Bike derailleur adjustment

grizzly1911

I have just replaced9 following failure) the derailleur, chain and droput on my wife's hybrid bike.

It is a basic shimano altus7/8 eight speed unit replaced like for like. The chain was adjusted to match that replaced.

Any hints on adjustment. It works fine when in ano load situation, turned upside down as I don't have a "hanger". I did have to tweak the upper and lower screws slightly to get the derailleur to cover the spread of the gear set.

My wife has tried it but under load (actually being ridden), whilst the shifters move he gears as they should the chain appears to slip on the chain ring. It still holds the gear position.

I probably need to raise the saddle, ride it and tweak as I go but are there any pointers that may help or any obvious checks?

TIA

Strider590

Set it roughly correct with the lever adjusters set half way out, then ride/adjust until perfect. It's also possible that your chain is slightly too long and not under enough tension.

grizzly1911

Strider590 wrote: »

Set it roughly correct with the lever adjusters set half way out, then ride/adjust until perfect. It's also possible that your chain is slightly too long and not under enough tension.

Thanks, a bit of slow mode of transport for you.

The chain was 116 links long a number of reviews suggested it needed shortening to 114. I double checked to the old one and it was 2 links longer. I shortened it accordingly.

There is an adjustment screw from the derallieur which is against the drop out hanger hanger. I guess this may be the one that needs to be used to take out the slack.

thelawnet

http://sheldonbrown.com/derailer-adjustment.html

Or try your local bike shop (NOT Evans/Halfords). £5 or £10 I should think.

Billy-no-Money

If you've changed the chain but NOT the rear cassette (the sprockets), it's possible this is happening due to sprocket wear.

Does it happen in ALL gears or only the ones most often used?
If it only happens in SOME gears then a new cassette might be needed.

As the chain 'stretches' (actually the bushes begin to wear) the rear sprocket wears to match - this doesn't cause any slipping, but a new chain will slip if the sprockets are worn. This only happens under load - just like you've described.


It's not an expensive job, but if you don't have the tools you'll need to get a bike shop to get the old sprockets off.

Norman_Castle

Check the outer cable for damage. Any splits can affect the gearchange.

grizzly1911

Billy-no-Money wrote: »

If you've changed the chain but NOT the rear cassette (the sprockets), it's possible this is happening due to sprocket wear.

Does it happen in ALL gears or only the ones most often used?
If it only happens in SOME gears then a new cassette might be needed.

I will check

As the chain 'stretches' (actually the bushes begin to wear) the rear sprocket wears to match - this doesn't cause any slipping, but a new chain will slip if the sprockets are worn. This only happens under load - just like you've described.


It's not an expensive job, but if you don't have the tools you'll need to get a bike shop to get the old sprockets off.

Thanks good point.

I will have a look at that, if adjustment doesn't fix it.

I brought the special nut (£4 at Chainreaction) to remove the cassette. I needed to do this to replace the wheel guard between the spokes and cassette. I know it wasn't strictly necessary to replace this bit.

The wheel guard shattered when the chain went into it. Not sure whether the dropout broke first or whether it broke because of a chain or derailleur failure, both of which were destroyed. Is was only being used on road.

savepete

The chain slips on the chain ring because the chain may have worn out. Chains extent (get longer) over time and if you combine old and new (i.e. chain and gears) the spacing is no longer the same and they will need replacing.

grizzly1911

Billy No Money and save pete: -

If I do need to change the rear cassette will I need to do the chain wheel (three) or are they likely to suffer less wear due to their greater size and position (puling round rather than being dragged)?

Billy-no-Money

grizzly1911 wrote: »

Thanks good point.

I will have a look at that, if adjustment doesn't fix it.

I brought the special nut (£4 at Chainreaction) to remove the cassette. I needed to do this to replace the wheel guard between the spokes and cassette. I know it wasn't strictly necessary to replace this bit.

The wheel guard shattered when the chain went into it. Not sure whether the dropout broke first or whether it broke because of a chain or derailleur failure, both of which were destroyed. Is was only being used on road.

Sounds to me like your chain was very worn - I've had the same thing. What I think happens is that the chain links no longer run smoothly through the derailleur (rear mech), so it snags and gets pulled into the wheel. Before this happened did the chain run smoothly if you turned the pedals backwards?

If this is the case, then your cassette will definitely need replacing.

The 'dropout' you're referring to, by the way, is probably the 'hanger'; this is (I think) made of steel and designed to bend or break sacrificially, protecting the dropout itself, which is part of the frame. This (again I think) is necessary on aluminium frames, because you can't bend them back into shape.

thelawnet

IME I replace a cassette with every chain, but the derailleur rarely needs replacing. If you look at the different chain rings on it you can see the teeth. Probably you'll find some (the gears you use most often) are worn more than others - have a look at the extent to which the individual teeth are worn down.