worn cog teeth?

Thanks

Could be any of the above. If the bike hasn't been used for ages, is the rear mech cage spring stiff causing the chain to run slack?

[river_rat]

Sounds likely to be a worn out chain, which more than likely means you also need a new cassette at same time.

[dudleybloke]

Is it chain slip or is the ratchet pawl worn out?

[dave123456]

dudleybloke said:

Is it chain slip or is the ratchet pawl worn out?

A muted freewheel noise would suggest pawls.

Put the chain on the largest chainring (I’m guessing it’s not 1x!) and pull the chain towards the front of the bike, if it comes away more than about 5mm your chain is worn.

That’s assuming you don’t have a chain measuring.

[magpie215]

When was the cassette and chain last replaced.....how many miles on it?

[nuyorican]

Thanks guys. I got it up on the stand earlier to have a fiddle with the gears, clean and lube etc.

With regards to when certain components were installed/replaced etc - it’s a bit of a Frankenstein/Trigger’s broom bike. Cobbled together from random components found in mine and mate’s parts bins from memory. As such I’ve no idea…

I used to use it as a general hack until I restored a vintage racer and left this in the shed.

Anyway, I’m going to try that trick to test if the chain is stretched, so thanks for that. The issue usually presents when I’m setting off, especially uphill. It’s quite a dangerous problem as I’m usually putting considerable downward force in the pedal when it happens.

So I’m now tinkering with the gears again to see if it’s an indexing issue. It’s been a while since I fettled gears. Can you remind me which screws do what? Lower for spoke side limit, upper for outer limit? What does the other one do. Hard to replicate the issue on the stand as I can’t put pressure on it. I seem to have improved the shifting onto the lowest gear/biggest cog which it was struggling with before. But now it’s skipping a couple in the middle or shifting on it’s own.

[nuyorican]

Also noticed the lower jockey wheel is almost smooth. Would that have an impact?

[dave123456]

The other one is the b tension screw. Which appears ok on the photo.

If you’re feeling fussy the outer chainring needs rotating 90 degrees anti clockwise so the little tab sits behind the crank arm.

If you shift into the smallest cog on the cassette and then shift down one click, turn the barrel adjuster on the rear derailleur anti clockwise until the chain just starts to catch the third cog. Then clockwise quarter turn. That should index the gears assuming you have the other two limit screws set right.

[dave123456]

nuyorican said:

Also noticed the lower jockey wheel is almost smooth. Would that have an impact?

Doubt it but it needs replacing

[nuyorican]

dave123456 said:

The other one is the b tension screw. Which appears ok on the photo.

If you’re feeling fussy the outer chainring needs rotating 90 degrees anti clockwise so the little tab sits behind the crank arm.

If you shift into the smallest cog on the cassette and then shift down one click, turn the barrel adjuster on the rear derailleur anti clockwise until the chain just starts to catch the third cog. Then clockwise quarter turn. That should index the gears assuming you have the other two limit screws set right.

Well I’ve just been for a short test ride and all seems good. Maybe I fluked it with my fettling. I’ll follow your instructions if it returns. Seems happier though.

Thanks again.

[JagYouAre]

I would also say it looks like it could do with a thorough degrease, clean up and re-lube.

It might not fix the main issue but can definitely have an impact on clean shifting.

[nuyorican]

Now noticed the pedals wobble up and down in their spindles. Like the bearing races have come loose. I may well just replace these though. Can’t work out how to take them apart.

[nuyorican]

JagYouAre said:

I would also say it looks like it could do with a thorough degrease, clean up and re-lube.

It might not fix the main issue but can definitely have an impact on clean shifting.

Absolutely. Given it a cursory clean up whilst I’ve been working on it. Definitely improved matters, if only to get the blank gunk out of the way so I can see what’s what.

[Floor Tom]

nuyorican said:

Also noticed the lower jockey wheel is almost smooth. Would that have an impact?

Not a huge problem by itself, but it would suggest that the bike has been quite a bit of use and therefore it's not unlikely that the chain and cassette are worn.

I would swing past a bike shop and ask them to put a chain wear gauge on the chain, see how bad it is.

[Camoradi]

I had a similar problem on a bike which jumped on two gears, oddly in the middle of the cassette.

After I had replaced everything else, it turned out to be the rear derailleur hanger wasn't straight. Replaced that and the problem was fixed.

[stargazer30]

well it could be...

Worn chain
Worn cassette
Knackered freehub
gear indexing out (including b screw) and it skips up or down on load
bent rear mech hanger
kanckered rear mech spring

or a combination of the above. So you need to check and rule out each or take it to a bike shop.